2009-09-22 00:01:57 +00:00
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/*
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ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
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* Memory merging support.
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*
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* This code enables dynamic sharing of identical pages found in different
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* memory areas, even if they are not shared by fork()
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*
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2009-09-22 00:02:06 +00:00
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* Copyright (C) 2008-2009 Red Hat, Inc.
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ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
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* Authors:
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* Izik Eidus
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* Andrea Arcangeli
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* Chris Wright
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2009-09-22 00:02:06 +00:00
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* Hugh Dickins
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
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*
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* This work is licensed under the terms of the GNU GPL, version 2.
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2009-09-22 00:01:57 +00:00
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*/
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#include <linux/errno.h>
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ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
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#include <linux/mm.h>
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#include <linux/fs.h>
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2009-09-22 00:01:57 +00:00
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#include <linux/mman.h>
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
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#include <linux/sched.h>
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#include <linux/rwsem.h>
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#include <linux/pagemap.h>
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#include <linux/rmap.h>
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#include <linux/spinlock.h>
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#include <linux/jhash.h>
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#include <linux/delay.h>
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#include <linux/kthread.h>
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#include <linux/wait.h>
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#include <linux/slab.h>
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#include <linux/rbtree.h>
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ksm: memory hotremove migration only
The previous patch enables page migration of ksm pages, but that soon gets
into trouble: not surprising, since we're using the ksm page lock to lock
operations on its stable_node, but page migration switches the page whose
lock is to be used for that. Another layer of locking would fix it, but
do we need that yet?
Do we actually need page migration of ksm pages? Yes, memory hotremove
needs to offline sections of memory: and since we stopped allocating ksm
pages with GFP_HIGHUSER, they will tend to be GFP_HIGHUSER_MOVABLE
candidates for migration.
But KSM is currently unconscious of NUMA issues, happily merging pages
from different NUMA nodes: at present the rule must be, not to use
MADV_MERGEABLE where you care about NUMA. So no, NUMA page migration of
ksm pages does not make sense yet.
So, to complete support for ksm swapping we need to make hotremove safe.
ksm_memory_callback() take ksm_thread_mutex when MEM_GOING_OFFLINE and
release it when MEM_OFFLINE or MEM_CANCEL_OFFLINE. But if mapped pages
are freed before migration reaches them, stable_nodes may be left still
pointing to struct pages which have been removed from the system: the
stable_node needs to identify a page by pfn rather than page pointer, then
it can safely prune them when MEM_OFFLINE.
And make NUMA migration skip PageKsm pages where it skips PageReserved.
But it's only when we reach unmap_and_move() that the page lock is taken
and we can be sure that raised pagecount has prevented a PageAnon from
being upgraded: so add offlining arg to migrate_pages(), to migrate ksm
page when offlining (has sufficient locking) but reject it otherwise.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:33 +00:00
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#include <linux/memory.h>
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
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#include <linux/mmu_notifier.h>
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2009-09-23 22:56:04 +00:00
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#include <linux/swap.h>
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2009-09-22 00:01:57 +00:00
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#include <linux/ksm.h>
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2010-08-10 00:20:02 +00:00
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#include <linux/hash.h>
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2011-01-13 23:47:10 +00:00
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#include <linux/freezer.h>
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2011-05-25 00:11:40 +00:00
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#include <linux/oom.h>
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2009-09-22 00:01:57 +00:00
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
#include <asm/tlbflush.h>
|
2009-12-15 01:59:22 +00:00
|
|
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#include "internal.h"
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
|
|
|
/*
|
|
|
|
* A few notes about the KSM scanning process,
|
|
|
|
* to make it easier to understand the data structures below:
|
|
|
|
*
|
|
|
|
* In order to reduce excessive scanning, KSM sorts the memory pages by their
|
|
|
|
* contents into a data structure that holds pointers to the pages' locations.
|
|
|
|
*
|
|
|
|
* Since the contents of the pages may change at any moment, KSM cannot just
|
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|
|
* insert the pages into a normal sorted tree and expect it to find anything.
|
|
|
|
* Therefore KSM uses two data structures - the stable and the unstable tree.
|
|
|
|
*
|
|
|
|
* The stable tree holds pointers to all the merged pages (ksm pages), sorted
|
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|
|
* by their contents. Because each such page is write-protected, searching on
|
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|
|
* this tree is fully assured to be working (except when pages are unmapped),
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|
* and therefore this tree is called the stable tree.
|
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|
|
*
|
|
|
|
* In addition to the stable tree, KSM uses a second data structure called the
|
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|
|
* unstable tree: this tree holds pointers to pages which have been found to
|
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|
|
* be "unchanged for a period of time". The unstable tree sorts these pages
|
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|
|
* by their contents, but since they are not write-protected, KSM cannot rely
|
|
|
|
* upon the unstable tree to work correctly - the unstable tree is liable to
|
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|
|
* be corrupted as its contents are modified, and so it is called unstable.
|
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|
|
*
|
|
|
|
* KSM solves this problem by several techniques:
|
|
|
|
*
|
|
|
|
* 1) The unstable tree is flushed every time KSM completes scanning all
|
|
|
|
* memory areas, and then the tree is rebuilt again from the beginning.
|
|
|
|
* 2) KSM will only insert into the unstable tree, pages whose hash value
|
|
|
|
* has not changed since the previous scan of all memory areas.
|
|
|
|
* 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
|
|
|
|
* colors of the nodes and not on their contents, assuring that even when
|
|
|
|
* the tree gets "corrupted" it won't get out of balance, so scanning time
|
|
|
|
* remains the same (also, searching and inserting nodes in an rbtree uses
|
|
|
|
* the same algorithm, so we have no overhead when we flush and rebuild).
|
|
|
|
* 4) KSM never flushes the stable tree, which means that even if it were to
|
|
|
|
* take 10 attempts to find a page in the unstable tree, once it is found,
|
|
|
|
* it is secured in the stable tree. (When we scan a new page, we first
|
|
|
|
* compare it against the stable tree, and then against the unstable tree.)
|
|
|
|
*/
|
|
|
|
|
|
|
|
/**
|
|
|
|
* struct mm_slot - ksm information per mm that is being scanned
|
|
|
|
* @link: link to the mm_slots hash list
|
|
|
|
* @mm_list: link into the mm_slots list, rooted in ksm_mm_head
|
2009-12-15 01:59:19 +00:00
|
|
|
* @rmap_list: head for this mm_slot's singly-linked list of rmap_items
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
* @mm: the mm that this information is valid for
|
|
|
|
*/
|
|
|
|
struct mm_slot {
|
|
|
|
struct hlist_node link;
|
|
|
|
struct list_head mm_list;
|
2009-12-15 01:59:19 +00:00
|
|
|
struct rmap_item *rmap_list;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
struct mm_struct *mm;
|
|
|
|
};
|
|
|
|
|
|
|
|
/**
|
|
|
|
* struct ksm_scan - cursor for scanning
|
|
|
|
* @mm_slot: the current mm_slot we are scanning
|
|
|
|
* @address: the next address inside that to be scanned
|
2009-12-15 01:59:19 +00:00
|
|
|
* @rmap_list: link to the next rmap to be scanned in the rmap_list
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
* @seqnr: count of completed full scans (needed when removing unstable node)
|
|
|
|
*
|
|
|
|
* There is only the one ksm_scan instance of this cursor structure.
|
|
|
|
*/
|
|
|
|
struct ksm_scan {
|
|
|
|
struct mm_slot *mm_slot;
|
|
|
|
unsigned long address;
|
2009-12-15 01:59:19 +00:00
|
|
|
struct rmap_item **rmap_list;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
unsigned long seqnr;
|
|
|
|
};
|
|
|
|
|
2009-12-15 01:59:20 +00:00
|
|
|
/**
|
|
|
|
* struct stable_node - node of the stable rbtree
|
|
|
|
* @node: rb node of this ksm page in the stable tree
|
|
|
|
* @hlist: hlist head of rmap_items using this ksm page
|
ksm: memory hotremove migration only
The previous patch enables page migration of ksm pages, but that soon gets
into trouble: not surprising, since we're using the ksm page lock to lock
operations on its stable_node, but page migration switches the page whose
lock is to be used for that. Another layer of locking would fix it, but
do we need that yet?
Do we actually need page migration of ksm pages? Yes, memory hotremove
needs to offline sections of memory: and since we stopped allocating ksm
pages with GFP_HIGHUSER, they will tend to be GFP_HIGHUSER_MOVABLE
candidates for migration.
But KSM is currently unconscious of NUMA issues, happily merging pages
from different NUMA nodes: at present the rule must be, not to use
MADV_MERGEABLE where you care about NUMA. So no, NUMA page migration of
ksm pages does not make sense yet.
So, to complete support for ksm swapping we need to make hotremove safe.
ksm_memory_callback() take ksm_thread_mutex when MEM_GOING_OFFLINE and
release it when MEM_OFFLINE or MEM_CANCEL_OFFLINE. But if mapped pages
are freed before migration reaches them, stable_nodes may be left still
pointing to struct pages which have been removed from the system: the
stable_node needs to identify a page by pfn rather than page pointer, then
it can safely prune them when MEM_OFFLINE.
And make NUMA migration skip PageKsm pages where it skips PageReserved.
But it's only when we reach unmap_and_move() that the page lock is taken
and we can be sure that raised pagecount has prevented a PageAnon from
being upgraded: so add offlining arg to migrate_pages(), to migrate ksm
page when offlining (has sufficient locking) but reject it otherwise.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:33 +00:00
|
|
|
* @kpfn: page frame number of this ksm page
|
2009-12-15 01:59:20 +00:00
|
|
|
*/
|
|
|
|
struct stable_node {
|
|
|
|
struct rb_node node;
|
|
|
|
struct hlist_head hlist;
|
ksm: memory hotremove migration only
The previous patch enables page migration of ksm pages, but that soon gets
into trouble: not surprising, since we're using the ksm page lock to lock
operations on its stable_node, but page migration switches the page whose
lock is to be used for that. Another layer of locking would fix it, but
do we need that yet?
Do we actually need page migration of ksm pages? Yes, memory hotremove
needs to offline sections of memory: and since we stopped allocating ksm
pages with GFP_HIGHUSER, they will tend to be GFP_HIGHUSER_MOVABLE
candidates for migration.
But KSM is currently unconscious of NUMA issues, happily merging pages
from different NUMA nodes: at present the rule must be, not to use
MADV_MERGEABLE where you care about NUMA. So no, NUMA page migration of
ksm pages does not make sense yet.
So, to complete support for ksm swapping we need to make hotremove safe.
ksm_memory_callback() take ksm_thread_mutex when MEM_GOING_OFFLINE and
release it when MEM_OFFLINE or MEM_CANCEL_OFFLINE. But if mapped pages
are freed before migration reaches them, stable_nodes may be left still
pointing to struct pages which have been removed from the system: the
stable_node needs to identify a page by pfn rather than page pointer, then
it can safely prune them when MEM_OFFLINE.
And make NUMA migration skip PageKsm pages where it skips PageReserved.
But it's only when we reach unmap_and_move() that the page lock is taken
and we can be sure that raised pagecount has prevented a PageAnon from
being upgraded: so add offlining arg to migrate_pages(), to migrate ksm
page when offlining (has sufficient locking) but reject it otherwise.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:33 +00:00
|
|
|
unsigned long kpfn;
|
2009-12-15 01:59:20 +00:00
|
|
|
};
|
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
/**
|
|
|
|
* struct rmap_item - reverse mapping item for virtual addresses
|
2009-12-15 01:59:19 +00:00
|
|
|
* @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
|
2009-12-15 01:59:25 +00:00
|
|
|
* @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
* @mm: the memory structure this rmap_item is pointing into
|
|
|
|
* @address: the virtual address this rmap_item tracks (+ flags in low bits)
|
|
|
|
* @oldchecksum: previous checksum of the page at that virtual address
|
2009-12-15 01:59:20 +00:00
|
|
|
* @node: rb node of this rmap_item in the unstable tree
|
|
|
|
* @head: pointer to stable_node heading this list in the stable tree
|
|
|
|
* @hlist: link into hlist of rmap_items hanging off that stable_node
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
*/
|
|
|
|
struct rmap_item {
|
2009-12-15 01:59:19 +00:00
|
|
|
struct rmap_item *rmap_list;
|
2009-12-15 01:59:25 +00:00
|
|
|
struct anon_vma *anon_vma; /* when stable */
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
struct mm_struct *mm;
|
|
|
|
unsigned long address; /* + low bits used for flags below */
|
2009-12-15 01:59:20 +00:00
|
|
|
unsigned int oldchecksum; /* when unstable */
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
union {
|
2009-12-15 01:59:20 +00:00
|
|
|
struct rb_node node; /* when node of unstable tree */
|
|
|
|
struct { /* when listed from stable tree */
|
|
|
|
struct stable_node *head;
|
|
|
|
struct hlist_node hlist;
|
|
|
|
};
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
};
|
|
|
|
};
|
|
|
|
|
|
|
|
#define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
|
2009-12-15 01:59:20 +00:00
|
|
|
#define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
|
|
|
|
#define STABLE_FLAG 0x200 /* is listed from the stable tree */
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
|
|
|
/* The stable and unstable tree heads */
|
|
|
|
static struct rb_root root_stable_tree = RB_ROOT;
|
|
|
|
static struct rb_root root_unstable_tree = RB_ROOT;
|
|
|
|
|
2010-08-10 00:20:02 +00:00
|
|
|
#define MM_SLOTS_HASH_SHIFT 10
|
|
|
|
#define MM_SLOTS_HASH_HEADS (1 << MM_SLOTS_HASH_SHIFT)
|
|
|
|
static struct hlist_head mm_slots_hash[MM_SLOTS_HASH_HEADS];
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
|
|
|
static struct mm_slot ksm_mm_head = {
|
|
|
|
.mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
|
|
|
|
};
|
|
|
|
static struct ksm_scan ksm_scan = {
|
|
|
|
.mm_slot = &ksm_mm_head,
|
|
|
|
};
|
|
|
|
|
|
|
|
static struct kmem_cache *rmap_item_cache;
|
2009-12-15 01:59:20 +00:00
|
|
|
static struct kmem_cache *stable_node_cache;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
static struct kmem_cache *mm_slot_cache;
|
|
|
|
|
|
|
|
/* The number of nodes in the stable tree */
|
2009-09-22 00:02:09 +00:00
|
|
|
static unsigned long ksm_pages_shared;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
2009-09-22 00:02:10 +00:00
|
|
|
/* The number of page slots additionally sharing those nodes */
|
2009-09-22 00:02:09 +00:00
|
|
|
static unsigned long ksm_pages_sharing;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
2009-09-22 00:02:11 +00:00
|
|
|
/* The number of nodes in the unstable tree */
|
|
|
|
static unsigned long ksm_pages_unshared;
|
|
|
|
|
|
|
|
/* The number of rmap_items in use: to calculate pages_volatile */
|
|
|
|
static unsigned long ksm_rmap_items;
|
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
/* Number of pages ksmd should scan in one batch */
|
2009-09-23 22:56:04 +00:00
|
|
|
static unsigned int ksm_thread_pages_to_scan = 100;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
|
|
|
/* Milliseconds ksmd should sleep between batches */
|
2009-09-22 00:02:23 +00:00
|
|
|
static unsigned int ksm_thread_sleep_millisecs = 20;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
|
|
|
#define KSM_RUN_STOP 0
|
|
|
|
#define KSM_RUN_MERGE 1
|
|
|
|
#define KSM_RUN_UNMERGE 2
|
2009-09-23 22:56:04 +00:00
|
|
|
static unsigned int ksm_run = KSM_RUN_STOP;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
|
|
|
static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
|
|
|
|
static DEFINE_MUTEX(ksm_thread_mutex);
|
|
|
|
static DEFINE_SPINLOCK(ksm_mmlist_lock);
|
|
|
|
|
|
|
|
#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
|
|
|
|
sizeof(struct __struct), __alignof__(struct __struct),\
|
|
|
|
(__flags), NULL)
|
|
|
|
|
|
|
|
static int __init ksm_slab_init(void)
|
|
|
|
{
|
|
|
|
rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
|
|
|
|
if (!rmap_item_cache)
|
|
|
|
goto out;
|
|
|
|
|
2009-12-15 01:59:20 +00:00
|
|
|
stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
|
|
|
|
if (!stable_node_cache)
|
|
|
|
goto out_free1;
|
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
|
|
|
|
if (!mm_slot_cache)
|
2009-12-15 01:59:20 +00:00
|
|
|
goto out_free2;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
|
|
|
return 0;
|
|
|
|
|
2009-12-15 01:59:20 +00:00
|
|
|
out_free2:
|
|
|
|
kmem_cache_destroy(stable_node_cache);
|
|
|
|
out_free1:
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
kmem_cache_destroy(rmap_item_cache);
|
|
|
|
out:
|
|
|
|
return -ENOMEM;
|
|
|
|
}
|
|
|
|
|
|
|
|
static void __init ksm_slab_free(void)
|
|
|
|
{
|
|
|
|
kmem_cache_destroy(mm_slot_cache);
|
2009-12-15 01:59:20 +00:00
|
|
|
kmem_cache_destroy(stable_node_cache);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
kmem_cache_destroy(rmap_item_cache);
|
|
|
|
mm_slot_cache = NULL;
|
|
|
|
}
|
|
|
|
|
|
|
|
static inline struct rmap_item *alloc_rmap_item(void)
|
|
|
|
{
|
2009-09-22 00:02:11 +00:00
|
|
|
struct rmap_item *rmap_item;
|
|
|
|
|
|
|
|
rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
|
|
|
|
if (rmap_item)
|
|
|
|
ksm_rmap_items++;
|
|
|
|
return rmap_item;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
static inline void free_rmap_item(struct rmap_item *rmap_item)
|
|
|
|
{
|
2009-09-22 00:02:11 +00:00
|
|
|
ksm_rmap_items--;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
rmap_item->mm = NULL; /* debug safety */
|
|
|
|
kmem_cache_free(rmap_item_cache, rmap_item);
|
|
|
|
}
|
|
|
|
|
2009-12-15 01:59:20 +00:00
|
|
|
static inline struct stable_node *alloc_stable_node(void)
|
|
|
|
{
|
|
|
|
return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
|
|
|
|
}
|
|
|
|
|
|
|
|
static inline void free_stable_node(struct stable_node *stable_node)
|
|
|
|
{
|
|
|
|
kmem_cache_free(stable_node_cache, stable_node);
|
|
|
|
}
|
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
static inline struct mm_slot *alloc_mm_slot(void)
|
|
|
|
{
|
|
|
|
if (!mm_slot_cache) /* initialization failed */
|
|
|
|
return NULL;
|
|
|
|
return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
|
|
|
|
}
|
|
|
|
|
|
|
|
static inline void free_mm_slot(struct mm_slot *mm_slot)
|
|
|
|
{
|
|
|
|
kmem_cache_free(mm_slot_cache, mm_slot);
|
|
|
|
}
|
|
|
|
|
|
|
|
static struct mm_slot *get_mm_slot(struct mm_struct *mm)
|
|
|
|
{
|
|
|
|
struct mm_slot *mm_slot;
|
|
|
|
struct hlist_head *bucket;
|
|
|
|
struct hlist_node *node;
|
|
|
|
|
2010-08-10 00:20:02 +00:00
|
|
|
bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
hlist_for_each_entry(mm_slot, node, bucket, link) {
|
|
|
|
if (mm == mm_slot->mm)
|
|
|
|
return mm_slot;
|
|
|
|
}
|
|
|
|
return NULL;
|
|
|
|
}
|
|
|
|
|
|
|
|
static void insert_to_mm_slots_hash(struct mm_struct *mm,
|
|
|
|
struct mm_slot *mm_slot)
|
|
|
|
{
|
|
|
|
struct hlist_head *bucket;
|
|
|
|
|
2010-08-10 00:20:02 +00:00
|
|
|
bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
mm_slot->mm = mm;
|
|
|
|
hlist_add_head(&mm_slot->link, bucket);
|
|
|
|
}
|
|
|
|
|
|
|
|
static inline int in_stable_tree(struct rmap_item *rmap_item)
|
|
|
|
{
|
|
|
|
return rmap_item->address & STABLE_FLAG;
|
|
|
|
}
|
|
|
|
|
2009-09-22 00:02:26 +00:00
|
|
|
/*
|
|
|
|
* ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
|
|
|
|
* page tables after it has passed through ksm_exit() - which, if necessary,
|
|
|
|
* takes mmap_sem briefly to serialize against them. ksm_exit() does not set
|
|
|
|
* a special flag: they can just back out as soon as mm_users goes to zero.
|
|
|
|
* ksm_test_exit() is used throughout to make this test for exit: in some
|
|
|
|
* places for correctness, in some places just to avoid unnecessary work.
