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Michal Hocko 0ee931c4e3 mm: treewide: remove GFP_TEMPORARY allocation flag 
GFP_TEMPORARY was introduced by commit e12ba74d8f ("Group short-lived
and reclaimable kernel allocations") along with __GFP_RECLAIMABLE.  It's
primary motivation was to allow users to tell that an allocation is
short lived and so the allocator can try to place such allocations close
together and prevent long term fragmentation.  As much as this sounds
like a reasonable semantic it becomes much less clear when to use the
highlevel GFP_TEMPORARY allocation flag.  How long is temporary? Can the
context holding that memory sleep? Can it take locks? It seems there is
no good answer for those questions.

The current implementation of GFP_TEMPORARY is basically GFP_KERNEL |
__GFP_RECLAIMABLE which in itself is tricky because basically none of
the existing caller provide a way to reclaim the allocated memory.  So
this is rather misleading and hard to evaluate for any benefits.

I have checked some random users and none of them has added the flag
with a specific justification.  I suspect most of them just copied from
other existing users and others just thought it might be a good idea to
use without any measuring.  This suggests that GFP_TEMPORARY just
motivates for cargo cult usage without any reasoning.

I believe that our gfp flags are quite complex already and especially
those with highlevel semantic should be clearly defined to prevent from
confusion and abuse.  Therefore I propose dropping GFP_TEMPORARY and
replace all existing users to simply use GFP_KERNEL.  Please note that
SLAB users with shrinkers will still get __GFP_RECLAIMABLE heuristic and
so they will be placed properly for memory fragmentation prevention.

I can see reasons we might want some gfp flag to reflect shorterm
allocations but I propose starting from a clear semantic definition and
only then add users with proper justification.

This was been brought up before LSF this year by Matthew [1] and it
turned out that GFP_TEMPORARY really doesn't have a clear semantic.  It
seems to be a heuristic without any measured advantage for most (if not
all) its current users.  The follow up discussion has revealed that
opinions on what might be temporary allocation differ a lot between
developers.  So rather than trying to tweak existing users into a
semantic which they haven't expected I propose to simply remove the flag
and start from scratch if we really need a semantic for short term
allocations.

[1] http://lkml.kernel.org/r/20170118054945.GD18349@bombadil.infradead.org

[akpm@linux-foundation.org: fix typo]
[akpm@linux-foundation.org: coding-style fixes]
[sfr@canb.auug.org.au: drm/i915: fix up]
  Link: http://lkml.kernel.org/r/20170816144703.378d4f4d@canb.auug.org.au
Link: http://lkml.kernel.org/r/20170728091904.14627-1-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: Mel Gorman <mgorman@suse.de>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Neil Brown <neilb@suse.de>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-09-13 18:53:16 -07:00
arch mm: treewide: remove GFP_TEMPORARY allocation flag 2017-09-13 18:53:16 -07:00
block block: directly insert blk-mq request from blk_insert_cloned_request() 2017-09-11 16:43:57 -06:00
certs modsign: add markers to endif-statements in certs/Makefile 2017-07-14 11:01:37 +10:00
crypto crypto: af_alg - get_page upon reassignment to TX SGL 2017-08-22 15:03:27 +08:00
Documentation The diff is dominated by the Allwinner A10/A20 SoCs getting converted to 2017-09-13 11:04:14 -07:00
drivers mm: treewide: remove GFP_TEMPORARY allocation flag 2017-09-13 18:53:16 -07:00
firmware firmware/Makefile: force recompilation if makefile changes 2017-05-08 17:15:10 -07:00
fs mm: treewide: remove GFP_TEMPORARY allocation flag 2017-09-13 18:53:16 -07:00
include mm: treewide: remove GFP_TEMPORARY allocation flag 2017-09-13 18:53:16 -07:00
init init/main.c: extract early boot entropy from the passed cmdline 2017-09-08 18:26:50 -07:00
ipc ipc: optimize semget/shmget/msgget for lots of keys 2017-09-08 18:26:51 -07:00
kernel mm: treewide: remove GFP_TEMPORARY allocation flag 2017-09-13 18:53:16 -07:00
lib mm: treewide: remove GFP_TEMPORARY allocation flag 2017-09-13 18:53:16 -07:00
mm mm: treewide: remove GFP_TEMPORARY allocation flag 2017-09-13 18:53:16 -07:00
net The highlights include: 2017-09-12 20:03:53 -07:00
samples media updates for v4.14-rc1 2017-09-07 12:53:14 -07:00
scripts Modules updates for v4.14 2017-09-13 11:28:19 -07:00
security selinux/stable-4.14 PR 20170831 2017-09-12 13:21:00 -07:00
sound The diff is dominated by the Allwinner A10/A20 SoCs getting converted to 2017-09-13 11:04:14 -07:00
tools mm: treewide: remove GFP_TEMPORARY allocation flag 2017-09-13 18:53:16 -07:00
usr ramfs: clarify help text that compression applies to ramfs as well as legacy ramdisk. 2017-07-06 16:24:30 -07:00
virt First batch of KVM changes for 4.14 2017-09-08 15:18:36 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: Add support to generate LLVM assembly files 2017-04-25 08:13:52 +09:00
.mailmap power supply and reset changes for the v4.12 series (part 2) 2017-05-12 12:02:21 -07:00
COPYING
CREDITS selinux/stable-4.14 PR 20170831 2017-09-12 13:21:00 -07:00
Kbuild kbuild: Consolidate header generation from ASM offset information 2017-04-13 05:43:37 +09:00
Kconfig
MAINTAINERS Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-09-13 11:56:16 -07:00
Makefile Merge branch 'docs-next' of git://git.lwn.net/linux 2017-09-03 21:07:29 -07:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

README 

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.