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kernel-ark/mm/vmscan.c
Kirill A. Shutemov 7751b2da6b vmscan: split file huge pages before paging them out 
This is preparation of vmscan for file huge pages.  We cannot write out
huge pages, so we need to split them on the way out.

Link: http://lkml.kernel.org/r/1466021202-61880-22-git-send-email-kirill.shutemov@linux.intel.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-07-26 16:19:19 -07:00

3821 lines
109 KiB
C
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/*
* linux/mm/vmscan.c
*
* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
*
* Swap reorganised 29.12.95, Stephen Tweedie.
* kswapd added: 7.1.96 sct
* Removed kswapd_ctl limits, and swap out as many pages as needed
* to bring the system back to freepages.high: 2.4.97, Rik van Riel.
* Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
* Multiqueue VM started 5.8.00, Rik van Riel.
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/gfp.h>
#include <linux/kernel_stat.h>
#include <linux/swap.h>
#include <linux/pagemap.h>
#include <linux/init.h>
#include <linux/highmem.h>
#include <linux/vmpressure.h>
#include <linux/vmstat.h>
#include <linux/file.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
#include <linux/buffer_head.h> /* for try_to_release_page(),
buffer_heads_over_limit */
#include <linux/mm_inline.h>
#include <linux/backing-dev.h>
#include <linux/rmap.h>
#include <linux/topology.h>
#include <linux/cpu.h>
#include <linux/cpuset.h>
#include <linux/compaction.h>
#include <linux/notifier.h>
#include <linux/rwsem.h>
#include <linux/delay.h>
#include <linux/kthread.h>
#include <linux/freezer.h>
#include <linux/memcontrol.h>
#include <linux/delayacct.h>
#include <linux/sysctl.h>
#include <linux/oom.h>
#include <linux/prefetch.h>
#include <linux/printk.h>
#include <linux/dax.h>
#include <asm/tlbflush.h>
#include <asm/div64.h>
#include <linux/swapops.h>
#include <linux/balloon_compaction.h>
#include "internal.h"
#define CREATE_TRACE_POINTS
#include <trace/events/vmscan.h>
struct scan_control {
/* How many pages shrink_list() should reclaim */
unsigned long nr_to_reclaim;
/* This context's GFP mask */
gfp_t gfp_mask;
/* Allocation order */
int order;
/*
* Nodemask of nodes allowed by the caller. If NULL, all nodes
* are scanned.
*/
nodemask_t *nodemask;
/*
* The memory cgroup that hit its limit and as a result is the
* primary target of this reclaim invocation.
*/
struct mem_cgroup *target_mem_cgroup;
/* Scan (total_size >> priority) pages at once */
int priority;
unsigned int may_writepage:1;
/* Can mapped pages be reclaimed? */
unsigned int may_unmap:1;
/* Can pages be swapped as part of reclaim? */
unsigned int may_swap:1;
/* Can cgroups be reclaimed below their normal consumption range? */
unsigned int may_thrash:1;
unsigned int hibernation_mode:1;
/* One of the zones is ready for compaction */
unsigned int compaction_ready:1;
/* Incremented by the number of inactive pages that were scanned */
unsigned long nr_scanned;
/* Number of pages freed so far during a call to shrink_zones() */
unsigned long nr_reclaimed;
};
#ifdef ARCH_HAS_PREFETCH
#define prefetch_prev_lru_page(_page, _base, _field) \
do { \
if ((_page)->lru.prev != _base) { \
struct page *prev; \
\
prev = lru_to_page(&(_page->lru)); \
prefetch(&prev->_field); \
} \
} while (0)
#else
#define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
#endif
#ifdef ARCH_HAS_PREFETCHW
#define prefetchw_prev_lru_page(_page, _base, _field) \
do { \
if ((_page)->lru.prev != _base) { \
struct page *prev; \
\
prev = lru_to_page(&(_page->lru)); \
prefetchw(&prev->_field); \
} \
} while (0)
#else
#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
#endif
/*
* From 0 .. 100. Higher means more swappy.
*/
int vm_swappiness = 60;
/*
* The total number of pages which are beyond the high watermark within all
* zones.
*/
unsigned long vm_total_pages;
static LIST_HEAD(shrinker_list);
static DECLARE_RWSEM(shrinker_rwsem);
#ifdef CONFIG_MEMCG
static bool global_reclaim(struct scan_control *sc)
{
return !sc->target_mem_cgroup;
}
/**
* sane_reclaim - is the usual dirty throttling mechanism operational?
* @sc: scan_control in question
*
* The normal page dirty throttling mechanism in balance_dirty_pages() is
* completely broken with the legacy memcg and direct stalling in
* shrink_page_list() is used for throttling instead, which lacks all the
* niceties such as fairness, adaptive pausing, bandwidth proportional
* allocation and configurability.
*
* This function tests whether the vmscan currently in progress can assume
* that the normal dirty throttling mechanism is operational.
*/
static bool sane_reclaim(struct scan_control *sc)
{
struct mem_cgroup *memcg = sc->target_mem_cgroup;
if (!memcg)
return true;
#ifdef CONFIG_CGROUP_WRITEBACK
if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
return true;
#endif
return false;
}
#else
static bool global_reclaim(struct scan_control *sc)
{
return true;
}
static bool sane_reclaim(struct scan_control *sc)
{
return true;
}
#endif
unsigned long zone_reclaimable_pages(struct zone *zone)
{
unsigned long nr;
nr = zone_page_state_snapshot(zone, NR_ACTIVE_FILE) +
zone_page_state_snapshot(zone, NR_INACTIVE_FILE) +
zone_page_state_snapshot(zone, NR_ISOLATED_FILE);
if (get_nr_swap_pages() > 0)
nr += zone_page_state_snapshot(zone, NR_ACTIVE_ANON) +
zone_page_state_snapshot(zone, NR_INACTIVE_ANON) +
zone_page_state_snapshot(zone, NR_ISOLATED_ANON);
return nr;
}
bool zone_reclaimable(struct zone *zone)
{
return zone_page_state_snapshot(zone, NR_PAGES_SCANNED) <
zone_reclaimable_pages(zone) * 6;
}
unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru)
{
if (!mem_cgroup_disabled())
return mem_cgroup_get_lru_size(lruvec, lru);
return zone_page_state(lruvec_zone(lruvec), NR_LRU_BASE + lru);
}
/*
* Add a shrinker callback to be called from the vm.
*/
int register_shrinker(struct shrinker *shrinker)
{
size_t size = sizeof(*shrinker->nr_deferred);
if (shrinker->flags & SHRINKER_NUMA_AWARE)
size *= nr_node_ids;
shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
if (!shrinker->nr_deferred)
return -ENOMEM;
down_write(&shrinker_rwsem);
list_add_tail(&shrinker->list, &shrinker_list);
up_write(&shrinker_rwsem);
return 0;
}
EXPORT_SYMBOL(register_shrinker);
/*
* Remove one
*/
void unregister_shrinker(struct shrinker *shrinker)
{
down_write(&shrinker_rwsem);
list_del(&shrinker->list);
up_write(&shrinker_rwsem);
kfree(shrinker->nr_deferred);
}
EXPORT_SYMBOL(unregister_shrinker);
#define SHRINK_BATCH 128
static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
struct shrinker *shrinker,
unsigned long nr_scanned,
unsigned long nr_eligible)
{
unsigned long freed = 0;
unsigned long long delta;
long total_scan;
long freeable;
long nr;
long new_nr;
int nid = shrinkctl->nid;
long batch_size = shrinker->batch ? shrinker->batch
: SHRINK_BATCH;
freeable = shrinker->count_objects(shrinker, shrinkctl);
if (freeable == 0)
return 0;
/*
* copy the current shrinker scan count into a local variable
* and zero it so that other concurrent shrinker invocations
* don't also do this scanning work.
*/
nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
total_scan = nr;
delta = (4 * nr_scanned) / shrinker->seeks;
delta *= freeable;
do_div(delta, nr_eligible + 1);
total_scan += delta;
if (total_scan < 0) {
pr_err("shrink_slab: %pF negative objects to delete nr=%ld\n",
shrinker->scan_objects, total_scan);
total_scan = freeable;
}
/*
* We need to avoid excessive windup on filesystem shrinkers
* due to large numbers of GFP_NOFS allocations causing the
* shrinkers to return -1 all the time. This results in a large
* nr being built up so when a shrink that can do some work
* comes along it empties the entire cache due to nr >>>
* freeable. This is bad for sustaining a working set in
* memory.
*
* Hence only allow the shrinker to scan the entire cache when
* a large delta change is calculated directly.
*/
if (delta < freeable / 4)
total_scan = min(total_scan, freeable / 2);
/*
* Avoid risking looping forever due to too large nr value:
* never try to free more than twice the estimate number of
* freeable entries.
*/
if (total_scan > freeable * 2)
total_scan = freeable * 2;
trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
nr_scanned, nr_eligible,
freeable, delta, total_scan);
/*
* Normally, we should not scan less than batch_size objects in one
* pass to avoid too frequent shrinker calls, but if the slab has less
* than batch_size objects in total and we are really tight on memory,
* we will try to reclaim all available objects, otherwise we can end
* up failing allocations although there are plenty of reclaimable
* objects spread over several slabs with usage less than the
* batch_size.
*
* We detect the "tight on memory" situations by looking at the total
* number of objects we want to scan (total_scan). If it is greater
* than the total number of objects on slab (freeable), we must be
* scanning at high prio and therefore should try to reclaim as much as
* possible.
*/
while (total_scan >= batch_size ||
total_scan >= freeable) {
unsigned long ret;
unsigned long nr_to_scan = min(batch_size, total_scan);
shrinkctl->nr_to_scan = nr_to_scan;
ret = shrinker->scan_objects(shrinker, shrinkctl);
if (ret == SHRINK_STOP)
break;
freed += ret;
count_vm_events(SLABS_SCANNED, nr_to_scan);
total_scan -= nr_to_scan;
cond_resched();
}
/*
* move the unused scan count back into the shrinker in a
* manner that handles concurrent updates. If we exhausted the
* scan, there is no need to do an update.
*/
if (total_scan > 0)
new_nr = atomic_long_add_return(total_scan,
&shrinker->nr_deferred[nid]);
else
new_nr = atomic_long_read(&shrinker->nr_deferred[nid]);
trace_mm_shrink_slab_end(shrinker, nid, freed, nr, new_nr, total_scan);
return freed;
}
/**
* shrink_slab - shrink slab caches
* @gfp_mask: allocation context
* @nid: node whose slab caches to target
* @memcg: memory cgroup whose slab caches to target
* @nr_scanned: pressure numerator
* @nr_eligible: pressure denominator
*
* Call the shrink functions to age shrinkable caches.
*
* @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set,
* unaware shrinkers will receive a node id of 0 instead.
*
* @memcg specifies the memory cgroup to target. If it is not NULL,
* only shrinkers with SHRINKER_MEMCG_AWARE set will be called to scan
* objects from the memory cgroup specified. Otherwise, only unaware
* shrinkers are called.
*
* @nr_scanned and @nr_eligible form a ratio that indicate how much of
* the available objects should be scanned. Page reclaim for example
* passes the number of pages scanned and the number of pages on the
* LRU lists that it considered on @nid, plus a bias in @nr_scanned
* when it encountered mapped pages. The ratio is further biased by
* the ->seeks setting of the shrink function, which indicates the
* cost to recreate an object relative to that of an LRU page.
*
* Returns the number of reclaimed slab objects.
*/
static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
struct mem_cgroup *memcg,
unsigned long nr_scanned,
unsigned long nr_eligible)
{
struct shrinker *shrinker;
unsigned long freed = 0;
if (memcg && (!memcg_kmem_enabled() || !mem_cgroup_online(memcg)))
return 0;
if (nr_scanned == 0)
nr_scanned = SWAP_CLUSTER_MAX;
if (!down_read_trylock(&shrinker_rwsem)) {
/*
* If we would return 0, our callers would understand that we
* have nothing else to shrink and give up trying. By returning
* 1 we keep it going and assume we'll be able to shrink next
* time.