|
|
|
|
*/
|
|
|
|
static inline bool ksm_test_exit(struct mm_struct *mm)
|
|
|
|
{
|
|
|
|
return atomic_read(&mm->mm_users) == 0;
|
|
|
|
}
|
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
/*
|
|
|
|
* We use break_ksm to break COW on a ksm page: it's a stripped down
|
|
|
|
*
|
|
|
|
* if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
|
|
|
|
* put_page(page);
|
|
|
|
*
|
|
|
|
* but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
|
|
|
|
* in case the application has unmapped and remapped mm,addr meanwhile.
|
|
|
|
* Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
|
|
|
|
* mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
|
|
|
|
*/
|
2009-09-22 00:02:16 +00:00
|
|
|
static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
{
|
|
|
|
struct page *page;
|
2009-09-22 00:02:16 +00:00
|
|
|
int ret = 0;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
|
|
|
do {
|
|
|
|
cond_resched();
|
|
|
|
page = follow_page(vma, addr, FOLL_GET);
|
2010-04-23 17:18:10 +00:00
|
|
|
if (IS_ERR_OR_NULL(page))
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
break;
|
|
|
|
if (PageKsm(page))
|
|
|
|
ret = handle_mm_fault(vma->vm_mm, vma, addr,
|
|
|
|
FAULT_FLAG_WRITE);
|
|
|
|
else
|
|
|
|
ret = VM_FAULT_WRITE;
|
|
|
|
put_page(page);
|
2009-09-22 00:02:16 +00:00
|
|
|
} while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
|
|
|
|
/*
|
|
|
|
* We must loop because handle_mm_fault() may back out if there's
|
|
|
|
* any difficulty e.g. if pte accessed bit gets updated concurrently.
|
|
|
|
*
|
|
|
|
* VM_FAULT_WRITE is what we have been hoping for: it indicates that
|
|
|
|
* COW has been broken, even if the vma does not permit VM_WRITE;
|
|
|
|
* but note that a concurrent fault might break PageKsm for us.
|
|
|
|
*
|
|
|
|
* VM_FAULT_SIGBUS could occur if we race with truncation of the
|
|
|
|
* backing file, which also invalidates anonymous pages: that's
|
|
|
|
* okay, that truncation will have unmapped the PageKsm for us.
|
|
|
|
*
|
|
|
|
* VM_FAULT_OOM: at the time of writing (late July 2009), setting
|
|
|
|
* aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
|
|
|
|
* current task has TIF_MEMDIE set, and will be OOM killed on return
|
|
|
|
* to user; and ksmd, having no mm, would never be chosen for that.
|
|
|
|
*
|
|
|
|
* But if the mm is in a limited mem_cgroup, then the fault may fail
|
|
|
|
* with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
|
|
|
|
* even ksmd can fail in this way - though it's usually breaking ksm
|
|
|
|
* just to undo a merge it made a moment before, so unlikely to oom.
|
|
|
|
*
|
|
|
|
* That's a pity: we might therefore have more kernel pages allocated
|
|
|
|
* than we're counting as nodes in the stable tree; but ksm_do_scan
|
|
|
|
* will retry to break_cow on each pass, so should recover the page
|
|
|
|
* in due course. The important thing is to not let VM_MERGEABLE
|
|
|
|
* be cleared while any such pages might remain in the area.
|
|
|
|
*/
|
|
|
|
return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
|
|
|
|
2012-03-21 23:34:11 +00:00
|
|
|
static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
|
|
|
|
unsigned long addr)
|
|
|
|
{
|
|
|
|
struct vm_area_struct *vma;
|
|
|
|
if (ksm_test_exit(mm))
|
|
|
|
return NULL;
|
|
|
|
vma = find_vma(mm, addr);
|
|
|
|
if (!vma || vma->vm_start > addr)
|
|
|
|
return NULL;
|
|
|
|
if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
|
|
|
|
return NULL;
|
|
|
|
return vma;
|
|
|
|
}
|
|
|
|
|
2009-12-15 01:59:18 +00:00
|
|
|
static void break_cow(struct rmap_item *rmap_item)
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
{
|
2009-12-15 01:59:18 +00:00
|
|
|
struct mm_struct *mm = rmap_item->mm;
|
|
|
|
unsigned long addr = rmap_item->address;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
struct vm_area_struct *vma;
|
|
|
|
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
/*
|
|
|
|
* It is not an accident that whenever we want to break COW
|
|
|
|
* to undo, we also need to drop a reference to the anon_vma.
|
|
|
|
*/
|
2011-03-22 23:32:46 +00:00
|
|
|
put_anon_vma(rmap_item->anon_vma);
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
|
2009-09-22 00:02:15 +00:00
|
|
|
down_read(&mm->mmap_sem);
|
2012-03-21 23:34:11 +00:00
|
|
|
vma = find_mergeable_vma(mm, addr);
|
|
|
|
if (vma)
|
|
|
|
break_ksm(vma, addr);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
up_read(&mm->mmap_sem);
|
|
|
|
}
|
|
|
|
|
2011-01-13 23:47:19 +00:00
|
|
|
static struct page *page_trans_compound_anon(struct page *page)
|
|
|
|
{
|
|
|
|
if (PageTransCompound(page)) {
|
2011-01-13 23:47:20 +00:00
|
|
|
struct page *head = compound_trans_head(page);
|
2011-01-13 23:47:19 +00:00
|
|
|
/*
|
2011-01-13 23:47:20 +00:00
|
|
|
* head may actually be splitted and freed from under
|
|
|
|
* us but it's ok here.
|
2011-01-13 23:47:19 +00:00
|
|
|
*/
|
|
|
|
if (PageAnon(head))
|
|
|
|
return head;
|
|
|
|
}
|
|
|
|
return NULL;
|
|
|
|
}
|
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
static struct page *get_mergeable_page(struct rmap_item *rmap_item)
|
|
|
|
{
|
|
|
|
struct mm_struct *mm = rmap_item->mm;
|
|
|
|
unsigned long addr = rmap_item->address;
|
|
|
|
struct vm_area_struct *vma;
|
|
|
|
struct page *page;
|
|
|
|
|
|
|
|
down_read(&mm->mmap_sem);
|
2012-03-21 23:34:11 +00:00
|
|
|
vma = find_mergeable_vma(mm, addr);
|
|
|
|
if (!vma)
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
goto out;
|
|
|
|
|
|
|
|
page = follow_page(vma, addr, FOLL_GET);
|
2010-04-23 17:18:10 +00:00
|
|
|
if (IS_ERR_OR_NULL(page))
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
goto out;
|
2011-01-13 23:47:19 +00:00
|
|
|
if (PageAnon(page) || page_trans_compound_anon(page)) {
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
flush_anon_page(vma, page, addr);
|
|
|
|
flush_dcache_page(page);
|
|
|
|
} else {
|
|
|
|
put_page(page);
|
|
|
|
out: page = NULL;
|
|
|
|
}
|
|
|
|
up_read(&mm->mmap_sem);
|
|
|
|
return page;
|
|
|
|
}
|
|
|
|
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
static void remove_node_from_stable_tree(struct stable_node *stable_node)
|
|
|
|
{
|
|
|
|
struct rmap_item *rmap_item;
|
|
|
|
struct hlist_node *hlist;
|
|
|
|
|
|
|
|
hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
|
|
|
|
if (rmap_item->hlist.next)
|
|
|
|
ksm_pages_sharing--;
|
|
|
|
else
|
|
|
|
ksm_pages_shared--;
|
2011-03-22 23:32:46 +00:00
|
|
|
put_anon_vma(rmap_item->anon_vma);
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
rmap_item->address &= PAGE_MASK;
|
|
|
|
cond_resched();
|
|
|
|
}
|
|
|
|
|
|
|
|
rb_erase(&stable_node->node, &root_stable_tree);
|
|
|
|
free_stable_node(stable_node);
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* get_ksm_page: checks if the page indicated by the stable node
|
|
|
|
* is still its ksm page, despite having held no reference to it.
|
|
|
|
* In which case we can trust the content of the page, and it
|
|
|
|
* returns the gotten page; but if the page has now been zapped,
|
|
|
|
* remove the stale node from the stable tree and return NULL.
|
|
|
|
*
|
|
|
|
* You would expect the stable_node to hold a reference to the ksm page.
|
|
|
|
* But if it increments the page's count, swapping out has to wait for
|
|
|
|
* ksmd to come around again before it can free the page, which may take
|
|
|
|
* seconds or even minutes: much too unresponsive. So instead we use a
|
|
|
|
* "keyhole reference": access to the ksm page from the stable node peeps
|
|
|
|
* out through its keyhole to see if that page still holds the right key,
|
|
|
|
* pointing back to this stable node. This relies on freeing a PageAnon
|
|
|
|
* page to reset its page->mapping to NULL, and relies on no other use of
|
|
|
|
* a page to put something that might look like our key in page->mapping.
|
|
|
|
*
|
|
|
|
* include/linux/pagemap.h page_cache_get_speculative() is a good reference,
|
|
|
|
* but this is different - made simpler by ksm_thread_mutex being held, but
|
|
|
|
* interesting for assuming that no other use of the struct page could ever
|
|
|
|
* put our expected_mapping into page->mapping (or a field of the union which
|
|
|
|
* coincides with page->mapping). The RCU calls are not for KSM at all, but
|
|
|
|
* to keep the page_count protocol described with page_cache_get_speculative.
|
|
|
|
*
|
|
|
|
* Note: it is possible that get_ksm_page() will return NULL one moment,
|
|
|
|
* then page the next, if the page is in between page_freeze_refs() and
|
|
|
|
* page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
|
|
|
|
* is on its way to being freed; but it is an anomaly to bear in mind.
|
|
|
|
*/
|
|
|
|
static struct page *get_ksm_page(struct stable_node *stable_node)
|
|
|
|
{
|
|
|
|
struct page *page;
|
|
|
|
void *expected_mapping;
|
|
|
|
|
ksm: memory hotremove migration only
The previous patch enables page migration of ksm pages, but that soon gets
into trouble: not surprising, since we're using the ksm page lock to lock
operations on its stable_node, but page migration switches the page whose
lock is to be used for that. Another layer of locking would fix it, but
do we need that yet?
Do we actually need page migration of ksm pages? Yes, memory hotremove
needs to offline sections of memory: and since we stopped allocating ksm
pages with GFP_HIGHUSER, they will tend to be GFP_HIGHUSER_MOVABLE
candidates for migration.
But KSM is currently unconscious of NUMA issues, happily merging pages
from different NUMA nodes: at present the rule must be, not to use
MADV_MERGEABLE where you care about NUMA. So no, NUMA page migration of
ksm pages does not make sense yet.
So, to complete support for ksm swapping we need to make hotremove safe.
ksm_memory_callback() take ksm_thread_mutex when MEM_GOING_OFFLINE and
release it when MEM_OFFLINE or MEM_CANCEL_OFFLINE. But if mapped pages
are freed before migration reaches them, stable_nodes may be left still
pointing to struct pages which have been removed from the system: the
stable_node needs to identify a page by pfn rather than page pointer, then
it can safely prune them when MEM_OFFLINE.
And make NUMA migration skip PageKsm pages where it skips PageReserved.
But it's only when we reach unmap_and_move() that the page lock is taken
and we can be sure that raised pagecount has prevented a PageAnon from
being upgraded: so add offlining arg to migrate_pages(), to migrate ksm
page when offlining (has sufficient locking) but reject it otherwise.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:33 +00:00
|
|
|
page = pfn_to_page(stable_node->kpfn);
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
expected_mapping = (void *)stable_node +
|
|
|
|
(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
|
|
|
|
rcu_read_lock();
|
|
|
|
if (page->mapping != expected_mapping)
|
|
|
|
goto stale;
|
|
|
|
if (!get_page_unless_zero(page))
|
|
|
|
goto stale;
|
|
|
|
if (page->mapping != expected_mapping) {
|
|
|
|
put_page(page);
|
|
|
|
goto stale;
|
|
|
|
}
|
|
|
|
rcu_read_unlock();
|
|
|
|
return page;
|
|
|
|
stale:
|
|
|
|
rcu_read_unlock();
|
|
|
|
remove_node_from_stable_tree(stable_node);
|
|
|
|
return NULL;
|
|
|
|
}
|
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
/*
|
|
|
|
* Removing rmap_item from stable or unstable tree.
|
|
|
|
* This function will clean the information from the stable/unstable tree.
|
|
|
|
*/
|
|
|
|
static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
|
|
|
|
{
|
2009-12-15 01:59:20 +00:00
|
|
|
if (rmap_item->address & STABLE_FLAG) {
|
|
|
|
struct stable_node *stable_node;
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
struct page *page;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
2009-12-15 01:59:20 +00:00
|
|
|
stable_node = rmap_item->head;
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
page = get_ksm_page(stable_node);
|
|
|
|
if (!page)
|
|
|
|
goto out;
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
lock_page(page);
|
2009-12-15 01:59:20 +00:00
|
|
|
hlist_del(&rmap_item->hlist);
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
unlock_page(page);
|
|
|
|
put_page(page);
|
2009-12-15 01:59:21 +00:00
|
|
|
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
if (stable_node->hlist.first)
|
|
|
|
ksm_pages_sharing--;
|
|
|
|
else
|
2009-12-15 01:59:20 +00:00
|
|
|
ksm_pages_shared--;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
2011-03-22 23:32:46 +00:00
|
|
|
put_anon_vma(rmap_item->anon_vma);
|
2009-12-15 01:59:16 +00:00
|
|
|
rmap_item->address &= PAGE_MASK;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
2009-12-15 01:59:20 +00:00
|
|
|
} else if (rmap_item->address & UNSTABLE_FLAG) {
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
unsigned char age;
|
|
|
|
/*
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
* Usually ksmd can and must skip the rb_erase, because
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
* root_unstable_tree was already reset to RB_ROOT.
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
* But be careful when an mm is exiting: do the rb_erase
|
|
|
|
* if this rmap_item was inserted by this scan, rather
|
|
|
|
* than left over from before.
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
*/
|
|
|
|
age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
|
2009-09-22 00:02:17 +00:00
|
|
|
BUG_ON(age > 1);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
if (!age)
|
|
|
|
rb_erase(&rmap_item->node, &root_unstable_tree);
|
2009-12-15 01:59:16 +00:00
|
|
|
|
2009-09-22 00:02:11 +00:00
|
|
|
ksm_pages_unshared--;
|
2009-12-15 01:59:16 +00:00
|
|
|
rmap_item->address &= PAGE_MASK;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
out:
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
cond_resched(); /* we're called from many long loops */
|
|
|
|
}
|
|
|
|
|
|
|
|
static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
|
2009-12-15 01:59:19 +00:00
|
|
|
struct rmap_item **rmap_list)
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
{
|
2009-12-15 01:59:19 +00:00
|
|
|
while (*rmap_list) {
|
|
|
|
struct rmap_item *rmap_item = *rmap_list;
|
|
|
|
*rmap_list = rmap_item->rmap_list;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
remove_rmap_item_from_tree(rmap_item);
|
|
|
|
free_rmap_item(rmap_item);
|
|
|
|
}
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
|
|
|
|
* than check every pte of a given vma, the locking doesn't quite work for
|
|
|
|
* that - an rmap_item is assigned to the stable tree after inserting ksm
|
|
|
|
* page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
|
|
|
|
* rmap_items from parent to child at fork time (so as not to waste time
|
|
|
|
* if exit comes before the next scan reaches it).
|
2009-09-22 00:02:15 +00:00
|
|
|
*
|
|
|
|
* Similarly, although we'd like to remove rmap_items (so updating counts
|
|
|
|
* and freeing memory) when unmerging an area, it's easier to leave that
|
|
|
|
* to the next pass of ksmd - consider, for example, how ksmd might be
|
|
|
|
* in cmp_and_merge_page on one of the rmap_items we would be removing.
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
*/
|
2009-09-22 00:02:16 +00:00
|
|
|
static int unmerge_ksm_pages(struct vm_area_struct *vma,
|
|
|
|
unsigned long start, unsigned long end)
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
{
|
|
|
|
unsigned long addr;
|
2009-09-22 00:02:16 +00:00
|
|
|
int err = 0;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
2009-09-22 00:02:16 +00:00
|
|
|
for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
if (ksm_test_exit(vma->vm_mm))
|
|
|
|
break;
|
2009-09-22 00:02:16 +00:00
|
|
|
if (signal_pending(current))
|
|
|
|
err = -ERESTARTSYS;
|
|
|
|
else
|
|
|
|
err = break_ksm(vma, addr);
|
|
|
|
}
|
|
|
|
return err;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
|
|
|
|
2009-09-22 00:02:23 +00:00
|
|
|
#ifdef CONFIG_SYSFS
|
|
|
|
/*
|
|
|
|
* Only called through the sysfs control interface:
|
|
|
|
*/
|
2009-09-22 00:02:16 +00:00
|
|
|
static int unmerge_and_remove_all_rmap_items(void)
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
{
|
|
|
|
struct mm_slot *mm_slot;
|
|
|
|
struct mm_struct *mm;
|
|
|
|
struct vm_area_struct *vma;
|
2009-09-22 00:02:16 +00:00
|
|
|
int err = 0;
|
|
|
|
|
|
|
|
spin_lock(&ksm_mmlist_lock);
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
|
2009-09-22 00:02:16 +00:00
|
|
|
struct mm_slot, mm_list);
|
|
|
|
spin_unlock(&ksm_mmlist_lock);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
for (mm_slot = ksm_scan.mm_slot;
|
|
|
|
mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
mm = mm_slot->mm;
|
|
|
|
down_read(&mm->mmap_sem);
|
|
|
|
for (vma = mm->mmap; vma; vma = vma->vm_next) {
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
if (ksm_test_exit(mm))
|
|
|
|
break;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
|
|
|
|
continue;
|
2009-09-22 00:02:16 +00:00
|
|
|
err = unmerge_ksm_pages(vma,
|
|
|
|
vma->vm_start, vma->vm_end);
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
if (err)
|
|
|
|
goto error;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
|
2009-12-15 01:59:19 +00:00
|
|
|
remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
|
2009-09-22 00:02:16 +00:00
|
|
|
|
|
|
|
spin_lock(&ksm_mmlist_lock);
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
|
2009-09-22 00:02:16 +00:00
|
|
|
struct mm_slot, mm_list);
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
if (ksm_test_exit(mm)) {
|
|
|
|
hlist_del(&mm_slot->link);
|
|
|
|
list_del(&mm_slot->mm_list);
|
|
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
|
|
|
|
|
|
free_mm_slot(mm_slot);
|
|
|
|
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
|
|
|
|
up_read(&mm->mmap_sem);
|
|
|
|
mmdrop(mm);
|
|
|
|
} else {
|
|
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
|
|
up_read(&mm->mmap_sem);
|
|
|
|
}
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
|
|
|
|
2009-09-22 00:02:16 +00:00
|
|
|
ksm_scan.seqnr = 0;
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
return 0;
|
|
|
|
|
|
|
|
error:
|
|
|
|
up_read(&mm->mmap_sem);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
spin_lock(&ksm_mmlist_lock);
|
2009-09-22 00:02:16 +00:00
|
|
|
ksm_scan.mm_slot = &ksm_mm_head;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
spin_unlock(&ksm_mmlist_lock);
|
2009-09-22 00:02:16 +00:00
|
|
|
return err;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
2009-09-22 00:02:23 +00:00
|
|
|
#endif /* CONFIG_SYSFS */
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
|
|
|
static u32 calc_checksum(struct page *page)
|
|
|
|
{
|
|
|
|
u32 checksum;
|
2011-11-25 15:14:39 +00:00
|
|
|
void *addr = kmap_atomic(page);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
checksum = jhash2(addr, PAGE_SIZE / 4, 17);
|
2011-11-25 15:14:39 +00:00
|
|
|
kunmap_atomic(addr);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
return checksum;
|
|
|
|
}
|
|
|
|
|
|
|
|
static int memcmp_pages(struct page *page1, struct page *page2)
|
|
|
|
{
|
|
|
|
char *addr1, *addr2;
|
|
|
|
int ret;
|
|
|
|
|
2011-11-25 15:14:39 +00:00
|
|
|
addr1 = kmap_atomic(page1);
|
|
|
|
addr2 = kmap_atomic(page2);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
ret = memcmp(addr1, addr2, PAGE_SIZE);
|
2011-11-25 15:14:39 +00:00
|
|
|
kunmap_atomic(addr2);
|
|
|
|
kunmap_atomic(addr1);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
return ret;
|
|
|
|
}
|
|
|
|
|
|
|
|
static inline int pages_identical(struct page *page1, struct page *page2)
|
|
|
|
{
|
|
|
|
return !memcmp_pages(page1, page2);
|
|
|
|
}
|
|
|
|
|
|
|
|
static int write_protect_page(struct vm_area_struct *vma, struct page *page,
|
|
|
|
pte_t *orig_pte)
|
|
|
|
{
|
|
|
|
struct mm_struct *mm = vma->vm_mm;
|
|
|
|
unsigned long addr;
|
|
|
|
pte_t *ptep;
|
|
|
|
spinlock_t *ptl;
|
|
|
|
int swapped;
|
|
|
|
int err = -EFAULT;
|
2012-10-08 23:33:35 +00:00
|
|
|
unsigned long mmun_start; /* For mmu_notifiers */
|
|
|
|
unsigned long mmun_end; /* For mmu_notifiers */
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
|
|
|
addr = page_address_in_vma(page, vma);
|
|
|
|
if (addr == -EFAULT)
|
|
|
|
goto out;
|
|
|
|
|
2011-01-13 23:47:19 +00:00
|
|
|
BUG_ON(PageTransCompound(page));
|
2012-10-08 23:33:35 +00:00
|
|
|
|
|
|
|
mmun_start = addr;
|
|
|
|
mmun_end = addr + PAGE_SIZE;
|
|
|
|
mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
|
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
ptep = page_check_address(page, mm, addr, &ptl, 0);
|
|
|
|
if (!ptep)
|
2012-10-08 23:33:35 +00:00
|
|
|
goto out_mn;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
ksm: fix bad user data when swapping
Building under memory pressure, with KSM on 2.6.36-rc5, collapsed with
an internal compiler error: typically indicating an error in swapping.