*/
freed = 1;
goto out;
}
list_for_each_entry(shrinker, &shrinker_list, list) {
struct shrink_control sc = {
.gfp_mask = gfp_mask,
.nid = nid,
.memcg = memcg,
};
/*
* If kernel memory accounting is disabled, we ignore
* SHRINKER_MEMCG_AWARE flag and call all shrinkers
* passing NULL for memcg.
*/
if (memcg_kmem_enabled() &&
!!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE))
continue;
if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
sc.nid = 0;
freed += do_shrink_slab(&sc, shrinker, nr_scanned, nr_eligible);
}
up_read(&shrinker_rwsem);
out:
cond_resched();
return freed;
}
void drop_slab_node(int nid)
{
unsigned long freed;
do {
struct mem_cgroup *memcg = NULL;
freed = 0;
do {
freed += shrink_slab(GFP_KERNEL, nid, memcg,
1000, 1000);
} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
} while (freed > 10);
}
void drop_slab(void)
{
int nid;
for_each_online_node(nid)
drop_slab_node(nid);
}
static inline int is_page_cache_freeable(struct page *page)
{
/*
* A freeable page cache page is referenced only by the caller
* that isolated the page, the page cache radix tree and
* optional buffer heads at page->private.
*/
return page_count(page) - page_has_private(page) == 2;
}
static int may_write_to_inode(struct inode *inode, struct scan_control *sc)
{
if (current->flags & PF_SWAPWRITE)
return 1;
if (!inode_write_congested(inode))
return 1;
if (inode_to_bdi(inode) == current->backing_dev_info)
return 1;
return 0;
}
/*
* We detected a synchronous write error writing a page out. Probably
* -ENOSPC. We need to propagate that into the address_space for a subsequent
* fsync(), msync() or close().
*
* The tricky part is that after writepage we cannot touch the mapping: nothing
* prevents it from being freed up. But we have a ref on the page and once
* that page is locked, the mapping is pinned.
*
* We're allowed to run sleeping lock_page() here because we know the caller has
* __GFP_FS.
*/
static void handle_write_error(struct address_space *mapping,
struct page *page, int error)
{
lock_page(page);
if (page_mapping(page) == mapping)
mapping_set_error(mapping, error);
unlock_page(page);
}
/* possible outcome of pageout() */
typedef enum {
/* failed to write page out, page is locked */
PAGE_KEEP,
/* move page to the active list, page is locked */
PAGE_ACTIVATE,
/* page has been sent to the disk successfully, page is unlocked */
PAGE_SUCCESS,
/* page is clean and locked */
PAGE_CLEAN,
} pageout_t;
/*
* pageout is called by shrink_page_list() for each dirty page.
* Calls ->writepage().
*/
static pageout_t pageout(struct page *page, struct address_space *mapping,
struct scan_control *sc)
{
/*
* If the page is dirty, only perform writeback if that write
* will be non-blocking. To prevent this allocation from being
* stalled by pagecache activity. But note that there may be
* stalls if we need to run get_block(). We could test
* PagePrivate for that.
*
* If this process is currently in __generic_file_write_iter() against
* this page's queue, we can perform writeback even if that
* will block.
*
* If the page is swapcache, write it back even if that would
* block, for some throttling. This happens by accident, because
* swap_backing_dev_info is bust: it doesn't reflect the
* congestion state of the swapdevs. Easy to fix, if needed.
*/
if (!is_page_cache_freeable(page))
return PAGE_KEEP;
if (!mapping) {
/*
* Some data journaling orphaned pages can have
* page->mapping == NULL while being dirty with clean buffers.
*/
if (page_has_private(page)) {
if (try_to_free_buffers(page)) {
ClearPageDirty(page);
pr_info("%s: orphaned page\n", __func__);
return PAGE_CLEAN;
}
}
return PAGE_KEEP;
}
if (mapping->a_ops->writepage == NULL)
return PAGE_ACTIVATE;
if (!may_write_to_inode(mapping->host, sc))
return PAGE_KEEP;
if (clear_page_dirty_for_io(page)) {
int res;
struct writeback_control wbc = {
.sync_mode = WB_SYNC_NONE,
.nr_to_write = SWAP_CLUSTER_MAX,
.range_start = 0,
.range_end = LLONG_MAX,
.for_reclaim = 1,
};
SetPageReclaim(page);
res = mapping->a_ops->writepage(page, &wbc);
if (res < 0)
handle_write_error(mapping, page, res);
if (res == AOP_WRITEPAGE_ACTIVATE) {
ClearPageReclaim(page);
return PAGE_ACTIVATE;
}
if (!PageWriteback(page)) {
/* synchronous write or broken a_ops? */
ClearPageReclaim(page);
}
trace_mm_vmscan_writepage(page);
inc_zone_page_state(page, NR_VMSCAN_WRITE);
return PAGE_SUCCESS;
}
return PAGE_CLEAN;
}
/*
* Same as remove_mapping, but if the page is removed from the mapping, it
* gets returned with a refcount of 0.
*/
static int __remove_mapping(struct address_space *mapping, struct page *page,
bool reclaimed)
{
unsigned long flags;
BUG_ON(!PageLocked(page));
BUG_ON(mapping != page_mapping(page));
spin_lock_irqsave(&mapping->tree_lock, flags);
/*
* The non racy check for a busy page.
*
* Must be careful with the order of the tests. When someone has
* a ref to the page, it may be possible that they dirty it then
* drop the reference. So if PageDirty is tested before page_count
* here, then the following race may occur:
*
* get_user_pages(&page);
* [user mapping goes away]
* write_to(page);
* !PageDirty(page) [good]
* SetPageDirty(page);
* put_page(page);
* !page_count(page) [good, discard it]
*
* [oops, our write_to data is lost]
*
* Reversing the order of the tests ensures such a situation cannot
* escape unnoticed. The smp_rmb is needed to ensure the page->flags
* load is not satisfied before that of page->_refcount.
*
* Note that if SetPageDirty is always performed via set_page_dirty,
* and thus under tree_lock, then this ordering is not required.
*/
if (!page_ref_freeze(page, 2))
goto cannot_free;
/* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
if (unlikely(PageDirty(page))) {
page_ref_unfreeze(page, 2);
goto cannot_free;
}
if (PageSwapCache(page)) {
swp_entry_t swap = { .val = page_private(page) };
mem_cgroup_swapout(page, swap);
__delete_from_swap_cache(page);
spin_unlock_irqrestore(&mapping->tree_lock, flags);
swapcache_free(swap);
} else {
void (*freepage)(struct page *);
void *shadow = NULL;
freepage = mapping->a_ops->freepage;
/*
* Remember a shadow entry for reclaimed file cache in
* order to detect refaults, thus thrashing, later on.
*
* But don't store shadows in an address space that is
* already exiting. This is not just an optizimation,
* inode reclaim needs to empty out the radix tree or
* the nodes are lost. Don't plant shadows behind its
* back.
*
* We also don't store shadows for DAX mappings because the
* only page cache pages found in these are zero pages
* covering holes, and because we don't want to mix DAX
* exceptional entries and shadow exceptional entries in the
* same page_tree.
*/
if (reclaimed && page_is_file_cache(page) &&
!mapping_exiting(mapping) && !dax_mapping(mapping))
shadow = workingset_eviction(mapping, page);
__delete_from_page_cache(page, shadow);
spin_unlock_irqrestore(&mapping->tree_lock, flags);
if (freepage != NULL)
freepage(page);
}
return 1;
cannot_free:
spin_unlock_irqrestore(&mapping->tree_lock, flags);
return 0;
}
/*
* Attempt to detach a locked page from its ->mapping. If it is dirty or if
* someone else has a ref on the page, abort and return 0. If it was
* successfully detached, return 1. Assumes the caller has a single ref on
* this page.
*/
int remove_mapping(struct address_space *mapping, struct page *page)
{
if (__remove_mapping(mapping, page, false)) {
/*
* Unfreezing the refcount with 1 rather than 2 effectively
* drops the pagecache ref for us without requiring another
* atomic operation.
*/
page_ref_unfreeze(page, 1);
return 1;
}
return 0;
}
/**
* putback_lru_page - put previously isolated page onto appropriate LRU list
* @page: page to be put back to appropriate lru list
*
* Add previously isolated @page to appropriate LRU list.
* Page may still be unevictable for other reasons.
*
* lru_lock must not be held, interrupts must be enabled.
*/
void putback_lru_page(struct page *page)
{
bool is_unevictable;
int was_unevictable = PageUnevictable(page);
VM_BUG_ON_PAGE(PageLRU(page), page);
redo:
ClearPageUnevictable(page);
if (page_evictable(page)) {
/*
* For evictable pages, we can use the cache.
* In event of a race, worst case is we end up with an
* unevictable page on [in]active list.
* We know how to handle that.
*/
is_unevictable = false;
lru_cache_add(page);
} else {
/*
* Put unevictable pages directly on zone's unevictable
* list.
*/
is_unevictable = true;
add_page_to_unevictable_list(page);
/*
* When racing with an mlock or AS_UNEVICTABLE clearing
* (page is unlocked) make sure that if the other thread
* does not observe our setting of PG_lru and fails
* isolation/check_move_unevictable_pages,
* we see PG_mlocked/AS_UNEVICTABLE cleared below and move
* the page back to the evictable list.
*
* The other side is TestClearPageMlocked() or shmem_lock().
*/
smp_mb();
}
/*
* page's status can change while we move it among lru. If an evictable
* page is on unevictable list, it never be freed. To avoid that,
* check after we added it to the list, again.
*/
if (is_unevictable && page_evictable(page)) {
if (!isolate_lru_page(page)) {
put_page(page);
goto redo;
}
/* This means someone else dropped this page from LRU
* So, it will be freed or putback to LRU again. There is
* nothing to do here.
*/
}
if (was_unevictable && !is_unevictable)
count_vm_event(UNEVICTABLE_PGRESCUED);
else if (!was_unevictable && is_unevictable)
count_vm_event(UNEVICTABLE_PGCULLED);
put_page(page); /* drop ref from isolate */
}
enum page_references {
PAGEREF_RECLAIM,
PAGEREF_RECLAIM_CLEAN,
PAGEREF_KEEP,
PAGEREF_ACTIVATE,
};
static enum page_references page_check_references(struct page *page,
struct scan_control *sc)
{
int referenced_ptes, referenced_page;
unsigned long vm_flags;
referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
&vm_flags);
referenced_page = TestClearPageReferenced(page);
/*
* Mlock lost the isolation race with us. Let try_to_unmap()
* move the page to the unevictable list.
*/
if (vm_flags & VM_LOCKED)
return PAGEREF_RECLAIM;
if (referenced_ptes) {
if (PageSwapBacked(page))
return PAGEREF_ACTIVATE;
/*
* All mapped pages start out with page table
* references from the instantiating fault, so we need
* to look twice if a mapped file page is used more
* than once.
*
* Mark it and spare it for another trip around the
* inactive list. Another page table reference will
* lead to its activation.
*
* Note: the mark is set for activated pages as well
* so that recently deactivated but used pages are
* quickly recovered.
*/
SetPageReferenced(page);
if (referenced_page || referenced_ptes > 1)
return PAGEREF_ACTIVATE;
/*
* Activate file-backed executable pages after first usage.