Perhaps there's a timing issue which makes it now more likely, perhaps
it's just a long time since I tried for so long: this bug goes back to
KSM swapping in 2.6.33.
Notice how reuse_swap_page() allows an exclusive page to be reused, but
only does SetPageDirty if it can delete it from swap cache right then -
if it's currently under Writeback, it has to be left in cache and we
don't SetPageDirty, but the page can be reused. Fine, the dirty bit
will get set in the pte; but notice how zap_pte_range() does not bother
to transfer pte_dirty to page_dirty when unmapping a PageAnon.
If KSM chooses to share such a page, it will look like a clean copy of
swapcache, and not be written out to swap when its memory is needed;
then stale data read back from swap when it's needed again.
We could fix this in reuse_swap_page() (or even refuse to reuse a
page under writeback), but it's more honest to fix my oversight in
KSM's write_protect_page(). Several days of testing on three machines
confirms that this fixes the issue they showed.
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-10-03 00:49:08 +00:00
|
|
|
if (pte_write(*ptep) || pte_dirty(*ptep)) {
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
pte_t entry;
|
|
|
|
|
|
|
|
swapped = PageSwapCache(page);
|
|
|
|
flush_cache_page(vma, addr, page_to_pfn(page));
|
|
|
|
/*
|
2011-03-31 01:57:33 +00:00
|
|
|
* Ok this is tricky, when get_user_pages_fast() run it doesn't
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
* take any lock, therefore the check that we are going to make
|
|
|
|
* with the pagecount against the mapcount is racey and
|
|
|
|
* O_DIRECT can happen right after the check.
|
|
|
|
* So we clear the pte and flush the tlb before the check
|
|
|
|
* this assure us that no O_DIRECT can happen after the check
|
|
|
|
* or in the middle of the check.
|
|
|
|
*/
|
|
|
|
entry = ptep_clear_flush(vma, addr, ptep);
|
|
|
|
/*
|
|
|
|
* Check that no O_DIRECT or similar I/O is in progress on the
|
|
|
|
* page
|
|
|
|
*/
|
2009-12-15 01:59:17 +00:00
|
|
|
if (page_mapcount(page) + 1 + swapped != page_count(page)) {
|
2010-03-23 20:35:26 +00:00
|
|
|
set_pte_at(mm, addr, ptep, entry);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
goto out_unlock;
|
|
|
|
}
|
ksm: fix bad user data when swapping
Building under memory pressure, with KSM on 2.6.36-rc5, collapsed with
an internal compiler error: typically indicating an error in swapping.
Perhaps there's a timing issue which makes it now more likely, perhaps
it's just a long time since I tried for so long: this bug goes back to
KSM swapping in 2.6.33.
Notice how reuse_swap_page() allows an exclusive page to be reused, but
only does SetPageDirty if it can delete it from swap cache right then -
if it's currently under Writeback, it has to be left in cache and we
don't SetPageDirty, but the page can be reused. Fine, the dirty bit
will get set in the pte; but notice how zap_pte_range() does not bother
to transfer pte_dirty to page_dirty when unmapping a PageAnon.
If KSM chooses to share such a page, it will look like a clean copy of
swapcache, and not be written out to swap when its memory is needed;
then stale data read back from swap when it's needed again.
We could fix this in reuse_swap_page() (or even refuse to reuse a
page under writeback), but it's more honest to fix my oversight in
KSM's write_protect_page(). Several days of testing on three machines
confirms that this fixes the issue they showed.
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-10-03 00:49:08 +00:00
|
|
|
if (pte_dirty(entry))
|
|
|
|
set_page_dirty(page);
|
|
|
|
entry = pte_mkclean(pte_wrprotect(entry));
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
set_pte_at_notify(mm, addr, ptep, entry);
|
|
|
|
}
|
|
|
|
*orig_pte = *ptep;
|
|
|
|
err = 0;
|
|
|
|
|
|
|
|
out_unlock:
|
|
|
|
pte_unmap_unlock(ptep, ptl);
|
2012-10-08 23:33:35 +00:00
|
|
|
out_mn:
|
|
|
|
mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
out:
|
|
|
|
return err;
|
|
|
|
}
|
|
|
|
|
|
|
|
/**
|
|
|
|
* replace_page - replace page in vma by new ksm page
|
2009-12-15 01:59:18 +00:00
|
|
|
* @vma: vma that holds the pte pointing to page
|
|
|
|
* @page: the page we are replacing by kpage
|
|
|
|
* @kpage: the ksm page we replace page by
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
* @orig_pte: the original value of the pte
|
|
|
|
*
|
|
|
|
* Returns 0 on success, -EFAULT on failure.
|
|
|
|
*/
|
2009-12-15 01:59:18 +00:00
|
|
|
static int replace_page(struct vm_area_struct *vma, struct page *page,
|
|
|
|
struct page *kpage, pte_t orig_pte)
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
{
|
|
|
|
struct mm_struct *mm = vma->vm_mm;
|
|
|
|
pmd_t *pmd;
|
|
|
|
pte_t *ptep;
|
|
|
|
spinlock_t *ptl;
|
|
|
|
unsigned long addr;
|
|
|
|
int err = -EFAULT;
|
2012-10-08 23:33:35 +00:00
|
|
|
unsigned long mmun_start; /* For mmu_notifiers */
|
|
|
|
unsigned long mmun_end; /* For mmu_notifiers */
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
2009-12-15 01:59:18 +00:00
|
|
|
addr = page_address_in_vma(page, vma);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
if (addr == -EFAULT)
|
|
|
|
goto out;
|
|
|
|
|
2012-12-12 00:00:37 +00:00
|
|
|
pmd = mm_find_pmd(mm, addr);
|
|
|
|
if (!pmd)
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
goto out;
|
2011-01-13 23:47:19 +00:00
|
|
|
BUG_ON(pmd_trans_huge(*pmd));
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
2012-10-08 23:33:35 +00:00
|
|
|
mmun_start = addr;
|
|
|
|
mmun_end = addr + PAGE_SIZE;
|
|
|
|
mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
|
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
|
|
|
|
if (!pte_same(*ptep, orig_pte)) {
|
|
|
|
pte_unmap_unlock(ptep, ptl);
|
2012-10-08 23:33:35 +00:00
|
|
|
goto out_mn;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
|
|
|
|
2009-12-15 01:59:18 +00:00
|
|
|
get_page(kpage);
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
page_add_anon_rmap(kpage, vma, addr);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
|
|
|
flush_cache_page(vma, addr, pte_pfn(*ptep));
|
|
|
|
ptep_clear_flush(vma, addr, ptep);
|
2009-12-15 01:59:18 +00:00
|
|
|
set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
2009-12-15 01:59:18 +00:00
|
|
|
page_remove_rmap(page);
|
2011-01-13 23:46:28 +00:00
|
|
|
if (!page_mapped(page))
|
|
|
|
try_to_free_swap(page);
|
2009-12-15 01:59:18 +00:00
|
|
|
put_page(page);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
|
|
|
pte_unmap_unlock(ptep, ptl);
|
|
|
|
err = 0;
|
2012-10-08 23:33:35 +00:00
|
|
|
out_mn:
|
|
|
|
mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
out:
|
|
|
|
return err;
|
|
|
|
}
|
|
|
|
|
2011-01-13 23:47:19 +00:00
|
|
|
static int page_trans_compound_anon_split(struct page *page)
|
|
|
|
{
|
|
|
|
int ret = 0;
|
|
|
|
struct page *transhuge_head = page_trans_compound_anon(page);
|
|
|
|
if (transhuge_head) {
|
|
|
|
/* Get the reference on the head to split it. */
|
|
|
|
if (get_page_unless_zero(transhuge_head)) {
|
|
|
|
/*
|
|
|
|
* Recheck we got the reference while the head
|
|
|
|
* was still anonymous.
|
|
|
|
*/
|
|
|
|
if (PageAnon(transhuge_head))
|
|
|
|
ret = split_huge_page(transhuge_head);
|
|
|
|
else
|
|
|
|
/*
|
|
|
|
* Retry later if split_huge_page run
|
|
|
|
* from under us.
|
|
|
|
*/
|
|
|
|
ret = 1;
|
|
|
|
put_page(transhuge_head);
|
|
|
|
} else
|
|
|
|
/* Retry later if split_huge_page run from under us. */
|
|
|
|
ret = 1;
|
|
|
|
}
|
|
|
|
return ret;
|
|
|
|
}
|
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
/*
|
|
|
|
* try_to_merge_one_page - take two pages and merge them into one
|
2009-12-15 01:59:18 +00:00
|
|
|
* @vma: the vma that holds the pte pointing to page
|
|
|
|
* @page: the PageAnon page that we want to replace with kpage
|
2009-12-15 01:59:29 +00:00
|
|
|
* @kpage: the PageKsm page that we want to map instead of page,
|
|
|
|
* or NULL the first time when we want to use page as kpage.
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
*
|
|
|
|
* This function returns 0 if the pages were merged, -EFAULT otherwise.
|
|
|
|
*/
|
|
|
|
static int try_to_merge_one_page(struct vm_area_struct *vma,
|
2009-12-15 01:59:18 +00:00
|
|
|
struct page *page, struct page *kpage)
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
{
|
|
|
|
pte_t orig_pte = __pte(0);
|
|
|
|
int err = -EFAULT;
|
|
|
|
|
2009-12-15 01:59:25 +00:00
|
|
|
if (page == kpage) /* ksm page forked */
|
|
|
|
return 0;
|
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
if (!(vma->vm_flags & VM_MERGEABLE))
|
|
|
|
goto out;
|
2011-01-13 23:47:19 +00:00
|
|
|
if (PageTransCompound(page) && page_trans_compound_anon_split(page))
|
|
|
|
goto out;
|
|
|
|
BUG_ON(PageTransCompound(page));
|
2009-12-15 01:59:18 +00:00
|
|
|
if (!PageAnon(page))
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
goto out;
|
|
|
|
|
|
|
|
/*
|
|
|
|
* We need the page lock to read a stable PageSwapCache in
|
|
|
|
* write_protect_page(). We use trylock_page() instead of
|
|
|
|
* lock_page() because we don't want to wait here - we
|
|
|
|
* prefer to continue scanning and merging different pages,
|
|
|
|
* then come back to this page when it is unlocked.
|
|
|
|
*/
|
2009-12-15 01:59:18 +00:00
|
|
|
if (!trylock_page(page))
|
2009-12-15 01:59:17 +00:00
|
|
|
goto out;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
/*
|
|
|
|
* If this anonymous page is mapped only here, its pte may need
|
|
|
|
* to be write-protected. If it's mapped elsewhere, all of its
|
|
|
|
* ptes are necessarily already write-protected. But in either
|
|
|
|
* case, we need to lock and check page_count is not raised.
|
|
|
|
*/
|
2009-12-15 01:59:29 +00:00
|
|
|
if (write_protect_page(vma, page, &orig_pte) == 0) {
|
|
|
|
if (!kpage) {
|
|
|
|
/*
|
|
|
|
* While we hold page lock, upgrade page from
|
|
|
|
* PageAnon+anon_vma to PageKsm+NULL stable_node:
|
|
|
|
* stable_tree_insert() will update stable_node.
|
|
|
|
*/
|
|
|
|
set_page_stable_node(page, NULL);
|
|
|
|
mark_page_accessed(page);
|
|
|
|
err = 0;
|
|
|
|
} else if (pages_identical(page, kpage))
|
|
|
|
err = replace_page(vma, page, kpage, orig_pte);
|
|
|
|
}
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
2009-12-15 01:59:29 +00:00
|
|
|
if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
|
2009-12-15 01:59:22 +00:00
|
|
|
munlock_vma_page(page);
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
if (!PageMlocked(kpage)) {
|
|
|
|
unlock_page(page);
|
|
|
|
lock_page(kpage);
|
|
|
|
mlock_vma_page(kpage);
|
|
|
|
page = kpage; /* for final unlock */
|
|
|
|
}
|
|
|
|
}
|
2009-12-15 01:59:22 +00:00
|
|
|
|
2009-12-15 01:59:18 +00:00
|
|
|
unlock_page(page);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
out:
|
|
|
|
return err;
|
|
|
|
}
|
|
|
|
|
2009-09-22 00:02:15 +00:00
|
|
|
/*
|
|
|
|
* try_to_merge_with_ksm_page - like try_to_merge_two_pages,
|
|
|
|
* but no new kernel page is allocated: kpage must already be a ksm page.
|
2009-12-15 01:59:18 +00:00
|
|
|
*
|
|
|
|
* This function returns 0 if the pages were merged, -EFAULT otherwise.
|
2009-09-22 00:02:15 +00:00
|
|
|
*/
|
2009-12-15 01:59:18 +00:00
|
|
|
static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
|
|
|
|
struct page *page, struct page *kpage)
|
2009-09-22 00:02:15 +00:00
|
|
|
{
|
2009-12-15 01:59:18 +00:00
|
|
|
struct mm_struct *mm = rmap_item->mm;
|
2009-09-22 00:02:15 +00:00
|
|
|
struct vm_area_struct *vma;
|
|
|
|
int err = -EFAULT;
|
|
|
|
|
2009-12-15 01:59:18 +00:00
|
|
|
down_read(&mm->mmap_sem);
|
|
|
|
if (ksm_test_exit(mm))
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
goto out;
|
2009-12-15 01:59:18 +00:00
|
|
|
vma = find_vma(mm, rmap_item->address);
|
|
|
|
if (!vma || vma->vm_start > rmap_item->address)
|
2009-09-22 00:02:15 +00:00
|
|
|
goto out;
|
|
|
|
|
2009-12-15 01:59:18 +00:00
|
|
|
err = try_to_merge_one_page(vma, page, kpage);
|
2009-12-15 01:59:25 +00:00
|
|
|
if (err)
|
|
|
|
goto out;
|
|
|
|
|
|
|
|
/* Must get reference to anon_vma while still holding mmap_sem */
|
2011-03-22 23:32:46 +00:00
|
|
|
rmap_item->anon_vma = vma->anon_vma;
|
|
|
|
get_anon_vma(vma->anon_vma);
|
2009-09-22 00:02:15 +00:00
|
|
|
out:
|
2009-12-15 01:59:18 +00:00
|
|
|
up_read(&mm->mmap_sem);
|
2009-09-22 00:02:15 +00:00
|
|
|
return err;
|
|
|
|
}
|
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
/*
|
|
|
|
* try_to_merge_two_pages - take two identical pages and prepare them
|
|
|
|
* to be merged into one page.
|
|
|
|
*
|
2009-12-15 01:59:18 +00:00
|
|
|
* This function returns the kpage if we successfully merged two identical
|
|
|
|
* pages into one ksm page, NULL otherwise.
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
*
|
2009-12-15 01:59:29 +00:00
|
|
|
* Note that this function upgrades page to ksm page: if one of the pages
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
* is already a ksm page, try_to_merge_with_ksm_page should be used.
|
|
|
|
*/
|
2009-12-15 01:59:18 +00:00
|
|
|
static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
|
|
|
|
struct page *page,
|
|
|
|
struct rmap_item *tree_rmap_item,
|
|
|
|
struct page *tree_page)
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
{
|
2009-12-15 01:59:29 +00:00
|
|
|
int err;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
2009-12-15 01:59:29 +00:00
|
|
|
err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
if (!err) {
|
2009-12-15 01:59:18 +00:00
|
|
|
err = try_to_merge_with_ksm_page(tree_rmap_item,
|
2009-12-15 01:59:29 +00:00
|
|
|
tree_page, page);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
/*
|
2009-09-22 00:02:15 +00:00
|
|
|
* If that fails, we have a ksm page with only one pte
|
|
|
|
* pointing to it: so break it.
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
*/
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
if (err)
|
2009-12-15 01:59:18 +00:00
|
|
|
break_cow(rmap_item);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
2009-12-15 01:59:29 +00:00
|
|
|
return err ? NULL : page;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
2009-12-15 01:59:18 +00:00
|
|
|
* stable_tree_search - search for page inside the stable tree
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
*
|
|
|
|
* This function checks if there is a page inside the stable tree
|
|
|
|
* with identical content to the page that we are scanning right now.
|
|
|
|
*
|
2009-12-15 01:59:20 +00:00
|
|
|
* This function returns the stable tree node of identical content if found,
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
* NULL otherwise.
|
|
|
|
*/
|
ksm: memory hotremove migration only
The previous patch enables page migration of ksm pages, but that soon gets
into trouble: not surprising, since we're using the ksm page lock to lock
operations on its stable_node, but page migration switches the page whose
lock is to be used for that. Another layer of locking would fix it, but
do we need that yet?
Do we actually need page migration of ksm pages? Yes, memory hotremove
needs to offline sections of memory: and since we stopped allocating ksm
pages with GFP_HIGHUSER, they will tend to be GFP_HIGHUSER_MOVABLE
candidates for migration.
But KSM is currently unconscious of NUMA issues, happily merging pages
from different NUMA nodes: at present the rule must be, not to use
MADV_MERGEABLE where you care about NUMA. So no, NUMA page migration of
ksm pages does not make sense yet.
So, to complete support for ksm swapping we need to make hotremove safe.
ksm_memory_callback() take ksm_thread_mutex when MEM_GOING_OFFLINE and
release it when MEM_OFFLINE or MEM_CANCEL_OFFLINE. But if mapped pages
are freed before migration reaches them, stable_nodes may be left still
pointing to struct pages which have been removed from the system: the
stable_node needs to identify a page by pfn rather than page pointer, then
it can safely prune them when MEM_OFFLINE.
And make NUMA migration skip PageKsm pages where it skips PageReserved.
But it's only when we reach unmap_and_move() that the page lock is taken
and we can be sure that raised pagecount has prevented a PageAnon from
being upgraded: so add offlining arg to migrate_pages(), to migrate ksm
page when offlining (has sufficient locking) but reject it otherwise.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:33 +00:00
|
|
|
static struct page *stable_tree_search(struct page *page)
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
{
|
|
|
|
struct rb_node *node = root_stable_tree.rb_node;
|
2009-12-15 01:59:20 +00:00
|
|
|
struct stable_node *stable_node;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
2009-12-15 01:59:21 +00:00
|
|
|
stable_node = page_stable_node(page);
|
|
|
|
if (stable_node) { /* ksm page forked */
|
|
|
|
get_page(page);
|
ksm: memory hotremove migration only
The previous patch enables page migration of ksm pages, but that soon gets
into trouble: not surprising, since we're using the ksm page lock to lock
operations on its stable_node, but page migration switches the page whose
lock is to be used for that. Another layer of locking would fix it, but
do we need that yet?
Do we actually need page migration of ksm pages? Yes, memory hotremove
needs to offline sections of memory: and since we stopped allocating ksm
pages with GFP_HIGHUSER, they will tend to be GFP_HIGHUSER_MOVABLE
candidates for migration.
But KSM is currently unconscious of NUMA issues, happily merging pages
from different NUMA nodes: at present the rule must be, not to use
MADV_MERGEABLE where you care about NUMA. So no, NUMA page migration of
ksm pages does not make sense yet.
So, to complete support for ksm swapping we need to make hotremove safe.
ksm_memory_callback() take ksm_thread_mutex when MEM_GOING_OFFLINE and
release it when MEM_OFFLINE or MEM_CANCEL_OFFLINE. But if mapped pages
are freed before migration reaches them, stable_nodes may be left still
pointing to struct pages which have been removed from the system: the
stable_node needs to identify a page by pfn rather than page pointer, then
it can safely prune them when MEM_OFFLINE.
And make NUMA migration skip PageKsm pages where it skips PageReserved.
But it's only when we reach unmap_and_move() that the page lock is taken
and we can be sure that raised pagecount has prevented a PageAnon from
being upgraded: so add offlining arg to migrate_pages(), to migrate ksm
page when offlining (has sufficient locking) but reject it otherwise.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:33 +00:00
|
|
|
return page;
|
2009-12-15 01:59:21 +00:00
|
|
|
}
|
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
while (node) {
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
struct page *tree_page;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
int ret;
|
|
|
|
|
2009-12-15 01:59:21 +00:00
|
|
|
cond_resched();
|
2009-12-15 01:59:20 +00:00
|
|
|
stable_node = rb_entry(node, struct stable_node, node);
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
tree_page = get_ksm_page(stable_node);
|
|
|
|
if (!tree_page)
|
|
|
|
return NULL;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
ret = memcmp_pages(page, tree_page);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
if (ret < 0) {
|
|
|
|
put_page(tree_page);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
node = node->rb_left;
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
} else if (ret > 0) {
|
|
|
|
put_page(tree_page);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
node = node->rb_right;
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
} else
|
ksm: memory hotremove migration only
The previous patch enables page migration of ksm pages, but that soon gets
into trouble: not surprising, since we're using the ksm page lock to lock
operations on its stable_node, but page migration switches the page whose
lock is to be used for that. Another layer of locking would fix it, but
do we need that yet?
Do we actually need page migration of ksm pages? Yes, memory hotremove
needs to offline sections of memory: and since we stopped allocating ksm
pages with GFP_HIGHUSER, they will tend to be GFP_HIGHUSER_MOVABLE
candidates for migration.
But KSM is currently unconscious of NUMA issues, happily merging pages
from different NUMA nodes: at present the rule must be, not to use
MADV_MERGEABLE where you care about NUMA. So no, NUMA page migration of
ksm pages does not make sense yet.
So, to complete support for ksm swapping we need to make hotremove safe.
ksm_memory_callback() take ksm_thread_mutex when MEM_GOING_OFFLINE and
release it when MEM_OFFLINE or MEM_CANCEL_OFFLINE. But if mapped pages
are freed before migration reaches them, stable_nodes may be left still
pointing to struct pages which have been removed from the system: the
stable_node needs to identify a page by pfn rather than page pointer, then
it can safely prune them when MEM_OFFLINE.
And make NUMA migration skip PageKsm pages where it skips PageReserved.
But it's only when we reach unmap_and_move() that the page lock is taken
and we can be sure that raised pagecount has prevented a PageAnon from
being upgraded: so add offlining arg to migrate_pages(), to migrate ksm
page when offlining (has sufficient locking) but reject it otherwise.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:33 +00:00
|
|
|
return tree_page;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
return NULL;
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* stable_tree_insert - insert rmap_item pointing to new ksm page
|
|
|
|
* into the stable tree.
|
|
|
|
*
|
2009-12-15 01:59:20 +00:00
|
|
|
* This function returns the stable tree node just allocated on success,
|
|
|
|
* NULL otherwise.
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
*/
|
2009-12-15 01:59:20 +00:00
|
|
|
static struct stable_node *stable_tree_insert(struct page *kpage)
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
{
|
|
|
|
struct rb_node **new = &root_stable_tree.rb_node;
|
|
|
|
struct rb_node *parent = NULL;
|
2009-12-15 01:59:20 +00:00
|
|
|
struct stable_node *stable_node;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
|
|
|
while (*new) {
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
struct page *tree_page;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
int ret;
|
|
|
|
|
2009-12-15 01:59:21 +00:00
|
|
|
cond_resched();
|
2009-12-15 01:59:20 +00:00
|
|
|
stable_node = rb_entry(*new, struct stable_node, node);
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
tree_page = get_ksm_page(stable_node);
|
|
|
|
if (!tree_page)
|
|
|
|
return NULL;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
ret = memcmp_pages(kpage, tree_page);
|
|
|
|
put_page(tree_page);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
|
|
|
parent = *new;
|
|
|
|
if (ret < 0)
|
|
|
|
new = &parent->rb_left;
|
|
|
|
else if (ret > 0)
|
|
|
|
new = &parent->rb_right;
|
|
|
|
else {
|
|
|
|
/*
|
|
|
|
* It is not a bug that stable_tree_search() didn't
|
|
|
|
* find this node: because at that time our page was
|
|
|
|
* not yet write-protected, so may have changed since.
|
|
|
|
*/
|
|
|
|
return NULL;
|
|
|
|
}
|
|
|
|
}
|
|
|
|
|
2009-12-15 01:59:20 +00:00
|
|
|
stable_node = alloc_stable_node();
|
|
|
|
if (!stable_node)
|
|
|
|
return NULL;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
2009-12-15 01:59:20 +00:00
|
|
|
rb_link_node(&stable_node->node, parent, new);
|
|
|
|
rb_insert_color(&stable_node->node, &root_stable_tree);
|
|
|
|
|
|
|
|
INIT_HLIST_HEAD(&stable_node->hlist);
|
|
|
|
|
ksm: memory hotremove migration only
The previous patch enables page migration of ksm pages, but that soon gets
into trouble: not surprising, since we're using the ksm page lock to lock
operations on its stable_node, but page migration switches the page whose
lock is to be used for that. Another layer of locking would fix it, but
do we need that yet?
Do we actually need page migration of ksm pages? Yes, memory hotremove
needs to offline sections of memory: and since we stopped allocating ksm
pages with GFP_HIGHUSER, they will tend to be GFP_HIGHUSER_MOVABLE
candidates for migration.
But KSM is currently unconscious of NUMA issues, happily merging pages
from different NUMA nodes: at present the rule must be, not to use
MADV_MERGEABLE where you care about NUMA. So no, NUMA page migration of
ksm pages does not make sense yet.
So, to complete support for ksm swapping we need to make hotremove safe.
ksm_memory_callback() take ksm_thread_mutex when MEM_GOING_OFFLINE and
release it when MEM_OFFLINE or MEM_CANCEL_OFFLINE. But if mapped pages
are freed before migration reaches them, stable_nodes may be left still
pointing to struct pages which have been removed from the system: the
stable_node needs to identify a page by pfn rather than page pointer, then
it can safely prune them when MEM_OFFLINE.
And make NUMA migration skip PageKsm pages where it skips PageReserved.
But it's only when we reach unmap_and_move() that the page lock is taken
and we can be sure that raised pagecount has prevented a PageAnon from
being upgraded: so add offlining arg to migrate_pages(), to migrate ksm
page when offlining (has sufficient locking) but reject it otherwise.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:33 +00:00
|
|
|
stable_node->kpfn = page_to_pfn(kpage);
|
2009-12-15 01:59:21 +00:00
|
|
|
set_page_stable_node(kpage, stable_node);
|
|
|
|
|
2009-12-15 01:59:20 +00:00
|
|
|
return stable_node;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
2009-12-15 01:59:18 +00:00
|
|
|
* unstable_tree_search_insert - search for identical page,
|
|
|
|
* else insert rmap_item into the unstable tree.
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
*
|
|
|
|
* This function searches for a page in the unstable tree identical to the
|
|
|
|
* page currently being scanned; and if no identical page is found in the
|
|
|
|
* tree, we insert rmap_item as a new object into the unstable tree.
|
|
|
|
*
|
|
|
|
* This function returns pointer to rmap_item found to be identical
|
|
|
|
* to the currently scanned page, NULL otherwise.
|
|
|
|
*
|
|
|
|
* This function does both searching and inserting, because they share
|
|
|
|
* the same walking algorithm in an rbtree.
|
|
|
|
*/
|
2009-12-15 01:59:18 +00:00
|
|
|
static
|
|
|
|
struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
|
|
|
|
struct page *page,
|
|
|
|
struct page **tree_pagep)
|
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
{
|
|
|
|
struct rb_node **new = &root_unstable_tree.rb_node;
|
|
|
|
struct rb_node *parent = NULL;
|
|
|
|
|
|
|
|
while (*new) {
|
|
|
|
struct rmap_item *tree_rmap_item;
|
2009-12-15 01:59:18 +00:00
|
|
|
struct page *tree_page;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
int ret;
|
|
|
|
|
2009-11-09 15:58:23 +00:00
|
|
|
cond_resched();
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
tree_rmap_item = rb_entry(*new, struct rmap_item, node);
|
2009-12-15 01:59:18 +00:00
|
|
|
tree_page = get_mergeable_page(tree_rmap_item);
|
2010-04-23 17:18:10 +00:00
|
|
|
if (IS_ERR_OR_NULL(tree_page))
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
return NULL;
|
|
|
|
|
|
|
|
/*
|
2009-12-15 01:59:18 +00:00
|
|
|
* Don't substitute a ksm page for a forked page.
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
*/
|
2009-12-15 01:59:18 +00:00
|
|
|
if (page == tree_page) {
|
|
|
|
put_page(tree_page);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
return NULL;
|
|
|
|
}
|
|
|
|
|
2009-12-15 01:59:18 +00:00
|
|
|
ret = memcmp_pages(page, tree_page);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
|
|
|
parent = *new;
|
|
|
|
if (ret < 0) {
|
2009-12-15 01:59:18 +00:00
|
|
|
put_page(tree_page);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
new = &parent->rb_left;
|
|
|
|
} else if (ret > 0) {
|
2009-12-15 01:59:18 +00:00
|
|
|
put_page(tree_page);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
new = &parent->rb_right;
|
|
|
|
} else {
|
2009-12-15 01:59:18 +00:00
|
|
|
*tree_pagep = tree_page;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
return tree_rmap_item;
|
|
|
|
}
|
|
|
|
}
|
|
|
|
|
2009-12-15 01:59:20 +00:00
|
|
|
rmap_item->address |= UNSTABLE_FLAG;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
|
|
|
|
rb_link_node(&rmap_item->node, parent, new);
|
|
|
|
rb_insert_color(&rmap_item->node, &root_unstable_tree);
|
|
|
|
|
2009-09-22 00:02:11 +00:00
|
|
|
ksm_pages_unshared++;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
return NULL;
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
|
|
|
* stable_tree_append - add another rmap_item to the linked list of
|
|
|
|
* rmap_items hanging off a given node of the stable tree, all sharing
|
|
|
|
* the same ksm page.
|
|
|
|
*/
|
|
|
|
static void stable_tree_append(struct rmap_item *rmap_item,
|
2009-12-15 01:59:20 +00:00
|
|
|
struct stable_node *stable_node)
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
{
|
2009-12-15 01:59:20 +00:00
|
|
|
rmap_item->head = stable_node;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
rmap_item->address |= STABLE_FLAG;
|
2009-12-15 01:59:20 +00:00
|
|
|
hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
|
2009-09-22 00:02:10 +00:00
|
|
|
|
2009-12-15 01:59:20 +00:00
|
|
|
if (rmap_item->hlist.next)
|
|
|
|
ksm_pages_sharing++;
|
|
|
|
else
|
|
|
|
ksm_pages_shared++;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
2009-09-22 00:02:15 +00:00
|
|
|
* cmp_and_merge_page - first see if page can be merged into the stable tree;
|
|
|
|
* if not, compare checksum to previous and if it's the same, see if page can
|
|
|
|
* be inserted into the unstable tree, or merged with a page already there and
|
|
|
|
* both transferred to the stable tree.
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
*
|
|
|
|
* @page: the page that we are searching identical page to.
|
|
|
|
* @rmap_item: the reverse mapping into the virtual address of this page
|
|
|
|
*/
|
|
|
|
static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
|
|
|
|
{
|
|
|
|
struct rmap_item *tree_rmap_item;
|
2009-12-15 01:59:18 +00:00
|
|
|
struct page *tree_page = NULL;
|
2009-12-15 01:59:20 +00:00
|
|
|
struct stable_node *stable_node;
|
2009-12-15 01:59:18 +00:00
|
|
|
struct page *kpage;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
unsigned int checksum;
|
|
|
|
int err;
|
|
|
|
|
2009-12-15 01:59:16 +00:00
|
|
|
remove_rmap_item_from_tree(rmap_item);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
|
|
|
/* We first start with searching the page inside the stable tree */
|
ksm: memory hotremove migration only
The previous patch enables page migration of ksm pages, but that soon gets
into trouble: not surprising, since we're using the ksm page lock to lock
operations on its stable_node, but page migration switches the page whose
lock is to be used for that. Another layer of locking would fix it, but
do we need that yet?
Do we actually need page migration of ksm pages? Yes, memory hotremove
needs to offline sections of memory: and since we stopped allocating ksm
pages with GFP_HIGHUSER, they will tend to be GFP_HIGHUSER_MOVABLE
candidates for migration.
But KSM is currently unconscious of NUMA issues, happily merging pages
from different NUMA nodes: at present the rule must be, not to use
MADV_MERGEABLE where you care about NUMA. So no, NUMA page migration of
ksm pages does not make sense yet.
So, to complete support for ksm swapping we need to make hotremove safe.
ksm_memory_callback() take ksm_thread_mutex when MEM_GOING_OFFLINE and
release it when MEM_OFFLINE or MEM_CANCEL_OFFLINE. But if mapped pages
are freed before migration reaches them, stable_nodes may be left still
pointing to struct pages which have been removed from the system: the
stable_node needs to identify a page by pfn rather than page pointer, then
it can safely prune them when MEM_OFFLINE.
And make NUMA migration skip PageKsm pages where it skips PageReserved.
But it's only when we reach unmap_and_move() that the page lock is taken
and we can be sure that raised pagecount has prevented a PageAnon from
being upgraded: so add offlining arg to migrate_pages(), to migrate ksm
page when offlining (has sufficient locking) but reject it otherwise.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:33 +00:00
|
|
|
kpage = stable_tree_search(page);
|
|
|
|
if (kpage) {
|
2009-12-15 01:59:21 +00:00
|
|
|
err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
if (!err) {
|
|
|
|
/*
|
|
|
|
* The page was successfully merged:
|
|
|
|
* add its rmap_item to the stable tree.
|
|
|
|
*/
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
lock_page(kpage);
|
ksm: memory hotremove migration only
The previous patch enables page migration of ksm pages, but that soon gets
into trouble: not surprising, since we're using the ksm page lock to lock
operations on its stable_node, but page migration switches the page whose
lock is to be used for that. Another layer of locking would fix it, but
do we need that yet?
Do we actually need page migration of ksm pages? Yes, memory hotremove
needs to offline sections of memory: and since we stopped allocating ksm
pages with GFP_HIGHUSER, they will tend to be GFP_HIGHUSER_MOVABLE
candidates for migration.
But KSM is currently unconscious of NUMA issues, happily merging pages
from different NUMA nodes: at present the rule must be, not to use
MADV_MERGEABLE where you care about NUMA. So no, NUMA page migration of
ksm pages does not make sense yet.
So, to complete support for ksm swapping we need to make hotremove safe.
ksm_memory_callback() take ksm_thread_mutex when MEM_GOING_OFFLINE and
release it when MEM_OFFLINE or MEM_CANCEL_OFFLINE. But if mapped pages
are freed before migration reaches them, stable_nodes may be left still
pointing to struct pages which have been removed from the system: the
stable_node needs to identify a page by pfn rather than page pointer, then
it can safely prune them when MEM_OFFLINE.
And make NUMA migration skip PageKsm pages where it skips PageReserved.
But it's only when we reach unmap_and_move() that the page lock is taken
and we can be sure that raised pagecount has prevented a PageAnon from
being upgraded: so add offlining arg to migrate_pages(), to migrate ksm
page when offlining (has sufficient locking) but reject it otherwise.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:33 +00:00
|
|
|
stable_tree_append(rmap_item, page_stable_node(kpage));
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
unlock_page(kpage);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
2009-12-15 01:59:18 +00:00
|
|
|
put_page(kpage);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
return;
|
|
|
|
}
|
|
|
|
|
|
|
|
/*
|
ksm: take keyhole reference to page
There's a lamentable flaw in KSM swapping: the stable_node holds a
reference to the ksm page, so the page to be freed cannot actually be
freed until ksmd works its way around to removing the last rmap_item from
its stable_node. Which in some configurations may take minutes: not quite
responsive enough for memory reclaim. And we don't want to twist KSM and
its locking more tightly into the rest of mm. What a pity.
But although the stable_node needs to hold a pointer to the ksm page, does
it actually need to raise the reference count of that page?
No. It would need to do so if struct pages were ordinary kmalloc'ed
objects; but they are more stable than that, and reused in particular ways
according to particular rules.
Access to stable_node from its pointer in struct page is no problem, so
long as we never free a stable_node before the ksm page itself has been
freed. Access to struct page from its pointer in stable_node: reintroduce
get_ksm_page(), and let that peep out through its keyhole (the stable_node
pointer to ksm page), to see if that struct page still holds the right key
to open it (the ksm page mapping pointer back to this stable_node).
This relies upon the established way in which free_hot_cold_page() sets an
anon (including ksm) page->mapping to NULL; and relies upon no other user
of a struct page to put something which looks like the original
stable_node pointer (with two low bits also set) into page->mapping. It
also needs get_page_unless_zero() technique pioneered by speculative
pagecache; and uses rcu_read_lock() to keep the guarantees that gives.
There are several drivers which put pointers of their own into page->
mapping; but none of those could coincide with our stable_node pointers,
since KSM won't free a stable_node until it sees that the page has gone.
The only problem case found is the pagetable spinlock USE_SPLIT_PTLOCKS
places in struct page (my own abuse): to accommodate GENERIC_LOCKBREAK's
break_lock on 32-bit, that spans both page->private and page->mapping.
Since break_lock is only 0 or 1, again no confusion for get_ksm_page().
But what of DEBUG_SPINLOCK on 64-bit bigendian? When owner_cpu is 3
(matching PageKsm low bits), it might see 0xdead4ead00000003 in page->
mapping, which might coincide? We could get around that by... but a
better answer is to suppress USE_SPLIT_PTLOCKS when DEBUG_SPINLOCK or
DEBUG_LOCK_ALLOC, to stop bloating sizeof(struct page) in their case -
already proposed in an earlier mm/Kconfig patch.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:27 +00:00
|
|
|
* If the hash value of the page has changed from the last time
|
|
|
|
* we calculated it, this page is changing frequently: therefore we
|
|
|
|
* don't want to insert it in the unstable tree, and we don't want
|
|
|
|
* to waste our time searching for something identical to it there.