*/
if (vm_flags & VM_EXEC)
return PAGEREF_ACTIVATE;
return PAGEREF_KEEP;
}
/* Reclaim if clean, defer dirty pages to writeback */
if (referenced_page && !PageSwapBacked(page))
return PAGEREF_RECLAIM_CLEAN;
return PAGEREF_RECLAIM;
}
/* Check if a page is dirty or under writeback */
static void page_check_dirty_writeback(struct page *page,
bool *dirty, bool *writeback)
{
struct address_space *mapping;
/*
* Anonymous pages are not handled by flushers and must be written
* from reclaim context. Do not stall reclaim based on them
*/
if (!page_is_file_cache(page)) {
*dirty = false;
*writeback = false;
return;
}
/* By default assume that the page flags are accurate */
*dirty = PageDirty(page);
*writeback = PageWriteback(page);
/* Verify dirty/writeback state if the filesystem supports it */
if (!page_has_private(page))
return;
mapping = page_mapping(page);
if (mapping && mapping->a_ops->is_dirty_writeback)
mapping->a_ops->is_dirty_writeback(page, dirty, writeback);
}
/*
* shrink_page_list() returns the number of reclaimed pages
*/
static unsigned long shrink_page_list(struct list_head *page_list,
struct zone *zone,
struct scan_control *sc,
enum ttu_flags ttu_flags,
unsigned long *ret_nr_dirty,
unsigned long *ret_nr_unqueued_dirty,
unsigned long *ret_nr_congested,
unsigned long *ret_nr_writeback,
unsigned long *ret_nr_immediate,
bool force_reclaim)
{
LIST_HEAD(ret_pages);
LIST_HEAD(free_pages);
int pgactivate = 0;
unsigned long nr_unqueued_dirty = 0;
unsigned long nr_dirty = 0;
unsigned long nr_congested = 0;
unsigned long nr_reclaimed = 0;
unsigned long nr_writeback = 0;
unsigned long nr_immediate = 0;
cond_resched();
while (!list_empty(page_list)) {
struct address_space *mapping;
struct page *page;
int may_enter_fs;
enum page_references references = PAGEREF_RECLAIM_CLEAN;
bool dirty, writeback;
bool lazyfree = false;
int ret = SWAP_SUCCESS;
cond_resched();
page = lru_to_page(page_list);
list_del(&page->lru);
if (!trylock_page(page))
goto keep;
VM_BUG_ON_PAGE(PageActive(page), page);
VM_BUG_ON_PAGE(page_zone(page) != zone, page);
sc->nr_scanned++;
if (unlikely(!page_evictable(page)))
goto cull_mlocked;
if (!sc->may_unmap && page_mapped(page))
goto keep_locked;
/* Double the slab pressure for mapped and swapcache pages */
if (page_mapped(page) || PageSwapCache(page))
sc->nr_scanned++;
may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
/*
* The number of dirty pages determines if a zone is marked
* reclaim_congested which affects wait_iff_congested. kswapd
* will stall and start writing pages if the tail of the LRU
* is all dirty unqueued pages.
*/
page_check_dirty_writeback(page, &dirty, &writeback);
if (dirty || writeback)
nr_dirty++;
if (dirty && !writeback)
nr_unqueued_dirty++;
/*
* Treat this page as congested if the underlying BDI is or if
* pages are cycling through the LRU so quickly that the
* pages marked for immediate reclaim are making it to the
* end of the LRU a second time.
*/
mapping = page_mapping(page);
if (((dirty || writeback) && mapping &&
inode_write_congested(mapping->host)) ||
(writeback && PageReclaim(page)))
nr_congested++;
/*
* If a page at the tail of the LRU is under writeback, there
* are three cases to consider.
*
* 1) If reclaim is encountering an excessive number of pages
* under writeback and this page is both under writeback and
* PageReclaim then it indicates that pages are being queued
* for IO but are being recycled through the LRU before the
* IO can complete. Waiting on the page itself risks an
* indefinite stall if it is impossible to writeback the
* page due to IO error or disconnected storage so instead
* note that the LRU is being scanned too quickly and the
* caller can stall after page list has been processed.
*
* 2) Global or new memcg reclaim encounters a page that is
* not marked for immediate reclaim, or the caller does not
* have __GFP_FS (or __GFP_IO if it's simply going to swap,
* not to fs). In this case mark the page for immediate
* reclaim and continue scanning.
*
* Require may_enter_fs because we would wait on fs, which
* may not have submitted IO yet. And the loop driver might
* enter reclaim, and deadlock if it waits on a page for
* which it is needed to do the write (loop masks off
* __GFP_IO|__GFP_FS for this reason); but more thought
* would probably show more reasons.
*
* 3) Legacy memcg encounters a page that is already marked
* PageReclaim. memcg does not have any dirty pages
* throttling so we could easily OOM just because too many
* pages are in writeback and there is nothing else to
* reclaim. Wait for the writeback to complete.
*/
if (PageWriteback(page)) {
/* Case 1 above */
if (current_is_kswapd() &&
PageReclaim(page) &&
test_bit(ZONE_WRITEBACK, &zone->flags)) {
nr_immediate++;
goto keep_locked;
/* Case 2 above */
} else if (sane_reclaim(sc) ||
!PageReclaim(page) || !may_enter_fs) {
/*
* This is slightly racy - end_page_writeback()
* might have just cleared PageReclaim, then
* setting PageReclaim here end up interpreted
* as PageReadahead - but that does not matter
* enough to care. What we do want is for this
* page to have PageReclaim set next time memcg
* reclaim reaches the tests above, so it will
* then wait_on_page_writeback() to avoid OOM;
* and it's also appropriate in global reclaim.
*/
SetPageReclaim(page);
nr_writeback++;
goto keep_locked;
/* Case 3 above */
} else {
unlock_page(page);
wait_on_page_writeback(page);
/* then go back and try same page again */
list_add_tail(&page->lru, page_list);
continue;
}
}
if (!force_reclaim)
references = page_check_references(page, sc);
switch (references) {
case PAGEREF_ACTIVATE:
goto activate_locked;
case PAGEREF_KEEP:
goto keep_locked;
case PAGEREF_RECLAIM:
case PAGEREF_RECLAIM_CLEAN:
; /* try to reclaim the page below */
}
/*
* Anonymous process memory has backing store?
* Try to allocate it some swap space here.
*/
if (PageAnon(page) && !PageSwapCache(page)) {
if (!(sc->gfp_mask & __GFP_IO))
goto keep_locked;
if (!add_to_swap(page, page_list))
goto activate_locked;
lazyfree = true;
may_enter_fs = 1;
/* Adding to swap updated mapping */
mapping = page_mapping(page);
} else if (unlikely(PageTransHuge(page))) {
/* Split file THP */
if (split_huge_page_to_list(page, page_list))
goto keep_locked;
}
VM_BUG_ON_PAGE(PageTransHuge(page), page);
/*
* The page is mapped into the page tables of one or more
* processes. Try to unmap it here.
*/
if (page_mapped(page) && mapping) {
switch (ret = try_to_unmap(page, lazyfree ?
(ttu_flags | TTU_BATCH_FLUSH | TTU_LZFREE) :
(ttu_flags | TTU_BATCH_FLUSH))) {
case SWAP_FAIL:
goto activate_locked;
case SWAP_AGAIN:
goto keep_locked;
case SWAP_MLOCK:
goto cull_mlocked;
case SWAP_LZFREE:
goto lazyfree;
case SWAP_SUCCESS:
; /* try to free the page below */
}
}
if (PageDirty(page)) {
/*
* Only kswapd can writeback filesystem pages to
* avoid risk of stack overflow but only writeback
* if many dirty pages have been encountered.
*/
if (page_is_file_cache(page) &&
(!current_is_kswapd() ||
!test_bit(ZONE_DIRTY, &zone->flags))) {
/*
* Immediately reclaim when written back.
* Similar in principal to deactivate_page()
* except we already have the page isolated
* and know it's dirty
*/
inc_zone_page_state(page, NR_VMSCAN_IMMEDIATE);
SetPageReclaim(page);
goto keep_locked;
}
if (references == PAGEREF_RECLAIM_CLEAN)
goto keep_locked;
if (!may_enter_fs)
goto keep_locked;
if (!sc->may_writepage)
goto keep_locked;
/*
* Page is dirty. Flush the TLB if a writable entry
* potentially exists to avoid CPU writes after IO
* starts and then write it out here.
*/
try_to_unmap_flush_dirty();
switch (pageout(page, mapping, sc)) {
case PAGE_KEEP:
goto keep_locked;
case PAGE_ACTIVATE:
goto activate_locked;
case PAGE_SUCCESS:
if (PageWriteback(page))
goto keep;
if (PageDirty(page))
goto keep;
/*
* A synchronous write - probably a ramdisk. Go
* ahead and try to reclaim the page.
*/
if (!trylock_page(page))
goto keep;
if (PageDirty(page) || PageWriteback(page))
goto keep_locked;
mapping = page_mapping(page);
case PAGE_CLEAN:
; /* try to free the page below */
}
}
/*
* If the page has buffers, try to free the buffer mappings
* associated with this page. If we succeed we try to free
* the page as well.
*
* We do this even if the page is PageDirty().
* try_to_release_page() does not perform I/O, but it is
* possible for a page to have PageDirty set, but it is actually
* clean (all its buffers are clean). This happens if the
* buffers were written out directly, with submit_bh(). ext3
* will do this, as well as the blockdev mapping.
* try_to_release_page() will discover that cleanness and will
* drop the buffers and mark the page clean - it can be freed.
*
* Rarely, pages can have buffers and no ->mapping. These are
* the pages which were not successfully invalidated in
* truncate_complete_page(). We try to drop those buffers here
* and if that worked, and the page is no longer mapped into
* process address space (page_count == 1) it can be freed.
* Otherwise, leave the page on the LRU so it is swappable.
*/
if (page_has_private(page)) {
if (!try_to_release_page(page, sc->gfp_mask))
goto activate_locked;
if (!mapping && page_count(page) == 1) {
unlock_page(page);
if (put_page_testzero(page))
goto free_it;
else {
/*
* rare race with speculative reference.
* the speculative reference will free
* this page shortly, so we may
* increment nr_reclaimed here (and
* leave it off the LRU).
*/
nr_reclaimed++;
continue;
}
}
}
lazyfree:
if (!mapping || !__remove_mapping(mapping, page, true))
goto keep_locked;
/*
* At this point, we have no other references and there is
* no way to pick any more up (removed from LRU, removed
* from pagecache). Can use non-atomic bitops now (and
* we obviously don't have to worry about waking up a process
* waiting on the page lock, because there are no references.
*/
__ClearPageLocked(page);
free_it:
if (ret == SWAP_LZFREE)
count_vm_event(PGLAZYFREED);
nr_reclaimed++;
/*
* Is there need to periodically free_page_list? It would
* appear not as the counts should be low
*/
list_add(&page->lru, &free_pages);
continue;
cull_mlocked:
if (PageSwapCache(page))
try_to_free_swap(page);
unlock_page(page);
list_add(&page->lru, &ret_pages);
continue;
activate_locked:
/* Not a candidate for swapping, so reclaim swap space. */
if (PageSwapCache(page) && mem_cgroup_swap_full(page))
try_to_free_swap(page);
VM_BUG_ON_PAGE(PageActive(page), page);
SetPageActive(page);
pgactivate++;
keep_locked:
unlock_page(page);
keep:
list_add(&page->lru, &ret_pages);
VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page);
}
mem_cgroup_uncharge_list(&free_pages);
try_to_unmap_flush();
free_hot_cold_page_list(&free_pages, true);
list_splice(&ret_pages, page_list);
count_vm_events(PGACTIVATE, pgactivate);
*ret_nr_dirty += nr_dirty;
*ret_nr_congested += nr_congested;
*ret_nr_unqueued_dirty += nr_unqueued_dirty;
*ret_nr_writeback += nr_writeback;
*ret_nr_immediate += nr_immediate;
return nr_reclaimed;
}
unsigned long reclaim_clean_pages_from_list(struct zone *zone,
struct list_head *page_list)
{
struct scan_control sc = {
.gfp_mask = GFP_KERNEL,
.priority = DEF_PRIORITY,
.may_unmap = 1,
};
unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5;
struct page *page, *next;
LIST_HEAD(clean_pages);
list_for_each_entry_safe(page, next, page_list, lru) {
if (page_is_file_cache(page) && !PageDirty(page) &&
!__PageMovable(page)) {
ClearPageActive(page);
list_move(&page->lru, &clean_pages);
}
}
ret = shrink_page_list(&clean_pages, zone, &sc,
TTU_UNMAP|TTU_IGNORE_ACCESS,
&dummy1, &dummy2, &dummy3, &dummy4, &dummy5, true);
list_splice(&clean_pages, page_list);
mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret);
return ret;
}
/*
* Attempt to remove the specified page from its LRU. Only take this page
* if it is of the appropriate PageActive status. Pages which are being
* freed elsewhere are also ignored.
*
* page: page to consider
* mode: one of the LRU isolation modes defined above
*
* returns 0 on success, -ve errno on failure.
*/
int __isolate_lru_page(struct page *page, isolate_mode_t mode)
{
int ret = -EINVAL;
/* Only take pages on the LRU. */
if (!PageLRU(page))
return ret;
/* Compaction should not handle unevictable pages but CMA can do so */
if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
return ret;
ret = -EBUSY;
/*
* To minimise LRU disruption, the caller can indicate that it only
* wants to isolate pages it will be able to operate on without
* blocking - clean pages for the most part.
*
* ISOLATE_CLEAN means that only clean pages should be isolated. This
* is used by reclaim when it is cannot write to backing storage
*
* ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
* that it is possible to migrate without blocking
*/
if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) {
/* All the caller can do on PageWriteback is block */
if (PageWriteback(page))
return ret;
if (PageDirty(page)) {
struct address_space *mapping;
/* ISOLATE_CLEAN means only clean pages */
if (mode & ISOLATE_CLEAN)
return ret;
/*
* Only pages without mappings or that have a
* ->migratepage callback are possible to migrate
* without blocking
*/
mapping = page_mapping(page);
if (mapping && !mapping->a_ops->migratepage)
return ret;
}
}
if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
return ret;
if (likely(get_page_unless_zero(page))) {
/*
* Be careful not to clear PageLRU until after we're
* sure the page is not being freed elsewhere -- the
* page release code relies on it.
*/
ClearPageLRU(page);
ret = 0;
}
return ret;
}
/*
* zone->lru_lock is heavily contended. Some of the functions that
* shrink the lists perform better by taking out a batch of pages
* and working on them outside the LRU lock.
*
* For pagecache intensive workloads, this function is the hottest
* spot in the kernel (apart from copy_*_user functions).
*
* Appropriate locks must be held before calling this function.
*
* @nr_to_scan: The number of pages to look through on the list.
* @lruvec: The LRU vector to pull pages from.
* @dst: The temp list to put pages on to.
* @nr_scanned: The number of pages that were scanned.
* @sc: The scan_control struct for this reclaim session
* @mode: One of the LRU isolation modes
* @lru: LRU list id for isolating
*
* returns how many pages were moved onto *@dst.
*/
static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
struct lruvec *lruvec, struct list_head *dst,
unsigned long *nr_scanned, struct scan_control *sc,
isolate_mode_t mode, enum lru_list lru)
{
struct list_head *src = &lruvec->lists[lru];
unsigned long nr_taken = 0;
unsigned long scan;
for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan &&
!list_empty(src); scan++) {
struct page *page;
page = lru_to_page(src);
prefetchw_prev_lru_page(page, src, flags);
VM_BUG_ON_PAGE(!PageLRU(page), page);
switch (__isolate_lru_page(page, mode)) {
case 0:
nr_taken += hpage_nr_pages(page);
list_move(&page->lru, dst);
break;
case -EBUSY:
/* else it is being freed elsewhere */
list_move(&page->lru, src);
continue;
default:
BUG();
}
}
*nr_scanned = scan;
trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
nr_taken, mode, is_file_lru(lru));
return nr_taken;
}
/**
* isolate_lru_page - tries to isolate a page from its LRU list
* @page: page to isolate from its LRU list
*
* Isolates a @page from an LRU list, clears PageLRU and adjusts the
* vmstat statistic corresponding to whatever LRU list the page was on.
*
* Returns 0 if the page was removed from an LRU list.
* Returns -EBUSY if the page was not on an LRU list.
*
* The returned page will have PageLRU() cleared. If it was found on
* the active list, it will have PageActive set. If it was found on
* the unevictable list, it will have the PageUnevictable bit set. That flag
* may need to be cleared by the caller before letting the page go.
*
* The vmstat statistic corresponding to the list on which the page was
* found will be decremented.
*
* Restrictions:
* (1) Must be called with an elevated refcount on the page. This is a
* fundamentnal difference from isolate_lru_pages (which is called
* without a stable reference).
* (2) the lru_lock must not be held.
* (3) interrupts must be enabled.
*/
int isolate_lru_page(struct page *page)
{
int ret = -EBUSY;
VM_BUG_ON_PAGE(!page_count(page), page);
WARN_RATELIMIT(PageTail(page), "trying to isolate tail page");
if (PageLRU(page)) {
struct zone *zone = page_zone(page);
struct lruvec *lruvec;
spin_lock_irq(&zone->lru_lock);
lruvec = mem_cgroup_page_lruvec(page, zone);
if (PageLRU(page)) {
int lru = page_lru(page);
get_page(page);
ClearPageLRU(page);
del_page_from_lru_list(page, lruvec, lru);
ret = 0;
}
spin_unlock_irq(&zone->lru_lock);
}
return ret;
}
/*
* A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
* then get resheduled. When there are massive number of tasks doing page
* allocation, such sleeping direct reclaimers may keep piling up on each CPU,
* the LRU list will go small and be scanned faster than necessary, leading to
* unnecessary swapping, thrashing and OOM.
*/
static int too_many_isolated(struct zone *zone, int file,
struct scan_control *sc)
{
unsigned long inactive, isolated;
if (current_is_kswapd())
return 0;
if (!sane_reclaim(sc))
return 0;
if (file) {
inactive = zone_page_state(zone, NR_INACTIVE_FILE);
isolated = zone_page_state(zone, NR_ISOLATED_FILE);
} else {
inactive = zone_page_state(zone, NR_INACTIVE_ANON);
isolated = zone_page_state(zone, NR_ISOLATED_ANON);
}
/*
* GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they
* won't get blocked by normal direct-reclaimers, forming a circular
* deadlock.
*/
if ((sc->gfp_mask & (__GFP_IO | __GFP_FS)) == (__GFP_IO | __GFP_FS))
inactive >>= 3;
return isolated > inactive;
}
static noinline_for_stack void
putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
{
struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
struct zone *zone = lruvec_zone(lruvec);
LIST_HEAD(pages_to_free);
/*
* Put back any unfreeable pages.
*/
while (!list_empty(page_list)) {
struct page *page = lru_to_page(page_list);
int lru;
VM_BUG_ON_PAGE(PageLRU(page), page);
list_del(&page->lru);
if (unlikely(!page_evictable(page))) {
spin_unlock_irq(&zone->lru_lock);
putback_lru_page(page);
spin_lock_irq(&zone->lru_lock);
continue;
}
lruvec = mem_cgroup_page_lruvec(page, zone);
SetPageLRU(page);
lru = page_lru(page);
add_page_to_lru_list(page, lruvec, lru);
if (is_active_lru(lru)) {
int file = is_file_lru(lru);
int numpages = hpage_nr_pages(page);
reclaim_stat->recent_rotated[file] += numpages;
}
if (put_page_testzero(page)) {
__ClearPageLRU(page);
__ClearPageActive(page);
del_page_from_lru_list(page, lruvec, lru);
if (unlikely(PageCompound(page))) {
spin_unlock_irq(&zone->lru_lock);
mem_cgroup_uncharge(page);
(*get_compound_page_dtor(page))(page);
spin_lock_irq(&zone->lru_lock);
} else
list_add(&page->lru, &pages_to_free);
}
}
/*
* To save our caller's stack, now use input list for pages to free.
*/
list_splice(&pages_to_free, page_list);
}
/*
* If a kernel thread (such as nfsd for loop-back mounts) services
* a backing device by writing to the page cache it sets PF_LESS_THROTTLE.
* In that case we should only throttle if the backing device it is
* writing to is congested. In other cases it is safe to throttle.
*/
static int current_may_throttle(void)
{
return !(current->flags & PF_LESS_THROTTLE) ||
current->backing_dev_info == NULL ||
bdi_write_congested(current->backing_dev_info);
}
/*
* shrink_inactive_list() is a helper for shrink_zone(). It returns the number
* of reclaimed pages
*/
static noinline_for_stack unsigned long
shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
struct scan_control *sc, enum lru_list lru)
{
LIST_HEAD(page_list);
unsigned long nr_scanned;
unsigned long nr_reclaimed = 0;
unsigned long nr_taken;
unsigned long nr_dirty = 0;
unsigned long nr_congested = 0;
unsigned long nr_unqueued_dirty = 0;
unsigned long nr_writeback = 0;
unsigned long nr_immediate = 0;
isolate_mode_t isolate_mode = 0;
int file = is_file_lru(lru);
struct zone *zone = lruvec_zone(lruvec);
struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
while (unlikely(too_many_isolated(zone, file, sc))) {
congestion_wait(BLK_RW_ASYNC, HZ/10);
/* We are about to die and free our memory. Return now. */
if (fatal_signal_pending(current))
return SWAP_CLUSTER_MAX;
}
lru_add_drain();
if (!sc->may_unmap)
isolate_mode |= ISOLATE_UNMAPPED;
if (!sc->may_writepage)
isolate_mode |= ISOLATE_CLEAN;
spin_lock_irq(&zone->lru_lock);
nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
&nr_scanned, sc, isolate_mode, lru);
update_lru_size(lruvec, lru, -nr_taken);
__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
reclaim_stat->recent_scanned[file] += nr_taken;
if (global_reclaim(sc)) {
__mod_zone_page_state(zone, NR_PAGES_SCANNED, nr_scanned);
if (current_is_kswapd())
__count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scanned);
else
__count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scanned);
}
spin_unlock_irq(&zone->lru_lock);
if (nr_taken == 0)
return 0;
nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
&nr_dirty, &nr_unqueued_dirty, &nr_congested,
&nr_writeback, &nr_immediate,
false);
spin_lock_irq(&zone->lru_lock);
if (global_reclaim(sc)) {
if (current_is_kswapd())
__count_zone_vm_events(PGSTEAL_KSWAPD, zone,
nr_reclaimed);
else
__count_zone_vm_events(PGSTEAL_DIRECT, zone,
nr_reclaimed);
}
putback_inactive_pages(lruvec, &page_list);
__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
spin_unlock_irq(&zone->lru_lock);
mem_cgroup_uncharge_list(&page_list);
free_hot_cold_page_list(&page_list, true);
/*
* If reclaim is isolating dirty pages under writeback, it implies
* that the long-lived page allocation rate is exceeding the page
* laundering rate. Either the global limits are not being effective
* at throttling processes due to the page distribution throughout
* zones or there is heavy usage of a slow backing device. The
* only option is to throttle from reclaim context which is not ideal
* as there is no guarantee the dirtying process is throttled in the
* same way balance_dirty_pages() manages.
*
* Once a zone is flagged ZONE_WRITEBACK, kswapd will count the number
* of pages under pages flagged for immediate reclaim and stall if any
* are encountered in the nr_immediate check below.
*/
if (nr_writeback && nr_writeback == nr_taken)
set_bit(ZONE_WRITEBACK, &zone->flags);
/*
* Legacy memcg will stall in page writeback so avoid forcibly
* stalling here.
*/
if (sane_reclaim(sc)) {
/*
* Tag a zone as congested if all the dirty pages scanned were
* backed by a congested BDI and wait_iff_congested will stall.
*/
if (nr_dirty && nr_dirty == nr_congested)
set_bit(ZONE_CONGESTED, &zone->flags);
/*
* If dirty pages are scanned that are not queued for IO, it
* implies that flushers are not keeping up. In this case, flag
* the zone ZONE_DIRTY and kswapd will start writing pages from
* reclaim context.