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
*/
|
|
|
|
checksum = calc_checksum(page);
|
|
|
|
if (rmap_item->oldchecksum != checksum) {
|
|
|
|
rmap_item->oldchecksum = checksum;
|
|
|
|
return;
|
|
|
|
}
|
|
|
|
|
2009-12-15 01:59:18 +00:00
|
|
|
tree_rmap_item =
|
|
|
|
unstable_tree_search_insert(rmap_item, page, &tree_page);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
if (tree_rmap_item) {
|
2009-12-15 01:59:18 +00:00
|
|
|
kpage = try_to_merge_two_pages(rmap_item, page,
|
|
|
|
tree_rmap_item, tree_page);
|
|
|
|
put_page(tree_page);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
/*
|
|
|
|
* As soon as we merge this page, we want to remove the
|
|
|
|
* rmap_item of the page we have merged with from the unstable
|
|
|
|
* tree, and insert it instead as new node in the stable tree.
|
|
|
|
*/
|
2009-12-15 01:59:18 +00:00
|
|
|
if (kpage) {
|
2009-12-15 01:59:16 +00:00
|
|
|
remove_rmap_item_from_tree(tree_rmap_item);
|
2009-09-22 00:02:11 +00:00
|
|
|
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
lock_page(kpage);
|
2009-12-15 01:59:20 +00:00
|
|
|
stable_node = stable_tree_insert(kpage);
|
|
|
|
if (stable_node) {
|
|
|
|
stable_tree_append(tree_rmap_item, stable_node);
|
|
|
|
stable_tree_append(rmap_item, stable_node);
|
|
|
|
}
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
unlock_page(kpage);
|
2009-12-15 01:59:20 +00:00
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
/*
|
|
|
|
* If we fail to insert the page into the stable tree,
|
|
|
|
* we will have 2 virtual addresses that are pointing
|
|
|
|
* to a ksm page left outside the stable tree,
|
|
|
|
* in which case we need to break_cow on both.
|
|
|
|
*/
|
2009-12-15 01:59:20 +00:00
|
|
|
if (!stable_node) {
|
2009-12-15 01:59:18 +00:00
|
|
|
break_cow(tree_rmap_item);
|
|
|
|
break_cow(rmap_item);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
|
|
|
}
|
|
|
|
}
|
|
|
|
}
|
|
|
|
|
|
|
|
static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
|
2009-12-15 01:59:19 +00:00
|
|
|
struct rmap_item **rmap_list,
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
unsigned long addr)
|
|
|
|
{
|
|
|
|
struct rmap_item *rmap_item;
|
|
|
|
|
2009-12-15 01:59:19 +00:00
|
|
|
while (*rmap_list) {
|
|
|
|
rmap_item = *rmap_list;
|
2009-12-15 01:59:16 +00:00
|
|
|
if ((rmap_item->address & PAGE_MASK) == addr)
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
return rmap_item;
|
|
|
|
if (rmap_item->address > addr)
|
|
|
|
break;
|
2009-12-15 01:59:19 +00:00
|
|
|
*rmap_list = rmap_item->rmap_list;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
remove_rmap_item_from_tree(rmap_item);
|
|
|
|
free_rmap_item(rmap_item);
|
|
|
|
}
|
|
|
|
|
|
|
|
rmap_item = alloc_rmap_item();
|
|
|
|
if (rmap_item) {
|
|
|
|
/* It has already been zeroed */
|
|
|
|
rmap_item->mm = mm_slot->mm;
|
|
|
|
rmap_item->address = addr;
|
2009-12-15 01:59:19 +00:00
|
|
|
rmap_item->rmap_list = *rmap_list;
|
|
|
|
*rmap_list = rmap_item;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
|
|
|
return rmap_item;
|
|
|
|
}
|
|
|
|
|
|
|
|
static struct rmap_item *scan_get_next_rmap_item(struct page **page)
|
|
|
|
{
|
|
|
|
struct mm_struct *mm;
|
|
|
|
struct mm_slot *slot;
|
|
|
|
struct vm_area_struct *vma;
|
|
|
|
struct rmap_item *rmap_item;
|
|
|
|
|
|
|
|
if (list_empty(&ksm_mm_head.mm_list))
|
|
|
|
return NULL;
|
|
|
|
|
|
|
|
slot = ksm_scan.mm_slot;
|
|
|
|
if (slot == &ksm_mm_head) {
|
2011-01-13 23:47:29 +00:00
|
|
|
/*
|
|
|
|
* A number of pages can hang around indefinitely on per-cpu
|
|
|
|
* pagevecs, raised page count preventing write_protect_page
|
|
|
|
* from merging them. Though it doesn't really matter much,
|
|
|
|
* it is puzzling to see some stuck in pages_volatile until
|
|
|
|
* other activity jostles them out, and they also prevented
|
|
|
|
* LTP's KSM test from succeeding deterministically; so drain
|
|
|
|
* them here (here rather than on entry to ksm_do_scan(),
|
|
|
|
* so we don't IPI too often when pages_to_scan is set low).
|
|
|
|
*/
|
|
|
|
lru_add_drain_all();
|
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
root_unstable_tree = RB_ROOT;
|
|
|
|
|
|
|
|
spin_lock(&ksm_mmlist_lock);
|
|
|
|
slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
|
|
|
|
ksm_scan.mm_slot = slot;
|
|
|
|
spin_unlock(&ksm_mmlist_lock);
|
2011-06-15 22:08:58 +00:00
|
|
|
/*
|
|
|
|
* Although we tested list_empty() above, a racing __ksm_exit
|
|
|
|
* of the last mm on the list may have removed it since then.
|
|
|
|
*/
|
|
|
|
if (slot == &ksm_mm_head)
|
|
|
|
return NULL;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
next_mm:
|
|
|
|
ksm_scan.address = 0;
|
2009-12-15 01:59:19 +00:00
|
|
|
ksm_scan.rmap_list = &slot->rmap_list;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
mm = slot->mm;
|
|
|
|
down_read(&mm->mmap_sem);
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
if (ksm_test_exit(mm))
|
|
|
|
vma = NULL;
|
|
|
|
else
|
|
|
|
vma = find_vma(mm, ksm_scan.address);
|
|
|
|
|
|
|
|
for (; vma; vma = vma->vm_next) {
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
if (!(vma->vm_flags & VM_MERGEABLE))
|
|
|
|
continue;
|
|
|
|
if (ksm_scan.address < vma->vm_start)
|
|
|
|
ksm_scan.address = vma->vm_start;
|
|
|
|
if (!vma->anon_vma)
|
|
|
|
ksm_scan.address = vma->vm_end;
|
|
|
|
|
|
|
|
while (ksm_scan.address < vma->vm_end) {
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
if (ksm_test_exit(mm))
|
|
|
|
break;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
*page = follow_page(vma, ksm_scan.address, FOLL_GET);
|
2011-01-13 23:47:00 +00:00
|
|
|
if (IS_ERR_OR_NULL(*page)) {
|
|
|
|
ksm_scan.address += PAGE_SIZE;
|
|
|
|
cond_resched();
|
|
|
|
continue;
|
|
|
|
}
|
2011-01-13 23:47:19 +00:00
|
|
|
if (PageAnon(*page) ||
|
|
|
|
page_trans_compound_anon(*page)) {
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
flush_anon_page(vma, *page, ksm_scan.address);
|
|
|
|
flush_dcache_page(*page);
|
|
|
|
rmap_item = get_next_rmap_item(slot,
|
2009-12-15 01:59:19 +00:00
|
|
|
ksm_scan.rmap_list, ksm_scan.address);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
if (rmap_item) {
|
2009-12-15 01:59:19 +00:00
|
|
|
ksm_scan.rmap_list =
|
|
|
|
&rmap_item->rmap_list;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
ksm_scan.address += PAGE_SIZE;
|
|
|
|
} else
|
|
|
|
put_page(*page);
|
|
|
|
up_read(&mm->mmap_sem);
|
|
|
|
return rmap_item;
|
|
|
|
}
|
2011-01-13 23:47:00 +00:00
|
|
|
put_page(*page);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
ksm_scan.address += PAGE_SIZE;
|
|
|
|
cond_resched();
|
|
|
|
}
|
|
|
|
}
|
|
|
|
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
if (ksm_test_exit(mm)) {
|
|
|
|
ksm_scan.address = 0;
|
2009-12-15 01:59:19 +00:00
|
|
|
ksm_scan.rmap_list = &slot->rmap_list;
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
}
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
/*
|
|
|
|
* Nuke all the rmap_items that are above this current rmap:
|
|
|
|
* because there were no VM_MERGEABLE vmas with such addresses.
|
|
|
|
*/
|
2009-12-15 01:59:19 +00:00
|
|
|
remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
|
|
|
spin_lock(&ksm_mmlist_lock);
|
2009-09-22 00:02:17 +00:00
|
|
|
ksm_scan.mm_slot = list_entry(slot->mm_list.next,
|
|
|
|
struct mm_slot, mm_list);
|
|
|
|
if (ksm_scan.address == 0) {
|
|
|
|
/*
|
|
|
|
* We've completed a full scan of all vmas, holding mmap_sem
|
|
|
|
* throughout, and found no VM_MERGEABLE: so do the same as
|
|
|
|
* __ksm_exit does to remove this mm from all our lists now.
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
* This applies either when cleaning up after __ksm_exit
|
|
|
|
* (but beware: we can reach here even before __ksm_exit),
|
|
|
|
* or when all VM_MERGEABLE areas have been unmapped (and
|
|
|
|
* mmap_sem then protects against race with MADV_MERGEABLE).
|
2009-09-22 00:02:17 +00:00
|
|
|
*/
|
|
|
|
hlist_del(&slot->link);
|
|
|
|
list_del(&slot->mm_list);
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
|
|
|
2009-09-22 00:02:17 +00:00
|
|
|
free_mm_slot(slot);
|
|
|
|
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
up_read(&mm->mmap_sem);
|
|
|
|
mmdrop(mm);
|
|
|
|
} else {
|
|
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
|
|
up_read(&mm->mmap_sem);
|
2009-09-22 00:02:17 +00:00
|
|
|
}
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
|
|
|
/* Repeat until we've completed scanning the whole list */
|
2009-09-22 00:02:17 +00:00
|
|
|
slot = ksm_scan.mm_slot;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
if (slot != &ksm_mm_head)
|
|
|
|
goto next_mm;
|
|
|
|
|
|
|
|
ksm_scan.seqnr++;
|
|
|
|
return NULL;
|
|
|
|
}
|
|
|
|
|
|
|
|
/**
|
|
|
|
* ksm_do_scan - the ksm scanner main worker function.
|
|
|
|
* @scan_npages - number of pages we want to scan before we return.
|
|
|
|
*/
|
|
|
|
static void ksm_do_scan(unsigned int scan_npages)
|
|
|
|
{
|
|
|
|
struct rmap_item *rmap_item;
|
2010-04-23 17:18:10 +00:00
|
|
|
struct page *uninitialized_var(page);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
2011-01-13 23:47:10 +00:00
|
|
|
while (scan_npages-- && likely(!freezing(current))) {
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
cond_resched();
|
|
|
|
rmap_item = scan_get_next_rmap_item(&page);
|
|
|
|
if (!rmap_item)
|
|
|
|
return;
|
|
|
|
if (!PageKsm(page) || !in_stable_tree(rmap_item))
|
|
|
|
cmp_and_merge_page(page, rmap_item);
|
|
|
|
put_page(page);
|
|
|
|
}
|
|
|
|
}
|
|
|
|
|
2009-09-22 00:02:14 +00:00
|
|
|
static int ksmd_should_run(void)
|
|
|
|
{
|
|
|
|
return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
|
|
|
|
}
|
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
static int ksm_scan_thread(void *nothing)
|
|
|
|
{
|
2011-01-13 23:47:10 +00:00
|
|
|
set_freezable();
|
2009-09-22 00:02:07 +00:00
|
|
|
set_user_nice(current, 5);
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
|
|
|
while (!kthread_should_stop()) {
|
2009-09-22 00:02:14 +00:00
|
|
|
mutex_lock(&ksm_thread_mutex);
|
|
|
|
if (ksmd_should_run())
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
ksm_do_scan(ksm_thread_pages_to_scan);
|
2009-09-22 00:02:14 +00:00
|
|
|
mutex_unlock(&ksm_thread_mutex);
|
|
|
|
|
2011-01-13 23:47:10 +00:00
|
|
|
try_to_freeze();
|
|
|
|
|
2009-09-22 00:02:14 +00:00
|
|
|
if (ksmd_should_run()) {
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
schedule_timeout_interruptible(
|
|
|
|
msecs_to_jiffies(ksm_thread_sleep_millisecs));
|
|
|
|
} else {
|
2011-01-13 23:47:10 +00:00
|
|
|
wait_event_freezable(ksm_thread_wait,
|
2009-09-22 00:02:14 +00:00
|
|
|
ksmd_should_run() || kthread_should_stop());
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
|
|
|
}
|
|
|
|
return 0;
|
|
|
|
}
|
|
|
|
|
2009-09-22 00:01:57 +00:00
|
|
|
int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
|
|
|
|
unsigned long end, int advice, unsigned long *vm_flags)
|
|
|
|
{
|
|
|
|
struct mm_struct *mm = vma->vm_mm;
|
2009-09-22 00:02:16 +00:00
|
|
|
int err;
|
2009-09-22 00:01:57 +00:00
|
|
|
|
|
|
|
switch (advice) {
|
|
|
|
case MADV_MERGEABLE:
|
|
|
|
/*
|
|
|
|
* Be somewhat over-protective for now!
|
|
|
|
*/
|
|
|
|
if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
|
|
|
|
VM_PFNMAP | VM_IO | VM_DONTEXPAND |
|
mm: kill vma flag VM_RESERVED and mm->reserved_vm counter
A long time ago, in v2.4, VM_RESERVED kept swapout process off VMA,
currently it lost original meaning but still has some effects:
| effect | alternative flags
-+------------------------+---------------------------------------------
1| account as reserved_vm | VM_IO
2| skip in core dump | VM_IO, VM_DONTDUMP
3| do not merge or expand | VM_IO, VM_DONTEXPAND, VM_HUGETLB, VM_PFNMAP
4| do not mlock | VM_IO, VM_DONTEXPAND, VM_HUGETLB, VM_PFNMAP
This patch removes reserved_vm counter from mm_struct. Seems like nobody
cares about it, it does not exported into userspace directly, it only
reduces total_vm showed in proc.
Thus VM_RESERVED can be replaced with VM_IO or pair VM_DONTEXPAND | VM_DONTDUMP.
remap_pfn_range() and io_remap_pfn_range() set VM_IO|VM_DONTEXPAND|VM_DONTDUMP.
remap_vmalloc_range() set VM_DONTEXPAND | VM_DONTDUMP.
[akpm@linux-foundation.org: drivers/vfio/pci/vfio_pci.c fixup]
Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Carsten Otte <cotte@de.ibm.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Eric Paris <eparis@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Morris <james.l.morris@oracle.com>
Cc: Jason Baron <jbaron@redhat.com>
Cc: Kentaro Takeda <takedakn@nttdata.co.jp>
Cc: Matt Helsley <matthltc@us.ibm.com>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Robert Richter <robert.richter@amd.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Venkatesh Pallipadi <venki@google.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:29:02 +00:00
|
|
|
VM_HUGETLB | VM_NONLINEAR | VM_MIXEDMAP))
|
2009-09-22 00:01:57 +00:00
|
|
|
return 0; /* just ignore the advice */
|
|
|
|
|
2012-10-08 23:28:37 +00:00
|
|
|
#ifdef VM_SAO
|
|
|
|
if (*vm_flags & VM_SAO)
|
|
|
|
return 0;
|
|
|
|
#endif
|
|
|
|
|
2009-09-22 00:02:16 +00:00
|
|
|
if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
|
|
|
|
err = __ksm_enter(mm);
|
|
|
|
if (err)
|
|
|
|
return err;
|
|
|
|
}
|
2009-09-22 00:01:57 +00:00
|
|
|
|
|
|
|
*vm_flags |= VM_MERGEABLE;
|
|
|
|
break;
|
|
|
|
|
|
|
|
case MADV_UNMERGEABLE:
|
|
|
|
if (!(*vm_flags & VM_MERGEABLE))
|
|
|
|
return 0; /* just ignore the advice */
|
|
|
|
|
2009-09-22 00:02:16 +00:00
|
|
|
if (vma->anon_vma) {
|
|
|
|
err = unmerge_ksm_pages(vma, start, end);
|
|
|
|
if (err)
|
|
|
|
return err;
|
|
|
|
}
|
2009-09-22 00:01:57 +00:00
|
|
|
|
|
|
|
*vm_flags &= ~VM_MERGEABLE;
|
|
|
|
break;
|
|
|
|
}
|
|
|
|
|
|
|
|
return 0;
|
|
|
|
}
|
|
|
|
|
|
|
|
int __ksm_enter(struct mm_struct *mm)
|
|
|
|
{
|
2009-09-22 00:02:14 +00:00
|
|
|
struct mm_slot *mm_slot;
|
|
|
|
int needs_wakeup;
|
|
|
|
|
|
|
|
mm_slot = alloc_mm_slot();
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
if (!mm_slot)
|
|
|
|
return -ENOMEM;
|
|
|
|
|
2009-09-22 00:02:14 +00:00
|
|
|
/* Check ksm_run too? Would need tighter locking */
|
|
|
|
needs_wakeup = list_empty(&ksm_mm_head.mm_list);
|
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
spin_lock(&ksm_mmlist_lock);
|
|
|
|
insert_to_mm_slots_hash(mm, mm_slot);
|
|
|
|
/*
|
|
|
|
* Insert just behind the scanning cursor, to let the area settle
|
|
|
|
* down a little; when fork is followed by immediate exec, we don't
|
|
|
|
* want ksmd to waste time setting up and tearing down an rmap_list.
|
|
|
|
*/
|
|
|
|
list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
|
|
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
|
|
|
2009-09-22 00:01:57 +00:00
|
|
|
set_bit(MMF_VM_MERGEABLE, &mm->flags);
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
atomic_inc(&mm->mm_count);
|
2009-09-22 00:02:14 +00:00
|
|
|
|
|
|
|
if (needs_wakeup)
|
|
|
|
wake_up_interruptible(&ksm_thread_wait);
|
|
|
|
|
2009-09-22 00:01:57 +00:00
|
|
|
return 0;
|
|
|
|
}
|
|
|
|
|
ksm: fix deadlock with munlock in exit_mmap
Rawhide users have reported hang at startup when cryptsetup is run: the
same problem can be simply reproduced by running a program int main() {
mlockall(MCL_CURRENT | MCL_FUTURE); return 0; }
The problem is that exit_mmap() applies munlock_vma_pages_all() to
clean up VM_LOCKED areas, and its current implementation (stupidly)
tries to fault in absent pages, for example where PROT_NONE prevented
them being faulted in when mlocking. Whereas the "ksm: fix oom
deadlock" patch, knowing there's a race by which KSM might try to fault
in pages after exit_mmap() had finally zapped the range, backs out of
such faults doing nothing when its ksm_test_exit() notices mm_users 0.
So revert that part of "ksm: fix oom deadlock" which moved the
ksm_exit() call from before exit_mmap() to the middle of exit_mmap();
and remove those ksm_test_exit() checks from the page fault paths, so
allowing the munlocking to proceed without interference.
ksm_exit, if there are rmap_items still chained on this mm slot, takes
mmap_sem write side: so preventing KSM from working on an mm while
exit_mmap runs. And KSM will bail out as soon as it notices that
mm_users is already zero, thanks to its internal ksm_test_exit checks.
So that when a task is killed by OOM killer or the user, KSM will not
indefinitely prevent it from running exit_mmap to release its memory.
This does break a part of what "ksm: fix oom deadlock" was trying to
achieve. When unmerging KSM (echo 2 >/sys/kernel/mm/ksm), and even
when ksmd itself has to cancel a KSM page, it is possible that the
first OOM-kill victim would be the KSM process being faulted: then its
memory won't be freed until a second victim has been selected (freeing
memory for the unmerging fault to complete).
But the OOM killer is already liable to kill a second victim once the
intended victim's p->mm goes to NULL: so there's not much point in
rejecting this KSM patch before fixing that OOM behaviour. It is very
much more important to allow KSM users to boot up, than to haggle over
an unlikely and poorly supported OOM case.
We also intend to fix munlocking to not fault pages: at which point
this patch _could_ be reverted; though that would be controversial, so
we hope to find a better solution.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Justin M. Forbes <jforbes@redhat.com>
Acked-for-now-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:22 +00:00
|
|
|
void __ksm_exit(struct mm_struct *mm)
|
2009-09-22 00:01:57 +00:00
|
|
|
{
|
2009-09-22 00:02:17 +00:00
|
|
|
struct mm_slot *mm_slot;
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
int easy_to_free = 0;
|
2009-09-22 00:02:17 +00:00
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
/*
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
* This process is exiting: if it's straightforward (as is the
|
|
|
|
* case when ksmd was never running), free mm_slot immediately.
|
|
|
|
* But if it's at the cursor or has rmap_items linked to it, use
|
|
|
|
* mmap_sem to synchronize with any break_cows before pagetables
|
|
|
|
* are freed, and leave the mm_slot on the list for ksmd to free.
|
|
|
|
* Beware: ksm may already have noticed it exiting and freed the slot.
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
*/
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
|
2009-09-22 00:02:17 +00:00
|
|
|
spin_lock(&ksm_mmlist_lock);
|
|
|
|
mm_slot = get_mm_slot(mm);
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
if (mm_slot && ksm_scan.mm_slot != mm_slot) {
|
2009-12-15 01:59:19 +00:00
|
|
|
if (!mm_slot->rmap_list) {
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
hlist_del(&mm_slot->link);
|
|
|
|
list_del(&mm_slot->mm_list);
|
|
|
|
easy_to_free = 1;
|
|
|
|
} else {
|
|
|
|
list_move(&mm_slot->mm_list,
|
|
|
|
&ksm_scan.mm_slot->mm_list);
|
|
|
|
}
|
2009-09-22 00:02:17 +00:00
|
|
|
}
|
|
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
|
|
|
ksm: fix oom deadlock
There's a now-obvious deadlock in KSM's out-of-memory handling:
imagine ksmd or KSM_RUN_UNMERGE handling, holding ksm_thread_mutex,
trying to allocate a page to break KSM in an mm which becomes the
OOM victim (quite likely in the unmerge case): it's killed and goes
to exit, and hangs there waiting to acquire ksm_thread_mutex.
Clearly we must not require ksm_thread_mutex in __ksm_exit, simple
though that made everything else: perhaps use mmap_sem somehow?
And part of the answer lies in the comments on unmerge_ksm_pages:
__ksm_exit should also leave all the rmap_item removal to ksmd.
But there's a fundamental problem, that KSM relies upon mmap_sem to
guarantee the consistency of the mm it's dealing with, yet exit_mmap
tears down an mm without taking mmap_sem. And bumping mm_users won't
help at all, that just ensures that the pages the OOM killer assumes
are on their way to being freed will not be freed.
The best answer seems to be, to move the ksm_exit callout from just
before exit_mmap, to the middle of exit_mmap: after the mm's pages
have been freed (if the mmu_gather is flushed), but before its page
tables and vma structures have been freed; and down_write,up_write
mmap_sem there to serialize with KSM's own reliance on mmap_sem.