*/
if (nr_unqueued_dirty == nr_taken)
set_bit(ZONE_DIRTY, &zone->flags);
/*
* If kswapd scans pages marked marked for immediate
* reclaim and under writeback (nr_immediate), it implies
* that pages are cycling through the LRU faster than
* they are written so also forcibly stall.
*/
if (nr_immediate && current_may_throttle())
congestion_wait(BLK_RW_ASYNC, HZ/10);
}
/*
* Stall direct reclaim for IO completions if underlying BDIs or zone
* is congested. Allow kswapd to continue until it starts encountering
* unqueued dirty pages or cycling through the LRU too quickly.
*/
if (!sc->hibernation_mode && !current_is_kswapd() &&
current_may_throttle())
wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
trace_mm_vmscan_lru_shrink_inactive(zone, nr_scanned, nr_reclaimed,
sc->priority, file);
return nr_reclaimed;
}
/*
* This moves pages from the active list to the inactive list.
*
* We move them the other way if the page is referenced by one or more
* processes, from rmap.
*
* If the pages are mostly unmapped, the processing is fast and it is
* appropriate to hold zone->lru_lock across the whole operation. But if
* the pages are mapped, the processing is slow (page_referenced()) so we
* should drop zone->lru_lock around each page. It's impossible to balance
* this, so instead we remove the pages from the LRU while processing them.
* It is safe to rely on PG_active against the non-LRU pages in here because
* nobody will play with that bit on a non-LRU page.
*
* The downside is that we have to touch page->_refcount against each page.
* But we had to alter page->flags anyway.
*/
static void move_active_pages_to_lru(struct lruvec *lruvec,
struct list_head *list,
struct list_head *pages_to_free,
enum lru_list lru)
{
struct zone *zone = lruvec_zone(lruvec);
unsigned long pgmoved = 0;
struct page *page;
int nr_pages;
while (!list_empty(list)) {
page = lru_to_page(list);
lruvec = mem_cgroup_page_lruvec(page, zone);
VM_BUG_ON_PAGE(PageLRU(page), page);
SetPageLRU(page);
nr_pages = hpage_nr_pages(page);
update_lru_size(lruvec, lru, nr_pages);
list_move(&page->lru, &lruvec->lists[lru]);
pgmoved += nr_pages;
if (put_page_testzero(page)) {
__ClearPageLRU(page);
__ClearPageActive(page);
del_page_from_lru_list(page, lruvec, lru);
if (unlikely(PageCompound(page))) {
spin_unlock_irq(&zone->lru_lock);
mem_cgroup_uncharge(page);
(*get_compound_page_dtor(page))(page);
spin_lock_irq(&zone->lru_lock);
} else
list_add(&page->lru, pages_to_free);
}
}
if (!is_active_lru(lru))
__count_vm_events(PGDEACTIVATE, pgmoved);
}
static void shrink_active_list(unsigned long nr_to_scan,
struct lruvec *lruvec,
struct scan_control *sc,
enum lru_list lru)
{
unsigned long nr_taken;
unsigned long nr_scanned;
unsigned long vm_flags;
LIST_HEAD(l_hold); /* The pages which were snipped off */
LIST_HEAD(l_active);
LIST_HEAD(l_inactive);
struct page *page;
struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
unsigned long nr_rotated = 0;
isolate_mode_t isolate_mode = 0;
int file = is_file_lru(lru);
struct zone *zone = lruvec_zone(lruvec);
lru_add_drain();
if (!sc->may_unmap)
isolate_mode |= ISOLATE_UNMAPPED;
if (!sc->may_writepage)
isolate_mode |= ISOLATE_CLEAN;
spin_lock_irq(&zone->lru_lock);
nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
&nr_scanned, sc, isolate_mode, lru);
update_lru_size(lruvec, lru, -nr_taken);
__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
reclaim_stat->recent_scanned[file] += nr_taken;
if (global_reclaim(sc))
__mod_zone_page_state(zone, NR_PAGES_SCANNED, nr_scanned);
__count_zone_vm_events(PGREFILL, zone, nr_scanned);
spin_unlock_irq(&zone->lru_lock);
while (!list_empty(&l_hold)) {
cond_resched();
page = lru_to_page(&l_hold);
list_del(&page->lru);
if (unlikely(!page_evictable(page))) {
putback_lru_page(page);
continue;
}
if (unlikely(buffer_heads_over_limit)) {
if (page_has_private(page) && trylock_page(page)) {
if (page_has_private(page))
try_to_release_page(page, 0);
unlock_page(page);
}
}
if (page_referenced(page, 0, sc->target_mem_cgroup,
&vm_flags)) {
nr_rotated += hpage_nr_pages(page);
/*
* Identify referenced, file-backed active pages and
* give them one more trip around the active list. So
* that executable code get better chances to stay in
* memory under moderate memory pressure. Anon pages
* are not likely to be evicted by use-once streaming
* IO, plus JVM can create lots of anon VM_EXEC pages,
* so we ignore them here.
*/
if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
list_add(&page->lru, &l_active);
continue;
}
}
ClearPageActive(page); /* we are de-activating */
list_add(&page->lru, &l_inactive);
}
/*
* Move pages back to the lru list.
*/
spin_lock_irq(&zone->lru_lock);
/*
* Count referenced pages from currently used mappings as rotated,
* even though only some of them are actually re-activated. This
* helps balance scan pressure between file and anonymous pages in
* get_scan_count.
*/
reclaim_stat->recent_rotated[file] += nr_rotated;
move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
spin_unlock_irq(&zone->lru_lock);
mem_cgroup_uncharge_list(&l_hold);
free_hot_cold_page_list(&l_hold, true);
}
/*
* The inactive anon list should be small enough that the VM never has
* to do too much work.
*
* The inactive file list should be small enough to leave most memory
* to the established workingset on the scan-resistant active list,
* but large enough to avoid thrashing the aggregate readahead window.
*
* Both inactive lists should also be large enough that each inactive
* page has a chance to be referenced again before it is reclaimed.
*
* The inactive_ratio is the target ratio of ACTIVE to INACTIVE pages
* on this LRU, maintained by the pageout code. A zone->inactive_ratio
* of 3 means 3:1 or 25% of the pages are kept on the inactive list.
*
* total target max
* memory ratio inactive
* -------------------------------------
* 10MB 1 5MB
* 100MB 1 50MB
* 1GB 3 250MB
* 10GB 10 0.9GB
* 100GB 31 3GB
* 1TB 101 10GB
* 10TB 320 32GB
*/
static bool inactive_list_is_low(struct lruvec *lruvec, bool file)
{
unsigned long inactive_ratio;
unsigned long inactive;
unsigned long active;
unsigned long gb;
/*
* If we don't have swap space, anonymous page deactivation
* is pointless.
*/
if (!file && !total_swap_pages)
return false;
inactive = lruvec_lru_size(lruvec, file * LRU_FILE);
active = lruvec_lru_size(lruvec, file * LRU_FILE + LRU_ACTIVE);
gb = (inactive + active) >> (30 - PAGE_SHIFT);
if (gb)
inactive_ratio = int_sqrt(10 * gb);
else
inactive_ratio = 1;
return inactive * inactive_ratio < active;
}
static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
struct lruvec *lruvec, struct scan_control *sc)
{
if (is_active_lru(lru)) {
if (inactive_list_is_low(lruvec, is_file_lru(lru)))
shrink_active_list(nr_to_scan, lruvec, sc, lru);
return 0;
}
return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
}
enum scan_balance {
SCAN_EQUAL,
SCAN_FRACT,
SCAN_ANON,
SCAN_FILE,
};
/*
* Determine how aggressively the anon and file LRU lists should be
* scanned. The relative value of each set of LRU lists is determined
* by looking at the fraction of the pages scanned we did rotate back
* onto the active list instead of evict.
*
* nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
* nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
*/
static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
struct scan_control *sc, unsigned long *nr,
unsigned long *lru_pages)
{
int swappiness = mem_cgroup_swappiness(memcg);
struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
u64 fraction[2];
u64 denominator = 0; /* gcc */
struct zone *zone = lruvec_zone(lruvec);
unsigned long anon_prio, file_prio;
enum scan_balance scan_balance;
unsigned long anon, file;
bool force_scan = false;
unsigned long ap, fp;
enum lru_list lru;
bool some_scanned;
int pass;
/*
* If the zone or memcg is small, nr[l] can be 0. This
* results in no scanning on this priority and a potential
* priority drop. Global direct reclaim can go to the next
* zone and tends to have no problems. Global kswapd is for
* zone balancing and it needs to scan a minimum amount. When
* reclaiming for a memcg, a priority drop can cause high
* latencies, so it's better to scan a minimum amount there as
* well.
*/
if (current_is_kswapd()) {
if (!zone_reclaimable(zone))
force_scan = true;
if (!mem_cgroup_online(memcg))
force_scan = true;
}
if (!global_reclaim(sc))
force_scan = true;
/* If we have no swap space, do not bother scanning anon pages. */
if (!sc->may_swap || mem_cgroup_get_nr_swap_pages(memcg) <= 0) {
scan_balance = SCAN_FILE;
goto out;
}
/*
* Global reclaim will swap to prevent OOM even with no
* swappiness, but memcg users want to use this knob to
* disable swapping for individual groups completely when
* using the memory controller's swap limit feature would be
* too expensive.
*/
if (!global_reclaim(sc) && !swappiness) {
scan_balance = SCAN_FILE;
goto out;
}
/*
* Do not apply any pressure balancing cleverness when the
* system is close to OOM, scan both anon and file equally
* (unless the swappiness setting disagrees with swapping).
*/
if (!sc->priority && swappiness) {
scan_balance = SCAN_EQUAL;
goto out;
}
/*
* Prevent the reclaimer from falling into the cache trap: as
* cache pages start out inactive, every cache fault will tip
* the scan balance towards the file LRU. And as the file LRU
* shrinks, so does the window for rotation from references.
* This means we have a runaway feedback loop where a tiny
* thrashing file LRU becomes infinitely more attractive than
* anon pages. Try to detect this based on file LRU size.
*/
if (global_reclaim(sc)) {
unsigned long zonefile;
unsigned long zonefree;
zonefree = zone_page_state(zone, NR_FREE_PAGES);
zonefile = zone_page_state(zone, NR_ACTIVE_FILE) +
zone_page_state(zone, NR_INACTIVE_FILE);
if (unlikely(zonefile + zonefree <= high_wmark_pages(zone))) {
scan_balance = SCAN_ANON;
goto out;
}
}
/*
* If there is enough inactive page cache, i.e. if the size of the
* inactive list is greater than that of the active list *and* the
* inactive list actually has some pages to scan on this priority, we
* do not reclaim anything from the anonymous working set right now.
* Without the second condition we could end up never scanning an
* lruvec even if it has plenty of old anonymous pages unless the
* system is under heavy pressure.
*/
if (!inactive_list_is_low(lruvec, true) &&
lruvec_lru_size(lruvec, LRU_INACTIVE_FILE) >> sc->priority) {
scan_balance = SCAN_FILE;
goto out;
}
scan_balance = SCAN_FRACT;
/*
* With swappiness at 100, anonymous and file have the same priority.
* This scanning priority is essentially the inverse of IO cost.
*/
anon_prio = swappiness;
file_prio = 200 - anon_prio;
/*
* OK, so we have swap space and a fair amount of page cache
* pages. We use the recently rotated / recently scanned
* ratios to determine how valuable each cache is.
*
* Because workloads change over time (and to avoid overflow)
* we keep these statistics as a floating average, which ends
* up weighing recent references more than old ones.
*
* anon in [0], file in [1]
*/
anon = lruvec_lru_size(lruvec, LRU_ACTIVE_ANON) +
lruvec_lru_size(lruvec, LRU_INACTIVE_ANON);
file = lruvec_lru_size(lruvec, LRU_ACTIVE_FILE) +
lruvec_lru_size(lruvec, LRU_INACTIVE_FILE);
spin_lock_irq(&zone->lru_lock);
if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
reclaim_stat->recent_scanned[0] /= 2;
reclaim_stat->recent_rotated[0] /= 2;
}
if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
reclaim_stat->recent_scanned[1] /= 2;
reclaim_stat->recent_rotated[1] /= 2;
}
/*
* The amount of pressure on anon vs file pages is inversely
* proportional to the fraction of recently scanned pages on
* each list that were recently referenced and in active use.
*/
ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
ap /= reclaim_stat->recent_rotated[0] + 1;
fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
fp /= reclaim_stat->recent_rotated[1] + 1;
spin_unlock_irq(&zone->lru_lock);
fraction[0] = ap;
fraction[1] = fp;
denominator = ap + fp + 1;
out:
some_scanned = false;
/* Only use force_scan on second pass. */
for (pass = 0; !some_scanned && pass < 2; pass++) {
*lru_pages = 0;
for_each_evictable_lru(lru) {
int file = is_file_lru(lru);
unsigned long size;
unsigned long scan;
size = lruvec_lru_size(lruvec, lru);
scan = size >> sc->priority;
if (!scan && pass && force_scan)
scan = min(size, SWAP_CLUSTER_MAX);
switch (scan_balance) {
case SCAN_EQUAL:
/* Scan lists relative to size */
break;
case SCAN_FRACT:
/*
* Scan types proportional to swappiness and
* their relative recent reclaim efficiency.
*/
scan = div64_u64(scan * fraction[file],
denominator);
break;
case SCAN_FILE:
case SCAN_ANON:
/* Scan one type exclusively */
if ((scan_balance == SCAN_FILE) != file) {
size = 0;
scan = 0;
}
break;
default:
/* Look ma, no brain */
BUG();
}
*lru_pages += size;
nr[lru] = scan;
/*
* Skip the second pass and don't force_scan,
* if we found something to scan.
*/
some_scanned |= !!scan;
}
}
}
#ifdef CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
static void init_tlb_ubc(void)
{
/*
* This deliberately does not clear the cpumask as it's expensive
* and unnecessary. If there happens to be data in there then the
* first SWAP_CLUSTER_MAX pages will send an unnecessary IPI and
* then will be cleared.
*/
current->tlb_ubc.flush_required = false;
}
#else
static inline void init_tlb_ubc(void)
{
}
#endif /* CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH */
/*
* This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
*/
static void shrink_zone_memcg(struct zone *zone, struct mem_cgroup *memcg,
struct scan_control *sc, unsigned long *lru_pages)
{
struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
unsigned long nr[NR_LRU_LISTS];
unsigned long targets[NR_LRU_LISTS];
unsigned long nr_to_scan;
enum lru_list lru;
unsigned long nr_reclaimed = 0;
unsigned long nr_to_reclaim = sc->nr_to_reclaim;
struct blk_plug plug;
bool scan_adjusted;
get_scan_count(lruvec, memcg, sc, nr, lru_pages);
/* Record the original scan target for proportional adjustments later */
memcpy(targets, nr, sizeof(nr));
/*
* Global reclaiming within direct reclaim at DEF_PRIORITY is a normal
* event that can occur when there is little memory pressure e.g.
* multiple streaming readers/writers. Hence, we do not abort scanning
* when the requested number of pages are reclaimed when scanning at
* DEF_PRIORITY on the assumption that the fact we are direct
* reclaiming implies that kswapd is not keeping up and it is best to
* do a batch of work at once. For memcg reclaim one check is made to
* abort proportional reclaim if either the file or anon lru has already
* dropped to zero at the first pass.
*/
scan_adjusted = (global_reclaim(sc) && !current_is_kswapd() &&
sc->priority == DEF_PRIORITY);
init_tlb_ubc();
blk_start_plug(&plug);
while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
nr[LRU_INACTIVE_FILE]) {
unsigned long nr_anon, nr_file, percentage;
unsigned long nr_scanned;
for_each_evictable_lru(lru) {
if (nr[lru]) {
nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
nr[lru] -= nr_to_scan;
nr_reclaimed += shrink_list(lru, nr_to_scan,
lruvec, sc);
}
}
if (nr_reclaimed < nr_to_reclaim || scan_adjusted)
continue;
/*
* For kswapd and memcg, reclaim at least the number of pages
* requested. Ensure that the anon and file LRUs are scanned
* proportionally what was requested by get_scan_count(). We
* stop reclaiming one LRU and reduce the amount scanning
* proportional to the original scan target.
*/
nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE];
nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON];
/*
* It's just vindictive to attack the larger once the smaller
* has gone to zero. And given the way we stop scanning the
* smaller below, this makes sure that we only make one nudge
* towards proportionality once we've got nr_to_reclaim.
*/
if (!nr_file || !nr_anon)
break;
if (nr_file > nr_anon) {
unsigned long scan_target = targets[LRU_INACTIVE_ANON] +
targets[LRU_ACTIVE_ANON] + 1;
lru = LRU_BASE;
percentage = nr_anon * 100 / scan_target;
} else {
unsigned long scan_target = targets[LRU_INACTIVE_FILE] +
targets[LRU_ACTIVE_FILE] + 1;
lru = LRU_FILE;
percentage = nr_file * 100 / scan_target;
}
/* Stop scanning the smaller of the LRU */
nr[lru] = 0;
nr[lru + LRU_ACTIVE] = 0;
/*
* Recalculate the other LRU scan count based on its original
* scan target and the percentage scanning already complete
*/
lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
nr_scanned = targets[lru] - nr[lru];
nr[lru] = targets[lru] * (100 - percentage) / 100;
nr[lru] -= min(nr[lru], nr_scanned);
lru += LRU_ACTIVE;
nr_scanned = targets[lru] - nr[lru];
nr[lru] = targets[lru] * (100 - percentage) / 100;
nr[lru] -= min(nr[lru], nr_scanned);
scan_adjusted = true;
}
blk_finish_plug(&plug);
sc->nr_reclaimed += nr_reclaimed;
/*
* Even if we did not try to evict anon pages at all, we want to
* rebalance the anon lru active/inactive ratio.
*/
if (inactive_list_is_low(lruvec, false))
shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
sc, LRU_ACTIVE_ANON);
throttle_vm_writeout(sc->gfp_mask);
}
/* Use reclaim/compaction for costly allocs or under memory pressure */
static bool in_reclaim_compaction(struct scan_control *sc)
{
if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
(sc->order > PAGE_ALLOC_COSTLY_ORDER ||
sc->priority < DEF_PRIORITY - 2))
return true;
return false;
}
/*
* Reclaim/compaction is used for high-order allocation requests. It reclaims
* order-0 pages before compacting the zone. should_continue_reclaim() returns
* true if more pages should be reclaimed such that when the page allocator
* calls try_to_compact_zone() that it will have enough free pages to succeed.
* It will give up earlier than that if there is difficulty reclaiming pages.
*/
static inline bool should_continue_reclaim(struct zone *zone,
unsigned long nr_reclaimed,
unsigned long nr_scanned,
struct scan_control *sc)
{
unsigned long pages_for_compaction;
unsigned long inactive_lru_pages;
/* If not in reclaim/compaction mode, stop */
if (!in_reclaim_compaction(sc))
return false;
/* Consider stopping depending on scan and reclaim activity */
if (sc->gfp_mask & __GFP_REPEAT) {
/*
* For __GFP_REPEAT allocations, stop reclaiming if the
* full LRU list has been scanned and we are still failing
* to reclaim pages. This full LRU scan is potentially
* expensive but a __GFP_REPEAT caller really wants to succeed
*/
if (!nr_reclaimed && !nr_scanned)
return false;
} else {
/*
* For non-__GFP_REPEAT allocations which can presumably
* fail without consequence, stop if we failed to reclaim
* any pages from the last SWAP_CLUSTER_MAX number of
* pages that were scanned. This will return to the
* caller faster at the risk reclaim/compaction and
* the resulting allocation attempt fails
*/
if (!nr_reclaimed)
return false;
}
/*
* If we have not reclaimed enough pages for compaction and the
* inactive lists are large enough, continue reclaiming
*/
pages_for_compaction = (2UL << sc->order);
inactive_lru_pages = zone_page_state(zone, NR_INACTIVE_FILE);
if (get_nr_swap_pages() > 0)
inactive_lru_pages += zone_page_state(zone, NR_INACTIVE_ANON);
if (sc->nr_reclaimed < pages_for_compaction &&
inactive_lru_pages > pages_for_compaction)
return true;
/* If compaction would go ahead or the allocation would succeed, stop */
switch (compaction_suitable(zone, sc->order, 0, 0)) {
case COMPACT_PARTIAL:
case COMPACT_CONTINUE:
return false;
default:
return true;
}
}
static bool shrink_zone(struct zone *zone, struct scan_control *sc,
bool is_classzone)
{
struct reclaim_state *reclaim_state = current->reclaim_state;
unsigned long nr_reclaimed, nr_scanned;
bool reclaimable = false;
do {
struct mem_cgroup *root = sc->target_mem_cgroup;
struct mem_cgroup_reclaim_cookie reclaim = {
.zone = zone,
.priority = sc->priority,
};
unsigned long zone_lru_pages = 0;
struct mem_cgroup *memcg;
nr_reclaimed = sc->nr_reclaimed;
nr_scanned = sc->nr_scanned;
memcg = mem_cgroup_iter(root, NULL, &reclaim);
do {
unsigned long lru_pages;
unsigned long reclaimed;
unsigned long scanned;
if (mem_cgroup_low(root, memcg)) {
if (!sc->may_thrash)
continue;
mem_cgroup_events(memcg, MEMCG_LOW, 1);
}
reclaimed = sc->nr_reclaimed;
scanned = sc->nr_scanned;
shrink_zone_memcg(zone, memcg, sc, &lru_pages);
zone_lru_pages += lru_pages;
if (memcg && is_classzone)
shrink_slab(sc->gfp_mask, zone_to_nid(zone),
memcg, sc->nr_scanned - scanned,
lru_pages);
/* Record the group's reclaim efficiency */
vmpressure(sc->gfp_mask, memcg, false,
sc->nr_scanned - scanned,
sc->nr_reclaimed - reclaimed);
/*
* Direct reclaim and kswapd have to scan all memory
* cgroups to fulfill the overall scan target for the
* zone.
*
* Limit reclaim, on the other hand, only cares about
* nr_to_reclaim pages to be reclaimed and it will
* retry with decreasing priority if one round over the
* whole hierarchy is not sufficient.
*/
if (!global_reclaim(sc) &&
sc->nr_reclaimed >= sc->nr_to_reclaim) {
mem_cgroup_iter_break(root, memcg);
break;
}
} while ((memcg = mem_cgroup_iter(root, memcg, &reclaim)));
/*
* Shrink the slab caches in the same proportion that
* the eligible LRU pages were scanned.
*/
if (global_reclaim(sc) && is_classzone)
shrink_slab(sc->gfp_mask, zone_to_nid(zone), NULL,
sc->nr_scanned - nr_scanned,
zone_lru_pages);
if (reclaim_state) {
sc->nr_reclaimed += reclaim_state->reclaimed_slab;
reclaim_state->reclaimed_slab = 0;
}
/* Record the subtree's reclaim efficiency */
vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true,
sc->nr_scanned - nr_scanned,
sc->nr_reclaimed - nr_reclaimed);
if (sc->nr_reclaimed - nr_reclaimed)
reclaimable = true;
} while (should_continue_reclaim(zone, sc->nr_reclaimed - nr_reclaimed,
sc->nr_scanned - nr_scanned, sc));
return reclaimable;
}
/*
* Returns true if compaction should go ahead for a high-order request, or
* the high-order allocation would succeed without compaction.