But KSM then needs to be careful, whenever it downs mmap_sem, to
check that the mm is not already exiting: there's a danger of using
find_vma on a layout that's being torn apart, or writing into page
tables which have been freed for reuse; and even do_anonymous_page
and __do_fault need to check they're not being called by break_ksm
to reinstate a pte after zap_pte_range has zapped that page table.
Though it might be clearer to add an exiting flag, set while holding
mmap_sem in __ksm_exit, that wouldn't cover the issue of reinstating
a zapped pte. All we need is to check whether mm_users is 0 - but
must remember that ksmd may detect that before __ksm_exit is reached.
So, ksm_test_exit(mm) added to comment such checks on mm->mm_users.
__ksm_exit now has to leave clearing up the rmap_items to ksmd,
that needs ksm_thread_mutex; but shift the exiting mm just after the
ksm_scan cursor so that it will soon be dealt with. __ksm_enter raise
mm_count to hold the mm_struct, ksmd's exit processing (exactly like
its processing when it finds all VM_MERGEABLEs unmapped) mmdrop it,
similar procedure for KSM_RUN_UNMERGE (which has stopped ksmd).
But also give __ksm_exit a fast path: when there's no complication
(no rmap_items attached to mm and it's not at the ksm_scan cursor),
it can safely do all the exiting work itself. This is not just an
optimization: when ksmd is not running, the raised mm_count would
otherwise leak mm_structs.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:20 +00:00
|
|
|
if (easy_to_free) {
|
|
|
|
free_mm_slot(mm_slot);
|
|
|
|
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
|
|
|
|
mmdrop(mm);
|
|
|
|
} else if (mm_slot) {
|
|
|
|
down_write(&mm->mmap_sem);
|
|
|
|
up_write(&mm->mmap_sem);
|
|
|
|
}
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
|
|
|
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
struct page *ksm_does_need_to_copy(struct page *page,
|
|
|
|
struct vm_area_struct *vma, unsigned long address)
|
|
|
|
{
|
|
|
|
struct page *new_page;
|
|
|
|
|
|
|
|
new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
|
|
|
|
if (new_page) {
|
|
|
|
copy_user_highpage(new_page, page, address, vma);
|
|
|
|
|
|
|
|
SetPageDirty(new_page);
|
|
|
|
__SetPageUptodate(new_page);
|
|
|
|
SetPageSwapBacked(new_page);
|
|
|
|
__set_page_locked(new_page);
|
|
|
|
|
2012-10-08 23:33:18 +00:00
|
|
|
if (!mlocked_vma_newpage(vma, new_page))
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
|
|
|
|
else
|
|
|
|
add_page_to_unevictable_list(new_page);
|
|
|
|
}
|
|
|
|
|
|
|
|
return new_page;
|
|
|
|
}
|
|
|
|
|
|
|
|
int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
|
|
|
|
unsigned long *vm_flags)
|
|
|
|
{
|
|
|
|
struct stable_node *stable_node;
|
|
|
|
struct rmap_item *rmap_item;
|
|
|
|
struct hlist_node *hlist;
|
|
|
|
unsigned int mapcount = page_mapcount(page);
|
|
|
|
int referenced = 0;
|
2009-12-15 01:59:25 +00:00
|
|
|
int search_new_forks = 0;
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
|
|
|
|
VM_BUG_ON(!PageKsm(page));
|
|
|
|
VM_BUG_ON(!PageLocked(page));
|
|
|
|
|
|
|
|
stable_node = page_stable_node(page);
|
|
|
|
if (!stable_node)
|
|
|
|
return 0;
|
2009-12-15 01:59:25 +00:00
|
|
|
again:
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
|
2009-12-15 01:59:25 +00:00
|
|
|
struct anon_vma *anon_vma = rmap_item->anon_vma;
|
mm: change anon_vma linking to fix multi-process server scalability issue
The old anon_vma code can lead to scalability issues with heavily forking
workloads. Specifically, each anon_vma will be shared between the parent
process and all its child processes.
In a workload with 1000 child processes and a VMA with 1000 anonymous
pages per process that get COWed, this leads to a system with a million
anonymous pages in the same anon_vma, each of which is mapped in just one
of the 1000 processes. However, the current rmap code needs to walk them
all, leading to O(N) scanning complexity for each page.
This can result in systems where one CPU is walking the page tables of
1000 processes in page_referenced_one, while all other CPUs are stuck on
the anon_vma lock. This leads to catastrophic failure for a benchmark
like AIM7, where the total number of processes can reach in the tens of
thousands. Real workloads are still a factor 10 less process intensive
than AIM7, but they are catching up.
This patch changes the way anon_vmas and VMAs are linked, which allows us
to associate multiple anon_vmas with a VMA. At fork time, each child
process gets its own anon_vmas, in which its COWed pages will be
instantiated. The parents' anon_vma is also linked to the VMA, because
non-COWed pages could be present in any of the children.
This reduces rmap scanning complexity to O(1) for the pages of the 1000
child processes, with O(N) complexity for at most 1/N pages in the system.
This reduces the average scanning cost in heavily forking workloads from
O(N) to 2.
The only real complexity in this patch stems from the fact that linking a
VMA to anon_vmas now involves memory allocations. This means vma_adjust
can fail, if it needs to attach a VMA to anon_vma structures. This in
turn means error handling needs to be added to the calling functions.
A second source of complexity is that, because there can be multiple
anon_vmas, the anon_vma linking in vma_adjust can no longer be done under
"the" anon_vma lock. To prevent the rmap code from walking up an
incomplete VMA, this patch introduces the VM_LOCK_RMAP VMA flag. This bit
flag uses the same slot as the NOMMU VM_MAPPED_COPY, with an ifdef in mm.h
to make sure it is impossible to compile a kernel that needs both symbolic
values for the same bitflag.
Some test results:
Without the anon_vma changes, when AIM7 hits around 9.7k users (on a test
box with 16GB RAM and not quite enough IO), the system ends up running
>99% in system time, with every CPU on the same anon_vma lock in the
pageout code.
With these changes, AIM7 hits the cross-over point around 29.7k users.
This happens with ~99% IO wait time, there never seems to be any spike in
system time. The anon_vma lock contention appears to be resolved.
[akpm@linux-foundation.org: cleanups]
Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Larry Woodman <lwoodman@redhat.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-03-05 21:42:07 +00:00
|
|
|
struct anon_vma_chain *vmac;
|
2009-12-15 01:59:25 +00:00
|
|
|
struct vm_area_struct *vma;
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
|
2010-08-10 00:18:38 +00:00
|
|
|
anon_vma_lock(anon_vma);
|
mm anon rmap: replace same_anon_vma linked list with an interval tree.
When a large VMA (anon or private file mapping) is first touched, which
will populate its anon_vma field, and then split into many regions through
the use of mprotect(), the original anon_vma ends up linking all of the
vmas on a linked list. This can cause rmap to become inefficient, as we
have to walk potentially thousands of irrelevent vmas before finding the
one a given anon page might fall into.
By replacing the same_anon_vma linked list with an interval tree (where
each avc's interval is determined by its vma's start and last pgoffs), we
can make rmap efficient for this use case again.
While the change is large, all of its pieces are fairly simple.
Most places that were walking the same_anon_vma list were looking for a
known pgoff, so they can just use the anon_vma_interval_tree_foreach()
interval tree iterator instead. The exception here is ksm, where the
page's index is not known. It would probably be possible to rework ksm so
that the index would be known, but for now I have decided to keep things
simple and just walk the entirety of the interval tree there.
When updating vma's that already have an anon_vma assigned, we must take
care to re-index the corresponding avc's on their interval tree. This is
done through the use of anon_vma_interval_tree_pre_update_vma() and
anon_vma_interval_tree_post_update_vma(), which remove the avc's from
their interval tree before the update and re-insert them after the update.
The anon_vma stays locked during the update, so there is no chance that
rmap would miss the vmas that are being updated.
Signed-off-by: Michel Lespinasse <walken@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Daniel Santos <daniel.santos@pobox.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:31:39 +00:00
|
|
|
anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
|
|
|
|
0, ULONG_MAX) {
|
mm: change anon_vma linking to fix multi-process server scalability issue
The old anon_vma code can lead to scalability issues with heavily forking
workloads. Specifically, each anon_vma will be shared between the parent
process and all its child processes.
In a workload with 1000 child processes and a VMA with 1000 anonymous
pages per process that get COWed, this leads to a system with a million
anonymous pages in the same anon_vma, each of which is mapped in just one
of the 1000 processes. However, the current rmap code needs to walk them
all, leading to O(N) scanning complexity for each page.
This can result in systems where one CPU is walking the page tables of
1000 processes in page_referenced_one, while all other CPUs are stuck on
the anon_vma lock. This leads to catastrophic failure for a benchmark
like AIM7, where the total number of processes can reach in the tens of
thousands. Real workloads are still a factor 10 less process intensive
than AIM7, but they are catching up.
This patch changes the way anon_vmas and VMAs are linked, which allows us
to associate multiple anon_vmas with a VMA. At fork time, each child
process gets its own anon_vmas, in which its COWed pages will be
instantiated. The parents' anon_vma is also linked to the VMA, because
non-COWed pages could be present in any of the children.
This reduces rmap scanning complexity to O(1) for the pages of the 1000
child processes, with O(N) complexity for at most 1/N pages in the system.
This reduces the average scanning cost in heavily forking workloads from
O(N) to 2.
The only real complexity in this patch stems from the fact that linking a
VMA to anon_vmas now involves memory allocations. This means vma_adjust
can fail, if it needs to attach a VMA to anon_vma structures. This in
turn means error handling needs to be added to the calling functions.
A second source of complexity is that, because there can be multiple
anon_vmas, the anon_vma linking in vma_adjust can no longer be done under
"the" anon_vma lock. To prevent the rmap code from walking up an
incomplete VMA, this patch introduces the VM_LOCK_RMAP VMA flag. This bit
flag uses the same slot as the NOMMU VM_MAPPED_COPY, with an ifdef in mm.h
to make sure it is impossible to compile a kernel that needs both symbolic
values for the same bitflag.
Some test results:
Without the anon_vma changes, when AIM7 hits around 9.7k users (on a test
box with 16GB RAM and not quite enough IO), the system ends up running
>99% in system time, with every CPU on the same anon_vma lock in the
pageout code.
With these changes, AIM7 hits the cross-over point around 29.7k users.
This happens with ~99% IO wait time, there never seems to be any spike in
system time. The anon_vma lock contention appears to be resolved.
[akpm@linux-foundation.org: cleanups]
Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Larry Woodman <lwoodman@redhat.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-03-05 21:42:07 +00:00
|
|
|
vma = vmac->vma;
|
2009-12-15 01:59:25 +00:00
|
|
|
if (rmap_item->address < vma->vm_start ||
|
|
|
|
rmap_item->address >= vma->vm_end)
|
|
|
|
continue;
|
|
|
|
/*
|
|
|
|
* Initially we examine only the vma which covers this
|
|
|
|
* rmap_item; but later, if there is still work to do,
|
|
|
|
* we examine covering vmas in other mms: in case they
|
|
|
|
* were forked from the original since ksmd passed.
|
|
|
|
*/
|
|
|
|
if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
|
|
|
|
continue;
|
|
|
|
|
|
|
|
if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
|
|
|
|
continue;
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
|
2009-12-15 01:59:25 +00:00
|
|
|
referenced += page_referenced_one(page, vma,
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
rmap_item->address, &mapcount, vm_flags);
|
2009-12-15 01:59:25 +00:00
|
|
|
if (!search_new_forks || !mapcount)
|
|
|
|
break;
|
|
|
|
}
|
2010-08-10 00:18:38 +00:00
|
|
|
anon_vma_unlock(anon_vma);
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
if (!mapcount)
|
|
|
|
goto out;
|
|
|
|
}
|
2009-12-15 01:59:25 +00:00
|
|
|
if (!search_new_forks++)
|
|
|
|
goto again;
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
out:
|
|
|
|
return referenced;
|
|
|
|
}
|
|
|
|
|
|
|
|
int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
|
|
|
|
{
|
|
|
|
struct stable_node *stable_node;
|
|
|
|
struct hlist_node *hlist;
|
|
|
|
struct rmap_item *rmap_item;
|
|
|
|
int ret = SWAP_AGAIN;
|
2009-12-15 01:59:25 +00:00
|
|
|
int search_new_forks = 0;
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
|
|
|
|
VM_BUG_ON(!PageKsm(page));
|
|
|
|
VM_BUG_ON(!PageLocked(page));
|
|
|
|
|
|
|
|
stable_node = page_stable_node(page);
|
|
|
|
if (!stable_node)
|
|
|
|
return SWAP_FAIL;
|
2009-12-15 01:59:25 +00:00
|
|
|
again:
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
|
2009-12-15 01:59:25 +00:00
|
|
|
struct anon_vma *anon_vma = rmap_item->anon_vma;
|
mm: change anon_vma linking to fix multi-process server scalability issue
The old anon_vma code can lead to scalability issues with heavily forking
workloads. Specifically, each anon_vma will be shared between the parent
process and all its child processes.
In a workload with 1000 child processes and a VMA with 1000 anonymous
pages per process that get COWed, this leads to a system with a million
anonymous pages in the same anon_vma, each of which is mapped in just one
of the 1000 processes. However, the current rmap code needs to walk them
all, leading to O(N) scanning complexity for each page.
This can result in systems where one CPU is walking the page tables of
1000 processes in page_referenced_one, while all other CPUs are stuck on
the anon_vma lock. This leads to catastrophic failure for a benchmark
like AIM7, where the total number of processes can reach in the tens of
thousands. Real workloads are still a factor 10 less process intensive
than AIM7, but they are catching up.
This patch changes the way anon_vmas and VMAs are linked, which allows us
to associate multiple anon_vmas with a VMA. At fork time, each child
process gets its own anon_vmas, in which its COWed pages will be
instantiated. The parents' anon_vma is also linked to the VMA, because
non-COWed pages could be present in any of the children.
This reduces rmap scanning complexity to O(1) for the pages of the 1000
child processes, with O(N) complexity for at most 1/N pages in the system.
This reduces the average scanning cost in heavily forking workloads from
O(N) to 2.
The only real complexity in this patch stems from the fact that linking a
VMA to anon_vmas now involves memory allocations. This means vma_adjust
can fail, if it needs to attach a VMA to anon_vma structures. This in
turn means error handling needs to be added to the calling functions.
A second source of complexity is that, because there can be multiple
anon_vmas, the anon_vma linking in vma_adjust can no longer be done under
"the" anon_vma lock. To prevent the rmap code from walking up an
incomplete VMA, this patch introduces the VM_LOCK_RMAP VMA flag. This bit
flag uses the same slot as the NOMMU VM_MAPPED_COPY, with an ifdef in mm.h
to make sure it is impossible to compile a kernel that needs both symbolic
values for the same bitflag.
Some test results:
Without the anon_vma changes, when AIM7 hits around 9.7k users (on a test
box with 16GB RAM and not quite enough IO), the system ends up running
>99% in system time, with every CPU on the same anon_vma lock in the
pageout code.
With these changes, AIM7 hits the cross-over point around 29.7k users.
This happens with ~99% IO wait time, there never seems to be any spike in
system time. The anon_vma lock contention appears to be resolved.
[akpm@linux-foundation.org: cleanups]
Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Larry Woodman <lwoodman@redhat.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-03-05 21:42:07 +00:00
|
|
|
struct anon_vma_chain *vmac;
|
2009-12-15 01:59:25 +00:00
|
|
|
struct vm_area_struct *vma;
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
|
2010-08-10 00:18:38 +00:00
|
|
|
anon_vma_lock(anon_vma);
|
mm anon rmap: replace same_anon_vma linked list with an interval tree.
When a large VMA (anon or private file mapping) is first touched, which
will populate its anon_vma field, and then split into many regions through
the use of mprotect(), the original anon_vma ends up linking all of the
vmas on a linked list. This can cause rmap to become inefficient, as we
have to walk potentially thousands of irrelevent vmas before finding the
one a given anon page might fall into.
By replacing the same_anon_vma linked list with an interval tree (where
each avc's interval is determined by its vma's start and last pgoffs), we
can make rmap efficient for this use case again.
While the change is large, all of its pieces are fairly simple.
Most places that were walking the same_anon_vma list were looking for a
known pgoff, so they can just use the anon_vma_interval_tree_foreach()
interval tree iterator instead. The exception here is ksm, where the
page's index is not known. It would probably be possible to rework ksm so
that the index would be known, but for now I have decided to keep things
simple and just walk the entirety of the interval tree there.
When updating vma's that already have an anon_vma assigned, we must take
care to re-index the corresponding avc's on their interval tree. This is
done through the use of anon_vma_interval_tree_pre_update_vma() and
anon_vma_interval_tree_post_update_vma(), which remove the avc's from
their interval tree before the update and re-insert them after the update.
The anon_vma stays locked during the update, so there is no chance that
rmap would miss the vmas that are being updated.
Signed-off-by: Michel Lespinasse <walken@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Daniel Santos <daniel.santos@pobox.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:31:39 +00:00
|
|
|
anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
|
|
|
|
0, ULONG_MAX) {
|
mm: change anon_vma linking to fix multi-process server scalability issue
The old anon_vma code can lead to scalability issues with heavily forking
workloads. Specifically, each anon_vma will be shared between the parent
process and all its child processes.
In a workload with 1000 child processes and a VMA with 1000 anonymous
pages per process that get COWed, this leads to a system with a million
anonymous pages in the same anon_vma, each of which is mapped in just one
of the 1000 processes. However, the current rmap code needs to walk them
all, leading to O(N) scanning complexity for each page.
This can result in systems where one CPU is walking the page tables of
1000 processes in page_referenced_one, while all other CPUs are stuck on
the anon_vma lock. This leads to catastrophic failure for a benchmark
like AIM7, where the total number of processes can reach in the tens of
thousands. Real workloads are still a factor 10 less process intensive
than AIM7, but they are catching up.
This patch changes the way anon_vmas and VMAs are linked, which allows us
to associate multiple anon_vmas with a VMA. At fork time, each child
process gets its own anon_vmas, in which its COWed pages will be
instantiated. The parents' anon_vma is also linked to the VMA, because
non-COWed pages could be present in any of the children.
This reduces rmap scanning complexity to O(1) for the pages of the 1000
child processes, with O(N) complexity for at most 1/N pages in the system.
This reduces the average scanning cost in heavily forking workloads from
O(N) to 2.
The only real complexity in this patch stems from the fact that linking a
VMA to anon_vmas now involves memory allocations. This means vma_adjust
can fail, if it needs to attach a VMA to anon_vma structures. This in
turn means error handling needs to be added to the calling functions.
A second source of complexity is that, because there can be multiple
anon_vmas, the anon_vma linking in vma_adjust can no longer be done under
"the" anon_vma lock. To prevent the rmap code from walking up an
incomplete VMA, this patch introduces the VM_LOCK_RMAP VMA flag. This bit
flag uses the same slot as the NOMMU VM_MAPPED_COPY, with an ifdef in mm.h
to make sure it is impossible to compile a kernel that needs both symbolic
values for the same bitflag.
Some test results:
Without the anon_vma changes, when AIM7 hits around 9.7k users (on a test
box with 16GB RAM and not quite enough IO), the system ends up running
>99% in system time, with every CPU on the same anon_vma lock in the
pageout code.
With these changes, AIM7 hits the cross-over point around 29.7k users.
This happens with ~99% IO wait time, there never seems to be any spike in
system time. The anon_vma lock contention appears to be resolved.
[akpm@linux-foundation.org: cleanups]
Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Larry Woodman <lwoodman@redhat.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-03-05 21:42:07 +00:00
|
|
|
vma = vmac->vma;
|
2009-12-15 01:59:25 +00:00
|
|
|
if (rmap_item->address < vma->vm_start ||
|
|
|
|
rmap_item->address >= vma->vm_end)
|
|
|
|
continue;
|
|
|
|
/*
|
|
|
|
* Initially we examine only the vma which covers this
|
|
|
|
* rmap_item; but later, if there is still work to do,
|
|
|
|
* we examine covering vmas in other mms: in case they
|
|
|
|
* were forked from the original since ksmd passed.
|
|
|
|
*/
|
|
|
|
if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
|
|
|
|
continue;
|
|
|
|
|
|
|
|
ret = try_to_unmap_one(page, vma,
|
|
|
|
rmap_item->address, flags);
|
|
|
|
if (ret != SWAP_AGAIN || !page_mapped(page)) {
|
2010-08-10 00:18:38 +00:00
|
|
|
anon_vma_unlock(anon_vma);
|
2009-12-15 01:59:25 +00:00
|
|
|
goto out;
|
|
|
|
}
|
|
|
|
}
|
2010-08-10 00:18:38 +00:00
|
|
|
anon_vma_unlock(anon_vma);
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
}
|
2009-12-15 01:59:25 +00:00
|
|
|
if (!search_new_forks++)
|
|
|
|
goto again;
|
ksm: let shared pages be swappable
Initial implementation for swapping out KSM's shared pages: add
page_referenced_ksm() and try_to_unmap_ksm(), which rmap.c calls when
faced with a PageKsm page.