*/
static inline bool compaction_ready(struct zone *zone, int order, int classzone_idx)
{
unsigned long balance_gap, watermark;
bool watermark_ok;
/*
* Compaction takes time to run and there are potentially other
* callers using the pages just freed. Continue reclaiming until
* there is a buffer of free pages available to give compaction
* a reasonable chance of completing and allocating the page
*/
balance_gap = min(low_wmark_pages(zone), DIV_ROUND_UP(
zone->managed_pages, KSWAPD_ZONE_BALANCE_GAP_RATIO));
watermark = high_wmark_pages(zone) + balance_gap + (2UL << order);
watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, classzone_idx);
/*
* If compaction is deferred, reclaim up to a point where
* compaction will have a chance of success when re-enabled
*/
if (compaction_deferred(zone, order))
return watermark_ok;
/*
* If compaction is not ready to start and allocation is not likely
* to succeed without it, then keep reclaiming.
*/
if (compaction_suitable(zone, order, 0, classzone_idx) == COMPACT_SKIPPED)
return false;
return watermark_ok;
}
/*
* This is the direct reclaim path, for page-allocating processes. We only
* try to reclaim pages from zones which will satisfy the caller's allocation
* request.
*
* We reclaim from a zone even if that zone is over high_wmark_pages(zone).
* Because:
* a) The caller may be trying to free *extra* pages to satisfy a higher-order
* allocation or
* b) The target zone may be at high_wmark_pages(zone) but the lower zones
* must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
* zone defense algorithm.
*
* If a zone is deemed to be full of pinned pages then just give it a light
* scan then give up on it.
*/
static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
{
struct zoneref *z;
struct zone *zone;
unsigned long nr_soft_reclaimed;
unsigned long nr_soft_scanned;
gfp_t orig_mask;
enum zone_type requested_highidx = gfp_zone(sc->gfp_mask);
/*
* If the number of buffer_heads in the machine exceeds the maximum
* allowed level, force direct reclaim to scan the highmem zone as
* highmem pages could be pinning lowmem pages storing buffer_heads
*/
orig_mask = sc->gfp_mask;
if (buffer_heads_over_limit)
sc->gfp_mask |= __GFP_HIGHMEM;
for_each_zone_zonelist_nodemask(zone, z, zonelist,
gfp_zone(sc->gfp_mask), sc->nodemask) {
enum zone_type classzone_idx;
if (!populated_zone(zone))
continue;
classzone_idx = requested_highidx;
while (!populated_zone(zone->zone_pgdat->node_zones +
classzone_idx))
classzone_idx--;
/*
* Take care memory controller reclaiming has small influence
* to global LRU.
*/
if (global_reclaim(sc)) {
if (!cpuset_zone_allowed(zone,
GFP_KERNEL | __GFP_HARDWALL))
continue;
if (sc->priority != DEF_PRIORITY &&
!zone_reclaimable(zone))
continue; /* Let kswapd poll it */
/*
* If we already have plenty of memory free for
* compaction in this zone, don't free any more.
* Even though compaction is invoked for any
* non-zero order, only frequent costly order
* reclamation is disruptive enough to become a
* noticeable problem, like transparent huge
* page allocations.
*/
if (IS_ENABLED(CONFIG_COMPACTION) &&
sc->order > PAGE_ALLOC_COSTLY_ORDER &&
zonelist_zone_idx(z) <= requested_highidx &&
compaction_ready(zone, sc->order, requested_highidx)) {
sc->compaction_ready = true;
continue;
}
/*
* This steals pages from memory cgroups over softlimit
* and returns the number of reclaimed pages and
* scanned pages. This works for global memory pressure
* and balancing, not for a memcg's limit.
*/
nr_soft_scanned = 0;
nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
sc->order, sc->gfp_mask,
&nr_soft_scanned);
sc->nr_reclaimed += nr_soft_reclaimed;
sc->nr_scanned += nr_soft_scanned;
/* need some check for avoid more shrink_zone() */
}
shrink_zone(zone, sc, zone_idx(zone) == classzone_idx);
}
/*
* Restore to original mask to avoid the impact on the caller if we
* promoted it to __GFP_HIGHMEM.
*/
sc->gfp_mask = orig_mask;
}
/*
* This is the main entry point to direct page reclaim.
*
* If a full scan of the inactive list fails to free enough memory then we
* are "out of memory" and something needs to be killed.
*
* If the caller is !__GFP_FS then the probability of a failure is reasonably
* high - the zone may be full of dirty or under-writeback pages, which this
* caller can't do much about. We kick the writeback threads and take explicit
* naps in the hope that some of these pages can be written. But if the
* allocating task holds filesystem locks which prevent writeout this might not
* work, and the allocation attempt will fail.
*
* returns: 0, if no pages reclaimed
* else, the number of pages reclaimed
*/
static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
struct scan_control *sc)
{
int initial_priority = sc->priority;
unsigned long total_scanned = 0;
unsigned long writeback_threshold;
retry:
delayacct_freepages_start();
if (global_reclaim(sc))
count_vm_event(ALLOCSTALL);
do {
vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
sc->priority);
sc->nr_scanned = 0;
shrink_zones(zonelist, sc);
total_scanned += sc->nr_scanned;
if (sc->nr_reclaimed >= sc->nr_to_reclaim)
break;
if (sc->compaction_ready)
break;
/*
* If we're getting trouble reclaiming, start doing
* writepage even in laptop mode.
*/
if (sc->priority < DEF_PRIORITY - 2)
sc->may_writepage = 1;
/*
* Try to write back as many pages as we just scanned. This
* tends to cause slow streaming writers to write data to the
* disk smoothly, at the dirtying rate, which is nice. But
* that's undesirable in laptop mode, where we *want* lumpy
* writeout. So in laptop mode, write out the whole world.
*/
writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
if (total_scanned > writeback_threshold) {
wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
WB_REASON_TRY_TO_FREE_PAGES);
sc->may_writepage = 1;
}
} while (--sc->priority >= 0);
delayacct_freepages_end();
if (sc->nr_reclaimed)
return sc->nr_reclaimed;
/* Aborted reclaim to try compaction? don't OOM, then */
if (sc->compaction_ready)
return 1;
/* Untapped cgroup reserves? Don't OOM, retry. */
if (!sc->may_thrash) {
sc->priority = initial_priority;
sc->may_thrash = 1;
goto retry;
}
return 0;
}
static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
{
struct zone *zone;
unsigned long pfmemalloc_reserve = 0;
unsigned long free_pages = 0;
int i;
bool wmark_ok;
for (i = 0; i <= ZONE_NORMAL; i++) {
zone = &pgdat->node_zones[i];
if (!populated_zone(zone) ||
zone_reclaimable_pages(zone) == 0)
continue;
pfmemalloc_reserve += min_wmark_pages(zone);
free_pages += zone_page_state(zone, NR_FREE_PAGES);
}
/* If there are no reserves (unexpected config) then do not throttle */
if (!pfmemalloc_reserve)
return true;
wmark_ok = free_pages > pfmemalloc_reserve / 2;
/* kswapd must be awake if processes are being throttled */
if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
pgdat->classzone_idx = min(pgdat->classzone_idx,
(enum zone_type)ZONE_NORMAL);
wake_up_interruptible(&pgdat->kswapd_wait);
}
return wmark_ok;
}
/*
* Throttle direct reclaimers if backing storage is backed by the network
* and the PFMEMALLOC reserve for the preferred node is getting dangerously
* depleted. kswapd will continue to make progress and wake the processes
* when the low watermark is reached.
*
* Returns true if a fatal signal was delivered during throttling. If this
* happens, the page allocator should not consider triggering the OOM killer.
*/
static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
nodemask_t *nodemask)
{
struct zoneref *z;
struct zone *zone;
pg_data_t *pgdat = NULL;
/*
* Kernel threads should not be throttled as they may be indirectly
* responsible for cleaning pages necessary for reclaim to make forward
* progress. kjournald for example may enter direct reclaim while
* committing a transaction where throttling it could forcing other
* processes to block on log_wait_commit().
*/
if (current->flags & PF_KTHREAD)
goto out;
/*
* If a fatal signal is pending, this process should not throttle.
* It should return quickly so it can exit and free its memory
*/
if (fatal_signal_pending(current))
goto out;
/*
* Check if the pfmemalloc reserves are ok by finding the first node
* with a usable ZONE_NORMAL or lower zone. The expectation is that
* GFP_KERNEL will be required for allocating network buffers when
* swapping over the network so ZONE_HIGHMEM is unusable.
*
* Throttling is based on the first usable node and throttled processes
* wait on a queue until kswapd makes progress and wakes them. There
* is an affinity then between processes waking up and where reclaim
* progress has been made assuming the process wakes on the same node.
* More importantly, processes running on remote nodes will not compete
* for remote pfmemalloc reserves and processes on different nodes
* should make reasonable progress.
*/
for_each_zone_zonelist_nodemask(zone, z, zonelist,
gfp_zone(gfp_mask), nodemask) {
if (zone_idx(zone) > ZONE_NORMAL)
continue;
/* Throttle based on the first usable node */
pgdat = zone->zone_pgdat;
if (pfmemalloc_watermark_ok(pgdat))
goto out;
break;
}
/* If no zone was usable by the allocation flags then do not throttle */
if (!pgdat)
goto out;
/* Account for the throttling */
count_vm_event(PGSCAN_DIRECT_THROTTLE);
/*
* If the caller cannot enter the filesystem, it's possible that it
* is due to the caller holding an FS lock or performing a journal
* transaction in the case of a filesystem like ext[3|4]. In this case,
* it is not safe to block on pfmemalloc_wait as kswapd could be
* blocked waiting on the same lock. Instead, throttle for up to a
* second before continuing.
*/
if (!(gfp_mask & __GFP_FS)) {
wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
pfmemalloc_watermark_ok(pgdat), HZ);
goto check_pending;
}
/* Throttle until kswapd wakes the process */
wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
pfmemalloc_watermark_ok(pgdat));
check_pending:
if (fatal_signal_pending(current))
return true;
out:
return false;
}
unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
gfp_t gfp_mask, nodemask_t *nodemask)
{
unsigned long nr_reclaimed;
struct scan_control sc = {
.nr_to_reclaim = SWAP_CLUSTER_MAX,
.gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
.order = order,
.nodemask = nodemask,
.priority = DEF_PRIORITY,
.may_writepage = !laptop_mode,
.may_unmap = 1,
.may_swap = 1,
};
/*
* Do not enter reclaim if fatal signal was delivered while throttled.
* 1 is returned so that the page allocator does not OOM kill at this
* point.
*/
if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask))
return 1;
trace_mm_vmscan_direct_reclaim_begin(order,
sc.may_writepage,
gfp_mask);
nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
return nr_reclaimed;
}
#ifdef CONFIG_MEMCG
unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
gfp_t gfp_mask, bool noswap,
struct zone *zone,
unsigned long *nr_scanned)
{
struct scan_control sc = {
.nr_to_reclaim = SWAP_CLUSTER_MAX,
.target_mem_cgroup = memcg,
.may_writepage = !laptop_mode,
.may_unmap = 1,
.may_swap = !noswap,
};
unsigned long lru_pages;
sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
sc.may_writepage,
sc.gfp_mask);
/*
* NOTE: Although we can get the priority field, using it
* here is not a good idea, since it limits the pages we can scan.
* if we don't reclaim here, the shrink_zone from balance_pgdat
* will pick up pages from other mem cgroup's as well. We hack
* the priority and make it zero.
*/
shrink_zone_memcg(zone, memcg, &sc, &lru_pages);
trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
*nr_scanned = sc.nr_scanned;
return sc.nr_reclaimed;
}
unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
unsigned long nr_pages,
gfp_t gfp_mask,
bool may_swap)
{
struct zonelist *zonelist;
unsigned long nr_reclaimed;
int nid;
struct scan_control sc = {
.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
.target_mem_cgroup = memcg,
.priority = DEF_PRIORITY,
.may_writepage = !laptop_mode,
.may_unmap = 1,
.may_swap = may_swap,
};
/*
* Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
* take care of from where we get pages. So the node where we start the
* scan does not need to be the current node.