Most of what's needed can be got from the rmap_items listed from the
stable_node of the ksm page, without discovering the actual vma: so in
this patch just fake up a struct vma for page_referenced_one() or
try_to_unmap_one(), then refine that in the next patch.
Add VM_NONLINEAR to ksm_madvise()'s list of exclusions: it has always been
implicit there (being only set with VM_SHARED, already excluded), but
let's make it explicit, to help justify the lack of nonlinear unmap.
Rely on the page lock to protect against concurrent modifications to that
page's node of the stable tree.
The awkward part is not swapout but swapin: do_swap_page() and
page_add_anon_rmap() now have to allow for new possibilities - perhaps a
ksm page still in swapcache, perhaps a swapcache page associated with one
location in one anon_vma now needed for another location or anon_vma.
(And the vma might even be no longer VM_MERGEABLE when that happens.)
ksm_might_need_to_copy() checks for that case, and supplies a duplicate
page when necessary, simply leaving it to a subsequent pass of ksmd to
rediscover the identity and merge them back into one ksm page.
Disappointingly primitive: but the alternative would have to accumulate
unswappable info about the swapped out ksm pages, limiting swappability.
Remove page_add_ksm_rmap(): page_add_anon_rmap() now has to allow for the
particular case it was handling, so just use it instead.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:24 +00:00
|
|
|
out:
|
|
|
|
return ret;
|
|
|
|
}
|
|
|
|
|
ksm: rmap_walk to remove_migation_ptes
A side-effect of making ksm pages swappable is that they have to be placed
on the LRUs: which then exposes them to isolate_lru_page() and hence to
page migration.
Add rmap_walk() for remove_migration_ptes() to use: rmap_walk_anon() and
rmap_walk_file() in rmap.c, but rmap_walk_ksm() in ksm.c. Perhaps some
consolidation with existing code is possible, but don't attempt that yet
(try_to_unmap needs to handle nonlinears, but migration pte removal does
not).
rmap_walk() is sadly less general than it appears: rmap_walk_anon(), like
remove_anon_migration_ptes() which it replaces, avoids calling
page_lock_anon_vma(), because that includes a page_mapped() test which
fails when all migration ptes are in place. That was valid when NUMA page
migration was introduced (holding mmap_sem provided the missing guarantee
that anon_vma's slab had not already been destroyed), but I believe not
valid in the memory hotremove case added since.
For now do the same as before, and consider the best way to fix that
unlikely race later on. When fixed, we can probably use rmap_walk() on
hwpoisoned ksm pages too: for now, they remain among hwpoison's various
exceptions (its PageKsm test comes before the page is locked, but its
page_lock_anon_vma fails safely if an anon gets upgraded).
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:31 +00:00
|
|
|
#ifdef CONFIG_MIGRATION
|
|
|
|
int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
|
|
|
|
struct vm_area_struct *, unsigned long, void *), void *arg)
|
|
|
|
{
|
|
|
|
struct stable_node *stable_node;
|
|
|
|
struct hlist_node *hlist;
|
|
|
|
struct rmap_item *rmap_item;
|
|
|
|
int ret = SWAP_AGAIN;
|
|
|
|
int search_new_forks = 0;
|
|
|
|
|
|
|
|
VM_BUG_ON(!PageKsm(page));
|
|
|
|
VM_BUG_ON(!PageLocked(page));
|
|
|
|
|
|
|
|
stable_node = page_stable_node(page);
|
|
|
|
if (!stable_node)
|
|
|
|
return ret;
|
|
|
|
again:
|
|
|
|
hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
|
|
|
|
struct anon_vma *anon_vma = rmap_item->anon_vma;
|
mm: change anon_vma linking to fix multi-process server scalability issue
The old anon_vma code can lead to scalability issues with heavily forking
workloads. Specifically, each anon_vma will be shared between the parent
process and all its child processes.
In a workload with 1000 child processes and a VMA with 1000 anonymous
pages per process that get COWed, this leads to a system with a million
anonymous pages in the same anon_vma, each of which is mapped in just one
of the 1000 processes. However, the current rmap code needs to walk them
all, leading to O(N) scanning complexity for each page.
This can result in systems where one CPU is walking the page tables of
1000 processes in page_referenced_one, while all other CPUs are stuck on
the anon_vma lock. This leads to catastrophic failure for a benchmark
like AIM7, where the total number of processes can reach in the tens of
thousands. Real workloads are still a factor 10 less process intensive
than AIM7, but they are catching up.
This patch changes the way anon_vmas and VMAs are linked, which allows us
to associate multiple anon_vmas with a VMA. At fork time, each child
process gets its own anon_vmas, in which its COWed pages will be
instantiated. The parents' anon_vma is also linked to the VMA, because
non-COWed pages could be present in any of the children.
This reduces rmap scanning complexity to O(1) for the pages of the 1000
child processes, with O(N) complexity for at most 1/N pages in the system.
This reduces the average scanning cost in heavily forking workloads from
O(N) to 2.
The only real complexity in this patch stems from the fact that linking a
VMA to anon_vmas now involves memory allocations. This means vma_adjust
can fail, if it needs to attach a VMA to anon_vma structures. This in
turn means error handling needs to be added to the calling functions.
A second source of complexity is that, because there can be multiple
anon_vmas, the anon_vma linking in vma_adjust can no longer be done under
"the" anon_vma lock. To prevent the rmap code from walking up an
incomplete VMA, this patch introduces the VM_LOCK_RMAP VMA flag. This bit
flag uses the same slot as the NOMMU VM_MAPPED_COPY, with an ifdef in mm.h
to make sure it is impossible to compile a kernel that needs both symbolic
values for the same bitflag.
Some test results:
Without the anon_vma changes, when AIM7 hits around 9.7k users (on a test
box with 16GB RAM and not quite enough IO), the system ends up running
>99% in system time, with every CPU on the same anon_vma lock in the
pageout code.
With these changes, AIM7 hits the cross-over point around 29.7k users.
This happens with ~99% IO wait time, there never seems to be any spike in
system time. The anon_vma lock contention appears to be resolved.
[akpm@linux-foundation.org: cleanups]
Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Larry Woodman <lwoodman@redhat.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-03-05 21:42:07 +00:00
|
|
|
struct anon_vma_chain *vmac;
|
ksm: rmap_walk to remove_migation_ptes
A side-effect of making ksm pages swappable is that they have to be placed
on the LRUs: which then exposes them to isolate_lru_page() and hence to
page migration.
Add rmap_walk() for remove_migration_ptes() to use: rmap_walk_anon() and
rmap_walk_file() in rmap.c, but rmap_walk_ksm() in ksm.c. Perhaps some
consolidation with existing code is possible, but don't attempt that yet
(try_to_unmap needs to handle nonlinears, but migration pte removal does
not).
rmap_walk() is sadly less general than it appears: rmap_walk_anon(), like
remove_anon_migration_ptes() which it replaces, avoids calling
page_lock_anon_vma(), because that includes a page_mapped() test which
fails when all migration ptes are in place. That was valid when NUMA page
migration was introduced (holding mmap_sem provided the missing guarantee
that anon_vma's slab had not already been destroyed), but I believe not
valid in the memory hotremove case added since.
For now do the same as before, and consider the best way to fix that
unlikely race later on. When fixed, we can probably use rmap_walk() on
hwpoisoned ksm pages too: for now, they remain among hwpoison's various
exceptions (its PageKsm test comes before the page is locked, but its
page_lock_anon_vma fails safely if an anon gets upgraded).
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:31 +00:00
|
|
|
struct vm_area_struct *vma;
|
|
|
|
|
2010-08-10 00:18:38 +00:00
|
|
|
anon_vma_lock(anon_vma);
|
mm anon rmap: replace same_anon_vma linked list with an interval tree.
When a large VMA (anon or private file mapping) is first touched, which
will populate its anon_vma field, and then split into many regions through
the use of mprotect(), the original anon_vma ends up linking all of the
vmas on a linked list. This can cause rmap to become inefficient, as we
have to walk potentially thousands of irrelevent vmas before finding the
one a given anon page might fall into.
By replacing the same_anon_vma linked list with an interval tree (where
each avc's interval is determined by its vma's start and last pgoffs), we
can make rmap efficient for this use case again.
While the change is large, all of its pieces are fairly simple.
Most places that were walking the same_anon_vma list were looking for a
known pgoff, so they can just use the anon_vma_interval_tree_foreach()
interval tree iterator instead. The exception here is ksm, where the
page's index is not known. It would probably be possible to rework ksm so
that the index would be known, but for now I have decided to keep things
simple and just walk the entirety of the interval tree there.
When updating vma's that already have an anon_vma assigned, we must take
care to re-index the corresponding avc's on their interval tree. This is
done through the use of anon_vma_interval_tree_pre_update_vma() and
anon_vma_interval_tree_post_update_vma(), which remove the avc's from
their interval tree before the update and re-insert them after the update.
The anon_vma stays locked during the update, so there is no chance that
rmap would miss the vmas that are being updated.
Signed-off-by: Michel Lespinasse <walken@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Daniel Santos <daniel.santos@pobox.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-08 23:31:39 +00:00
|
|
|
anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
|
|
|
|
0, ULONG_MAX) {
|
mm: change anon_vma linking to fix multi-process server scalability issue
The old anon_vma code can lead to scalability issues with heavily forking
workloads. Specifically, each anon_vma will be shared between the parent
process and all its child processes.
In a workload with 1000 child processes and a VMA with 1000 anonymous
pages per process that get COWed, this leads to a system with a million
anonymous pages in the same anon_vma, each of which is mapped in just one
of the 1000 processes. However, the current rmap code needs to walk them
all, leading to O(N) scanning complexity for each page.
This can result in systems where one CPU is walking the page tables of
1000 processes in page_referenced_one, while all other CPUs are stuck on
the anon_vma lock. This leads to catastrophic failure for a benchmark
like AIM7, where the total number of processes can reach in the tens of
thousands. Real workloads are still a factor 10 less process intensive
than AIM7, but they are catching up.
This patch changes the way anon_vmas and VMAs are linked, which allows us
to associate multiple anon_vmas with a VMA. At fork time, each child
process gets its own anon_vmas, in which its COWed pages will be
instantiated. The parents' anon_vma is also linked to the VMA, because
non-COWed pages could be present in any of the children.
This reduces rmap scanning complexity to O(1) for the pages of the 1000
child processes, with O(N) complexity for at most 1/N pages in the system.
This reduces the average scanning cost in heavily forking workloads from
O(N) to 2.
The only real complexity in this patch stems from the fact that linking a
VMA to anon_vmas now involves memory allocations. This means vma_adjust
can fail, if it needs to attach a VMA to anon_vma structures. This in
turn means error handling needs to be added to the calling functions.
A second source of complexity is that, because there can be multiple
anon_vmas, the anon_vma linking in vma_adjust can no longer be done under
"the" anon_vma lock. To prevent the rmap code from walking up an
incomplete VMA, this patch introduces the VM_LOCK_RMAP VMA flag. This bit
flag uses the same slot as the NOMMU VM_MAPPED_COPY, with an ifdef in mm.h
to make sure it is impossible to compile a kernel that needs both symbolic
values for the same bitflag.
Some test results:
Without the anon_vma changes, when AIM7 hits around 9.7k users (on a test
box with 16GB RAM and not quite enough IO), the system ends up running
>99% in system time, with every CPU on the same anon_vma lock in the
pageout code.
With these changes, AIM7 hits the cross-over point around 29.7k users.
This happens with ~99% IO wait time, there never seems to be any spike in
system time. The anon_vma lock contention appears to be resolved.
[akpm@linux-foundation.org: cleanups]
Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Larry Woodman <lwoodman@redhat.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-03-05 21:42:07 +00:00
|
|
|
vma = vmac->vma;
|
ksm: rmap_walk to remove_migation_ptes
A side-effect of making ksm pages swappable is that they have to be placed
on the LRUs: which then exposes them to isolate_lru_page() and hence to
page migration.
Add rmap_walk() for remove_migration_ptes() to use: rmap_walk_anon() and
rmap_walk_file() in rmap.c, but rmap_walk_ksm() in ksm.c. Perhaps some
consolidation with existing code is possible, but don't attempt that yet
(try_to_unmap needs to handle nonlinears, but migration pte removal does
not).
rmap_walk() is sadly less general than it appears: rmap_walk_anon(), like
remove_anon_migration_ptes() which it replaces, avoids calling
page_lock_anon_vma(), because that includes a page_mapped() test which
fails when all migration ptes are in place. That was valid when NUMA page
migration was introduced (holding mmap_sem provided the missing guarantee
that anon_vma's slab had not already been destroyed), but I believe not
valid in the memory hotremove case added since.
For now do the same as before, and consider the best way to fix that
unlikely race later on. When fixed, we can probably use rmap_walk() on
hwpoisoned ksm pages too: for now, they remain among hwpoison's various
exceptions (its PageKsm test comes before the page is locked, but its
page_lock_anon_vma fails safely if an anon gets upgraded).
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:31 +00:00
|
|
|
if (rmap_item->address < vma->vm_start ||
|
|
|
|
rmap_item->address >= vma->vm_end)
|
|
|
|
continue;
|
|
|
|
/*
|
|
|
|
* Initially we examine only the vma which covers this
|
|
|
|
* rmap_item; but later, if there is still work to do,
|
|
|
|
* we examine covering vmas in other mms: in case they
|
|
|
|
* were forked from the original since ksmd passed.
|
|
|
|
*/
|
|
|
|
if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
|
|
|
|
continue;
|
|
|
|
|
|
|
|
ret = rmap_one(page, vma, rmap_item->address, arg);
|
|
|
|
if (ret != SWAP_AGAIN) {
|
2010-08-10 00:18:38 +00:00
|
|
|
anon_vma_unlock(anon_vma);
|
ksm: rmap_walk to remove_migation_ptes
A side-effect of making ksm pages swappable is that they have to be placed
on the LRUs: which then exposes them to isolate_lru_page() and hence to
page migration.
Add rmap_walk() for remove_migration_ptes() to use: rmap_walk_anon() and
rmap_walk_file() in rmap.c, but rmap_walk_ksm() in ksm.c. Perhaps some
consolidation with existing code is possible, but don't attempt that yet
(try_to_unmap needs to handle nonlinears, but migration pte removal does
not).
rmap_walk() is sadly less general than it appears: rmap_walk_anon(), like
remove_anon_migration_ptes() which it replaces, avoids calling
page_lock_anon_vma(), because that includes a page_mapped() test which
fails when all migration ptes are in place. That was valid when NUMA page
migration was introduced (holding mmap_sem provided the missing guarantee
that anon_vma's slab had not already been destroyed), but I believe not
valid in the memory hotremove case added since.
For now do the same as before, and consider the best way to fix that
unlikely race later on. When fixed, we can probably use rmap_walk() on
hwpoisoned ksm pages too: for now, they remain among hwpoison's various
exceptions (its PageKsm test comes before the page is locked, but its
page_lock_anon_vma fails safely if an anon gets upgraded).
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:31 +00:00
|
|
|
goto out;
|
|
|
|
}
|
|
|
|
}
|
2010-08-10 00:18:38 +00:00
|
|
|
anon_vma_unlock(anon_vma);
|
ksm: rmap_walk to remove_migation_ptes
A side-effect of making ksm pages swappable is that they have to be placed
on the LRUs: which then exposes them to isolate_lru_page() and hence to
page migration.
Add rmap_walk() for remove_migration_ptes() to use: rmap_walk_anon() and
rmap_walk_file() in rmap.c, but rmap_walk_ksm() in ksm.c. Perhaps some
consolidation with existing code is possible, but don't attempt that yet
(try_to_unmap needs to handle nonlinears, but migration pte removal does
not).
rmap_walk() is sadly less general than it appears: rmap_walk_anon(), like
remove_anon_migration_ptes() which it replaces, avoids calling
page_lock_anon_vma(), because that includes a page_mapped() test which
fails when all migration ptes are in place. That was valid when NUMA page
migration was introduced (holding mmap_sem provided the missing guarantee
that anon_vma's slab had not already been destroyed), but I believe not
valid in the memory hotremove case added since.
For now do the same as before, and consider the best way to fix that
unlikely race later on. When fixed, we can probably use rmap_walk() on
hwpoisoned ksm pages too: for now, they remain among hwpoison's various
exceptions (its PageKsm test comes before the page is locked, but its
page_lock_anon_vma fails safely if an anon gets upgraded).
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:31 +00:00
|
|
|
}
|
|
|
|
if (!search_new_forks++)
|
|
|
|
goto again;
|
|
|
|
out:
|
|
|
|
return ret;
|
|
|
|
}
|
|
|
|
|
|
|
|
void ksm_migrate_page(struct page *newpage, struct page *oldpage)
|
|
|
|
{
|
|
|
|
struct stable_node *stable_node;
|
|
|
|
|
|
|
|
VM_BUG_ON(!PageLocked(oldpage));
|
|
|
|
VM_BUG_ON(!PageLocked(newpage));
|
|
|
|
VM_BUG_ON(newpage->mapping != oldpage->mapping);
|
|
|
|
|
|
|
|
stable_node = page_stable_node(newpage);
|
|
|
|
if (stable_node) {
|
ksm: memory hotremove migration only
The previous patch enables page migration of ksm pages, but that soon gets
into trouble: not surprising, since we're using the ksm page lock to lock
operations on its stable_node, but page migration switches the page whose
lock is to be used for that. Another layer of locking would fix it, but
do we need that yet?
Do we actually need page migration of ksm pages? Yes, memory hotremove
needs to offline sections of memory: and since we stopped allocating ksm
pages with GFP_HIGHUSER, they will tend to be GFP_HIGHUSER_MOVABLE
candidates for migration.
But KSM is currently unconscious of NUMA issues, happily merging pages
from different NUMA nodes: at present the rule must be, not to use
MADV_MERGEABLE where you care about NUMA. So no, NUMA page migration of
ksm pages does not make sense yet.
So, to complete support for ksm swapping we need to make hotremove safe.
ksm_memory_callback() take ksm_thread_mutex when MEM_GOING_OFFLINE and
release it when MEM_OFFLINE or MEM_CANCEL_OFFLINE. But if mapped pages
are freed before migration reaches them, stable_nodes may be left still
pointing to struct pages which have been removed from the system: the
stable_node needs to identify a page by pfn rather than page pointer, then
it can safely prune them when MEM_OFFLINE.
And make NUMA migration skip PageKsm pages where it skips PageReserved.
But it's only when we reach unmap_and_move() that the page lock is taken
and we can be sure that raised pagecount has prevented a PageAnon from
being upgraded: so add offlining arg to migrate_pages(), to migrate ksm
page when offlining (has sufficient locking) but reject it otherwise.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:33 +00:00
|
|
|
VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
|
|
|
|
stable_node->kpfn = page_to_pfn(newpage);
|
ksm: rmap_walk to remove_migation_ptes
A side-effect of making ksm pages swappable is that they have to be placed
on the LRUs: which then exposes them to isolate_lru_page() and hence to
page migration.
Add rmap_walk() for remove_migration_ptes() to use: rmap_walk_anon() and
rmap_walk_file() in rmap.c, but rmap_walk_ksm() in ksm.c. Perhaps some
consolidation with existing code is possible, but don't attempt that yet
(try_to_unmap needs to handle nonlinears, but migration pte removal does
not).
rmap_walk() is sadly less general than it appears: rmap_walk_anon(), like
remove_anon_migration_ptes() which it replaces, avoids calling
page_lock_anon_vma(), because that includes a page_mapped() test which
fails when all migration ptes are in place. That was valid when NUMA page
migration was introduced (holding mmap_sem provided the missing guarantee
that anon_vma's slab had not already been destroyed), but I believe not
valid in the memory hotremove case added since.
For now do the same as before, and consider the best way to fix that
unlikely race later on. When fixed, we can probably use rmap_walk() on
hwpoisoned ksm pages too: for now, they remain among hwpoison's various
exceptions (its PageKsm test comes before the page is locked, but its
page_lock_anon_vma fails safely if an anon gets upgraded).
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:31 +00:00
|
|
|
}
|
|
|
|
}
|
|
|
|
#endif /* CONFIG_MIGRATION */
|
|
|
|
|
ksm: memory hotremove migration only
The previous patch enables page migration of ksm pages, but that soon gets
into trouble: not surprising, since we're using the ksm page lock to lock
operations on its stable_node, but page migration switches the page whose
lock is to be used for that. Another layer of locking would fix it, but
do we need that yet?
Do we actually need page migration of ksm pages? Yes, memory hotremove
needs to offline sections of memory: and since we stopped allocating ksm
pages with GFP_HIGHUSER, they will tend to be GFP_HIGHUSER_MOVABLE
candidates for migration.
But KSM is currently unconscious of NUMA issues, happily merging pages
from different NUMA nodes: at present the rule must be, not to use
MADV_MERGEABLE where you care about NUMA. So no, NUMA page migration of
ksm pages does not make sense yet.
So, to complete support for ksm swapping we need to make hotremove safe.
ksm_memory_callback() take ksm_thread_mutex when MEM_GOING_OFFLINE and
release it when MEM_OFFLINE or MEM_CANCEL_OFFLINE. But if mapped pages
are freed before migration reaches them, stable_nodes may be left still
pointing to struct pages which have been removed from the system: the
stable_node needs to identify a page by pfn rather than page pointer, then
it can safely prune them when MEM_OFFLINE.
And make NUMA migration skip PageKsm pages where it skips PageReserved.
But it's only when we reach unmap_and_move() that the page lock is taken
and we can be sure that raised pagecount has prevented a PageAnon from
being upgraded: so add offlining arg to migrate_pages(), to migrate ksm
page when offlining (has sufficient locking) but reject it otherwise.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:33 +00:00
|
|
|
#ifdef CONFIG_MEMORY_HOTREMOVE
|
|
|
|
static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
|
|
|
|
unsigned long end_pfn)
|
|
|
|
{
|
|
|
|
struct rb_node *node;
|
|
|
|
|
|
|
|
for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
|
|
|
|
struct stable_node *stable_node;
|
|
|
|
|
|
|
|
stable_node = rb_entry(node, struct stable_node, node);
|
|
|
|
if (stable_node->kpfn >= start_pfn &&
|
|
|
|
stable_node->kpfn < end_pfn)
|
|
|
|
return stable_node;
|
|
|
|
}
|
|
|
|
return NULL;
|
|
|
|
}
|
|
|
|
|
|
|
|
static int ksm_memory_callback(struct notifier_block *self,
|
|
|
|
unsigned long action, void *arg)
|
|
|
|
{
|
|
|
|
struct memory_notify *mn = arg;
|
|
|
|
struct stable_node *stable_node;
|
|
|
|
|
|
|
|
switch (action) {
|
|
|
|
case MEM_GOING_OFFLINE:
|
|
|
|
/*
|
|
|
|
* Keep it very simple for now: just lock out ksmd and
|
|
|
|
* MADV_UNMERGEABLE while any memory is going offline.
|
2010-12-02 22:31:20 +00:00
|
|
|
* mutex_lock_nested() is necessary because lockdep was alarmed
|
|
|
|
* that here we take ksm_thread_mutex inside notifier chain
|
|
|
|
* mutex, and later take notifier chain mutex inside
|
|
|
|
* ksm_thread_mutex to unlock it. But that's safe because both
|
|
|
|
* are inside mem_hotplug_mutex.
|
ksm: memory hotremove migration only
The previous patch enables page migration of ksm pages, but that soon gets
into trouble: not surprising, since we're using the ksm page lock to lock
operations on its stable_node, but page migration switches the page whose
lock is to be used for that. Another layer of locking would fix it, but
do we need that yet?
Do we actually need page migration of ksm pages? Yes, memory hotremove
needs to offline sections of memory: and since we stopped allocating ksm
pages with GFP_HIGHUSER, they will tend to be GFP_HIGHUSER_MOVABLE
candidates for migration.
But KSM is currently unconscious of NUMA issues, happily merging pages
from different NUMA nodes: at present the rule must be, not to use
MADV_MERGEABLE where you care about NUMA. So no, NUMA page migration of
ksm pages does not make sense yet.
So, to complete support for ksm swapping we need to make hotremove safe.
ksm_memory_callback() take ksm_thread_mutex when MEM_GOING_OFFLINE and
release it when MEM_OFFLINE or MEM_CANCEL_OFFLINE. But if mapped pages
are freed before migration reaches them, stable_nodes may be left still
pointing to struct pages which have been removed from the system: the
stable_node needs to identify a page by pfn rather than page pointer, then
it can safely prune them when MEM_OFFLINE.
And make NUMA migration skip PageKsm pages where it skips PageReserved.
But it's only when we reach unmap_and_move() that the page lock is taken
and we can be sure that raised pagecount has prevented a PageAnon from
being upgraded: so add offlining arg to migrate_pages(), to migrate ksm
page when offlining (has sufficient locking) but reject it otherwise.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:33 +00:00
|
|
|
*/
|
2010-12-02 22:31:20 +00:00
|
|
|
mutex_lock_nested(&ksm_thread_mutex, SINGLE_DEPTH_NESTING);
|
ksm: memory hotremove migration only
The previous patch enables page migration of ksm pages, but that soon gets
into trouble: not surprising, since we're using the ksm page lock to lock
operations on its stable_node, but page migration switches the page whose
lock is to be used for that. Another layer of locking would fix it, but
do we need that yet?
Do we actually need page migration of ksm pages? Yes, memory hotremove
needs to offline sections of memory: and since we stopped allocating ksm
pages with GFP_HIGHUSER, they will tend to be GFP_HIGHUSER_MOVABLE
candidates for migration.
But KSM is currently unconscious of NUMA issues, happily merging pages
from different NUMA nodes: at present the rule must be, not to use
MADV_MERGEABLE where you care about NUMA. So no, NUMA page migration of
ksm pages does not make sense yet.
So, to complete support for ksm swapping we need to make hotremove safe.
ksm_memory_callback() take ksm_thread_mutex when MEM_GOING_OFFLINE and
release it when MEM_OFFLINE or MEM_CANCEL_OFFLINE. But if mapped pages
are freed before migration reaches them, stable_nodes may be left still
pointing to struct pages which have been removed from the system: the
stable_node needs to identify a page by pfn rather than page pointer, then
it can safely prune them when MEM_OFFLINE.
And make NUMA migration skip PageKsm pages where it skips PageReserved.
But it's only when we reach unmap_and_move() that the page lock is taken
and we can be sure that raised pagecount has prevented a PageAnon from
being upgraded: so add offlining arg to migrate_pages(), to migrate ksm
page when offlining (has sufficient locking) but reject it otherwise.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:33 +00:00
|
|
|
break;
|
|
|
|
|
|
|
|
case MEM_OFFLINE:
|
|
|
|
/*
|
|
|
|
* Most of the work is done by page migration; but there might
|
|
|
|
* be a few stable_nodes left over, still pointing to struct
|
|
|
|
* pages which have been offlined: prune those from the tree.
|
|
|
|
*/
|
|
|
|
while ((stable_node = ksm_check_stable_tree(mn->start_pfn,
|
|
|
|
mn->start_pfn + mn->nr_pages)) != NULL)
|
|
|
|
remove_node_from_stable_tree(stable_node);
|
|
|
|
/* fallthrough */
|
|
|
|
|
|
|
|
case MEM_CANCEL_OFFLINE:
|
|
|
|
mutex_unlock(&ksm_thread_mutex);
|
|
|
|
break;
|
|
|
|
}
|
|
|
|
return NOTIFY_OK;
|
|
|
|
}
|
|
|
|
#endif /* CONFIG_MEMORY_HOTREMOVE */
|
|
|
|
|
2009-09-22 00:02:23 +00:00
|
|
|
#ifdef CONFIG_SYSFS
|
|
|
|
/*
|
|
|
|
* This all compiles without CONFIG_SYSFS, but is a waste of space.
|
|
|
|
*/
|
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
#define KSM_ATTR_RO(_name) \
|
|
|
|
static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
|
|
|
|
#define KSM_ATTR(_name) \
|
|
|
|
static struct kobj_attribute _name##_attr = \
|
|
|
|
__ATTR(_name, 0644, _name##_show, _name##_store)
|
|
|
|
|
|
|
|
static ssize_t sleep_millisecs_show(struct kobject *kobj,
|
|
|
|
struct kobj_attribute *attr, char *buf)
|
|
|
|
{
|
|
|
|
return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
|
|
|
|
}
|
|
|
|
|
|
|
|
static ssize_t sleep_millisecs_store(struct kobject *kobj,
|
|
|
|
struct kobj_attribute *attr,
|
|
|
|
const char *buf, size_t count)
|
|
|
|
{
|
|
|
|
unsigned long msecs;
|
|
|
|
int err;
|
|
|
|
|
|
|
|
err = strict_strtoul(buf, 10, &msecs);
|
|
|
|
if (err || msecs > UINT_MAX)
|
|
|
|
return -EINVAL;
|
|
|
|
|
|
|
|
ksm_thread_sleep_millisecs = msecs;
|
|
|
|
|
|
|
|
return count;
|
|
|
|
}
|
|
|
|
KSM_ATTR(sleep_millisecs);
|
|
|
|
|
|
|
|
static ssize_t pages_to_scan_show(struct kobject *kobj,
|
|
|
|
struct kobj_attribute *attr, char *buf)
|
|
|
|
{
|
|
|
|
return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
|
|
|
|
}
|
|
|
|
|
|
|
|
static ssize_t pages_to_scan_store(struct kobject *kobj,
|
|
|
|
struct kobj_attribute *attr,
|
|
|
|
const char *buf, size_t count)
|
|
|
|
{
|
|
|
|
int err;
|
|
|
|
unsigned long nr_pages;
|
|
|
|
|
|
|
|
err = strict_strtoul(buf, 10, &nr_pages);
|
|
|
|
if (err || nr_pages > UINT_MAX)
|
|
|
|
return -EINVAL;
|
|
|
|
|
|
|
|
ksm_thread_pages_to_scan = nr_pages;
|
|
|
|
|
|
|
|
return count;
|
|
|
|
}
|
|
|
|
KSM_ATTR(pages_to_scan);
|
|
|
|
|
|
|
|
static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
|
|
|
|
char *buf)
|
|
|
|
{
|
|
|
|
return sprintf(buf, "%u\n", ksm_run);
|
|
|
|
}
|
|
|
|
|
|
|
|
static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
|
|
|
|
const char *buf, size_t count)
|
|
|
|
{
|
|
|
|
int err;
|
|
|
|
unsigned long flags;
|
|
|
|
|
|
|
|
err = strict_strtoul(buf, 10, &flags);
|
|
|
|
if (err || flags > UINT_MAX)
|
|
|
|
return -EINVAL;
|
|
|
|
if (flags > KSM_RUN_UNMERGE)
|
|
|
|
return -EINVAL;
|
|
|
|
|
|
|
|
/*
|
|
|
|
* KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
|
|
|
|
* KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
|
2009-12-15 01:59:34 +00:00
|
|
|
* breaking COW to free the pages_shared (but leaves mm_slots
|
|
|
|
* on the list for when ksmd may be set running again).
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
*/
|
|
|
|
|
|
|
|
mutex_lock(&ksm_thread_mutex);
|
|
|
|
if (ksm_run != flags) {
|
|
|
|
ksm_run = flags;
|
2009-09-22 00:02:16 +00:00
|
|
|
if (flags & KSM_RUN_UNMERGE) {
|
2011-05-25 00:11:40 +00:00
|
|
|
int oom_score_adj;
|
|
|
|
|
|
|
|
oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
|
2009-09-22 00:02:16 +00:00
|
|
|
err = unmerge_and_remove_all_rmap_items();
|
2011-11-01 00:07:18 +00:00
|
|
|
compare_swap_oom_score_adj(OOM_SCORE_ADJ_MAX,
|
|
|
|
oom_score_adj);
|
2009-09-22 00:02:16 +00:00
|
|
|
if (err) {
|
|
|
|
ksm_run = KSM_RUN_STOP;
|
|
|
|
count = err;
|
|
|
|
}
|
|
|
|
}
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
|
|
|
mutex_unlock(&ksm_thread_mutex);
|
|
|
|
|
|
|
|
if (flags & KSM_RUN_MERGE)
|
|
|
|
wake_up_interruptible(&ksm_thread_wait);
|
|
|
|
|
|
|
|
return count;
|
|
|
|
}
|
|
|
|
KSM_ATTR(run);
|
|
|
|
|
2009-09-22 00:02:09 +00:00
|
|
|
static ssize_t pages_shared_show(struct kobject *kobj,
|
|
|
|
struct kobj_attribute *attr, char *buf)
|
|
|
|
{
|
|
|
|
return sprintf(buf, "%lu\n", ksm_pages_shared);
|
|
|
|
}
|
|
|
|
KSM_ATTR_RO(pages_shared);
|
|
|
|
|
|
|
|
static ssize_t pages_sharing_show(struct kobject *kobj,
|
|
|
|
struct kobj_attribute *attr, char *buf)
|
|
|
|
{
|
2009-09-22 00:02:10 +00:00
|
|
|
return sprintf(buf, "%lu\n", ksm_pages_sharing);
|
2009-09-22 00:02:09 +00:00
|
|
|
}
|
|
|
|
KSM_ATTR_RO(pages_sharing);
|
|
|
|
|
2009-09-22 00:02:11 +00:00
|
|
|
static ssize_t pages_unshared_show(struct kobject *kobj,
|
|
|
|
struct kobj_attribute *attr, char *buf)
|
|
|
|
{
|
|
|
|
return sprintf(buf, "%lu\n", ksm_pages_unshared);
|
|
|
|
}
|
|
|
|
KSM_ATTR_RO(pages_unshared);
|
|
|
|
|
|
|
|
static ssize_t pages_volatile_show(struct kobject *kobj,
|
|
|
|
struct kobj_attribute *attr, char *buf)
|
|
|
|
{
|
|
|
|
long ksm_pages_volatile;
|
|
|
|
|
|
|
|
ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
|
|
|
|
- ksm_pages_sharing - ksm_pages_unshared;
|
|
|
|
/*
|
|
|
|
* It was not worth any locking to calculate that statistic,
|
|
|
|
* but it might therefore sometimes be negative: conceal that.
|
|
|
|
*/
|
|
|
|
if (ksm_pages_volatile < 0)
|
|
|
|
ksm_pages_volatile = 0;
|
|
|
|
return sprintf(buf, "%ld\n", ksm_pages_volatile);
|
|
|
|
}
|
|
|
|
KSM_ATTR_RO(pages_volatile);
|
|
|
|
|
|
|
|
static ssize_t full_scans_show(struct kobject *kobj,
|
|
|
|
struct kobj_attribute *attr, char *buf)
|
|
|
|
{
|
|
|
|
return sprintf(buf, "%lu\n", ksm_scan.seqnr);
|
|
|
|
}
|
|
|
|
KSM_ATTR_RO(full_scans);
|
|
|
|
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
static struct attribute *ksm_attrs[] = {
|
|
|
|
&sleep_millisecs_attr.attr,
|
|
|
|
&pages_to_scan_attr.attr,
|
|
|
|
&run_attr.attr,
|
2009-09-22 00:02:09 +00:00
|
|
|
&pages_shared_attr.attr,
|
|
|
|
&pages_sharing_attr.attr,
|
2009-09-22 00:02:11 +00:00
|
|
|
&pages_unshared_attr.attr,
|
|
|
|
&pages_volatile_attr.attr,
|
|
|
|
&full_scans_attr.attr,
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
NULL,
|
|
|
|
};
|
|
|
|
|
|
|
|
static struct attribute_group ksm_attr_group = {
|
|
|
|
.attrs = ksm_attrs,
|
|
|
|
.name = "ksm",
|
|
|
|
};
|
2009-09-22 00:02:23 +00:00
|
|
|
#endif /* CONFIG_SYSFS */
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
|
|
|
static int __init ksm_init(void)
|
|
|
|
{
|
|
|
|
struct task_struct *ksm_thread;
|
|
|
|
int err;
|
|
|
|
|
|
|
|
err = ksm_slab_init();
|
|
|
|
if (err)
|
|
|
|
goto out;
|
|
|
|
|
|
|
|
ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
|
|
|
|
if (IS_ERR(ksm_thread)) {
|
|
|
|
printk(KERN_ERR "ksm: creating kthread failed\n");
|
|
|
|
err = PTR_ERR(ksm_thread);
|
2010-08-10 00:20:02 +00:00
|
|
|
goto out_free;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
|
|
|
|
2009-09-22 00:02:23 +00:00
|
|
|
#ifdef CONFIG_SYSFS
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
err = sysfs_create_group(mm_kobj, &ksm_attr_group);
|
|
|
|
if (err) {
|
|
|
|
printk(KERN_ERR "ksm: register sysfs failed\n");
|
2009-09-22 00:02:23 +00:00
|
|
|
kthread_stop(ksm_thread);
|
2010-08-10 00:20:02 +00:00
|
|
|
goto out_free;
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
}
|
2009-10-07 23:32:22 +00:00
|
|
|
#else
|
|
|
|
ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
|
|
|
|
|
2009-09-22 00:02:23 +00:00
|
|
|
#endif /* CONFIG_SYSFS */
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
|
ksm: memory hotremove migration only
The previous patch enables page migration of ksm pages, but that soon gets
into trouble: not surprising, since we're using the ksm page lock to lock
operations on its stable_node, but page migration switches the page whose
lock is to be used for that. Another layer of locking would fix it, but
do we need that yet?
Do we actually need page migration of ksm pages? Yes, memory hotremove
needs to offline sections of memory: and since we stopped allocating ksm
pages with GFP_HIGHUSER, they will tend to be GFP_HIGHUSER_MOVABLE
candidates for migration.
But KSM is currently unconscious of NUMA issues, happily merging pages
from different NUMA nodes: at present the rule must be, not to use
MADV_MERGEABLE where you care about NUMA. So no, NUMA page migration of
ksm pages does not make sense yet.
So, to complete support for ksm swapping we need to make hotremove safe.
ksm_memory_callback() take ksm_thread_mutex when MEM_GOING_OFFLINE and
release it when MEM_OFFLINE or MEM_CANCEL_OFFLINE. But if mapped pages
are freed before migration reaches them, stable_nodes may be left still
pointing to struct pages which have been removed from the system: the
stable_node needs to identify a page by pfn rather than page pointer, then
it can safely prune them when MEM_OFFLINE.
And make NUMA migration skip PageKsm pages where it skips PageReserved.
But it's only when we reach unmap_and_move() that the page lock is taken
and we can be sure that raised pagecount has prevented a PageAnon from
being upgraded: so add offlining arg to migrate_pages(), to migrate ksm
page when offlining (has sufficient locking) but reject it otherwise.
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 01:59:33 +00:00
|
|
|
#ifdef CONFIG_MEMORY_HOTREMOVE
|
|
|
|
/*
|
|
|
|
* Choose a high priority since the callback takes ksm_thread_mutex:
|
|
|
|
* later callbacks could only be taking locks which nest within that.
|
|
|
|
*/
|
|
|
|
hotplug_memory_notifier(ksm_memory_callback, 100);
|
|
|
|
#endif
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
return 0;
|
|
|
|
|
2010-08-10 00:20:02 +00:00
|
|
|
out_free:
|
ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
|
|
|
ksm_slab_free();
|
|
|
|
out:
|
|
|
|
return err;
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2009-09-22 00:01:57 +00:00
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}
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ksm: Kernel SamePage Merging
Ksm is code that allows merging of identical pages between one or more
applications, in a way invisible to the applications that use it. Pages
that are merged are marked as read-only, then COWed when any application
tries to change them.
Whereas fork() allows sharing anonymous pages between parent and child,
ksm can share anonymous pages between unrelated processes.
Ksm works by walking over the memory pages of the applications it scans,
in order to find identical pages. It uses two sorted data structures,
called the stable and unstable trees, to locate identical pages in an
effective way.
When ksm finds two identical pages, it marks them as readonly and merges
them into a single page. After the pages have been marked as readonly and
merged into one, Linux treats them as normal copy-on-write pages, copying
to a fresh anonymous page if write access is required later.
Ksm scans and merges anonymous pages only in those memory areas that have
been registered with it by madvise(addr, length, MADV_MERGEABLE).
The ksm scanner is controlled by sysfs files in /sys/kernel/mm/ksm/:
max_kernel_pages - the maximum number of unswappable kernel pages
which may be allocated by ksm (0 for unlimited).
kernel_pages_allocated - how many ksm pages are currently allocated,
sharing identical content between different
processes (pages unswappable in this release).
pages_shared - how many pages have been saved by sharing with ksm pages
(kernel_pages_allocated being excluded from this count).
pages_to_scan - how many pages ksm should scan before sleeping.
sleep_millisecs - how many milliseconds ksm should sleep between scans.
run - write 0 to disable ksm, read 0 while ksm is disabled (default),
write 1 to run ksm, read 1 while ksm is running,
write 2 to disable ksm and unmerge all its pages.
Includes contributions by Andrea Arcangeli Chris Wright and Hugh Dickins.
[hugh.dickins@tiscali.co.uk: fix rare page leak]
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-09-22 00:02:03 +00:00
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module_init(ksm_init)
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