*/
nid = mem_cgroup_select_victim_node(memcg);
zonelist = NODE_DATA(nid)->node_zonelists;
trace_mm_vmscan_memcg_reclaim_begin(0,
sc.may_writepage,
sc.gfp_mask);
nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
return nr_reclaimed;
}
#endif
static void age_active_anon(struct zone *zone, struct scan_control *sc)
{
struct mem_cgroup *memcg;
if (!total_swap_pages)
return;
memcg = mem_cgroup_iter(NULL, NULL, NULL);
do {
struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
if (inactive_list_is_low(lruvec, false))
shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
sc, LRU_ACTIVE_ANON);
memcg = mem_cgroup_iter(NULL, memcg, NULL);
} while (memcg);
}
static bool zone_balanced(struct zone *zone, int order, bool highorder,
unsigned long balance_gap, int classzone_idx)
{
unsigned long mark = high_wmark_pages(zone) + balance_gap;
/*
* When checking from pgdat_balanced(), kswapd should stop and sleep
* when it reaches the high order-0 watermark and let kcompactd take
* over. Other callers such as wakeup_kswapd() want to determine the
* true high-order watermark.
*/
if (IS_ENABLED(CONFIG_COMPACTION) && !highorder) {
mark += (1UL << order);
order = 0;
}
return zone_watermark_ok_safe(zone, order, mark, classzone_idx);
}
/*
* pgdat_balanced() is used when checking if a node is balanced.
*
* For order-0, all zones must be balanced!
*
* For high-order allocations only zones that meet watermarks and are in a
* zone allowed by the callers classzone_idx are added to balanced_pages. The
* total of balanced pages must be at least 25% of the zones allowed by
* classzone_idx for the node to be considered balanced. Forcing all zones to
* be balanced for high orders can cause excessive reclaim when there are
* imbalanced zones.
* The choice of 25% is due to
* o a 16M DMA zone that is balanced will not balance a zone on any
* reasonable sized machine
* o On all other machines, the top zone must be at least a reasonable
* percentage of the middle zones. For example, on 32-bit x86, highmem
* would need to be at least 256M for it to be balance a whole node.
* Similarly, on x86-64 the Normal zone would need to be at least 1G
* to balance a node on its own. These seemed like reasonable ratios.
*/
static bool pgdat_balanced(pg_data_t *pgdat, int order, int classzone_idx)
{
unsigned long managed_pages = 0;
unsigned long balanced_pages = 0;
int i;
/* Check the watermark levels */
for (i = 0; i <= classzone_idx; i++) {
struct zone *zone = pgdat->node_zones + i;
if (!populated_zone(zone))
continue;
managed_pages += zone->managed_pages;
/*
* A special case here:
*
* balance_pgdat() skips over all_unreclaimable after
* DEF_PRIORITY. Effectively, it considers them balanced so
* they must be considered balanced here as well!
*/
if (!zone_reclaimable(zone)) {
balanced_pages += zone->managed_pages;
continue;
}
if (zone_balanced(zone, order, false, 0, i))
balanced_pages += zone->managed_pages;
else if (!order)
return false;
}
if (order)
return balanced_pages >= (managed_pages >> 2);
else
return true;
}
/*
* Prepare kswapd for sleeping. This verifies that there are no processes
* waiting in throttle_direct_reclaim() and that watermarks have been met.
*
* Returns true if kswapd is ready to sleep
*/
static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
int classzone_idx)
{
/* If a direct reclaimer woke kswapd within HZ/10, it's premature */
if (remaining)
return false;
/*
* The throttled processes are normally woken up in balance_pgdat() as
* soon as pfmemalloc_watermark_ok() is true. But there is a potential
* race between when kswapd checks the watermarks and a process gets
* throttled. There is also a potential race if processes get
* throttled, kswapd wakes, a large process exits thereby balancing the
* zones, which causes kswapd to exit balance_pgdat() before reaching
* the wake up checks. If kswapd is going to sleep, no process should
* be sleeping on pfmemalloc_wait, so wake them now if necessary. If
* the wake up is premature, processes will wake kswapd and get
* throttled again. The difference from wake ups in balance_pgdat() is
* that here we are under prepare_to_wait().
*/
if (waitqueue_active(&pgdat->pfmemalloc_wait))
wake_up_all(&pgdat->pfmemalloc_wait);
return pgdat_balanced(pgdat, order, classzone_idx);
}
/*
* kswapd shrinks the zone by the number of pages required to reach
* the high watermark.
*
* Returns true if kswapd scanned at least the requested number of pages to
* reclaim or if the lack of progress was due to pages under writeback.
* This is used to determine if the scanning priority needs to be raised.
*/
static bool kswapd_shrink_zone(struct zone *zone,
int classzone_idx,
struct scan_control *sc)
{
unsigned long balance_gap;
bool lowmem_pressure;
/* Reclaim above the high watermark. */
sc->nr_to_reclaim = max(SWAP_CLUSTER_MAX, high_wmark_pages(zone));
/*
* We put equal pressure on every zone, unless one zone has way too
* many pages free already. The "too many pages" is defined as the
* high wmark plus a "gap" where the gap is either the low
* watermark or 1% of the zone, whichever is smaller.
*/
balance_gap = min(low_wmark_pages(zone), DIV_ROUND_UP(
zone->managed_pages, KSWAPD_ZONE_BALANCE_GAP_RATIO));
/*
* If there is no low memory pressure or the zone is balanced then no
* reclaim is necessary
*/
lowmem_pressure = (buffer_heads_over_limit && is_highmem(zone));
if (!lowmem_pressure && zone_balanced(zone, sc->order, false,
balance_gap, classzone_idx))
return true;
shrink_zone(zone, sc, zone_idx(zone) == classzone_idx);
clear_bit(ZONE_WRITEBACK, &zone->flags);
/*
* If a zone reaches its high watermark, consider it to be no longer
* congested. It's possible there are dirty pages backed by congested
* BDIs but as pressure is relieved, speculatively avoid congestion
* waits.
*/
if (zone_reclaimable(zone) &&
zone_balanced(zone, sc->order, false, 0, classzone_idx)) {
clear_bit(ZONE_CONGESTED, &zone->flags);
clear_bit(ZONE_DIRTY, &zone->flags);
}
return sc->nr_scanned >= sc->nr_to_reclaim;
}
/*
* For kswapd, balance_pgdat() will work across all this node's zones until
* they are all at high_wmark_pages(zone).
*
* Returns the highest zone idx kswapd was reclaiming at
*
* There is special handling here for zones which are full of pinned pages.
* This can happen if the pages are all mlocked, or if they are all used by
* device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb.
* What we do is to detect the case where all pages in the zone have been
* scanned twice and there has been zero successful reclaim. Mark the zone as
* dead and from now on, only perform a short scan. Basically we're polling
* the zone for when the problem goes away.
*
* kswapd scans the zones in the highmem->normal->dma direction. It skips
* zones which have free_pages > high_wmark_pages(zone), but once a zone is
* found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
* lower zones regardless of the number of free pages in the lower zones. This
* interoperates with the page allocator fallback scheme to ensure that aging
* of pages is balanced across the zones.
*/
static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
{
int i;
int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
unsigned long nr_soft_reclaimed;
unsigned long nr_soft_scanned;
struct scan_control sc = {
.gfp_mask = GFP_KERNEL,
.order = order,
.priority = DEF_PRIORITY,
.may_writepage = !laptop_mode,
.may_unmap = 1,
.may_swap = 1,
};
count_vm_event(PAGEOUTRUN);
do {
bool raise_priority = true;
sc.nr_reclaimed = 0;
/*
* Scan in the highmem->dma direction for the highest
* zone which needs scanning
*/
for (i = pgdat->nr_zones - 1; i >= 0; i--) {
struct zone *zone = pgdat->node_zones + i;
if (!populated_zone(zone))
continue;
if (sc.priority != DEF_PRIORITY &&
!zone_reclaimable(zone))
continue;
/*
* Do some background aging of the anon list, to give
* pages a chance to be referenced before reclaiming.
*/
age_active_anon(zone, &sc);
/*
* If the number of buffer_heads in the machine
* exceeds the maximum allowed level and this node
* has a highmem zone, force kswapd to reclaim from
* it to relieve lowmem pressure.
*/
if (buffer_heads_over_limit && is_highmem_idx(i)) {
end_zone = i;
break;
}
if (!zone_balanced(zone, order, false, 0, 0)) {
end_zone = i;
break;
} else {
/*
* If balanced, clear the dirty and congested
* flags
*/
clear_bit(ZONE_CONGESTED, &zone->flags);
clear_bit(ZONE_DIRTY, &zone->flags);
}
}
if (i < 0)
goto out;
/*
* If we're getting trouble reclaiming, start doing writepage
* even in laptop mode.
*/
if (sc.priority < DEF_PRIORITY - 2)
sc.may_writepage = 1;
/*
* Now scan the zone in the dma->highmem direction, stopping
* at the last zone which needs scanning.
*
* We do this because the page allocator works in the opposite
* direction. This prevents the page allocator from allocating
* pages behind kswapd's direction of progress, which would
* cause too much scanning of the lower zones.
*/
for (i = 0; i <= end_zone; i++) {
struct zone *zone = pgdat->node_zones + i;
if (!populated_zone(zone))
continue;
if (sc.priority != DEF_PRIORITY &&
!zone_reclaimable(zone))
continue;
sc.nr_scanned = 0;
nr_soft_scanned = 0;
/*
* Call soft limit reclaim before calling shrink_zone.
*/
nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
order, sc.gfp_mask,
&nr_soft_scanned);
sc.nr_reclaimed += nr_soft_reclaimed;
/*
* There should be no need to raise the scanning
* priority if enough pages are already being scanned
* that that high watermark would be met at 100%
* efficiency.
*/
if (kswapd_shrink_zone(zone, end_zone, &sc))
raise_priority = false;
}
/*
* If the low watermark is met there is no need for processes
* to be throttled on pfmemalloc_wait as they should not be
* able to safely make forward progress. Wake them
*/
if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
pfmemalloc_watermark_ok(pgdat))
wake_up_all(&pgdat->pfmemalloc_wait);
/* Check if kswapd should be suspending */
if (try_to_freeze() || kthread_should_stop())
break;
/*
* Raise priority if scanning rate is too low or there was no
* progress in reclaiming pages
*/
if (raise_priority || !sc.nr_reclaimed)
sc.priority--;
} while (sc.priority >= 1 &&
!pgdat_balanced(pgdat, order, classzone_idx));
out:
/*
* Return the highest zone idx we were reclaiming at so
* prepare_kswapd_sleep() makes the same decisions as here.
*/
return end_zone;
}
static void kswapd_try_to_sleep(pg_data_t *pgdat, int order,
int classzone_idx, int balanced_classzone_idx)
{
long remaining = 0;
DEFINE_WAIT(wait);
if (freezing(current) || kthread_should_stop())
return;
prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
/* Try to sleep for a short interval */
if (prepare_kswapd_sleep(pgdat, order, remaining,
balanced_classzone_idx)) {
/*
* Compaction records what page blocks it recently failed to
* isolate pages from and skips them in the future scanning.
* When kswapd is going to sleep, it is reasonable to assume
* that pages and compaction may succeed so reset the cache.
*/
reset_isolation_suitable(pgdat);
/*
* We have freed the memory, now we should compact it to make
* allocation of the requested order possible.
*/
wakeup_kcompactd(pgdat, order, classzone_idx);
remaining = schedule_timeout(HZ/10);
finish_wait(&pgdat->kswapd_wait, &wait);
prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
}
/*
* After a short sleep, check if it was a premature sleep. If not, then
* go fully to sleep until explicitly woken up.
*/
if (prepare_kswapd_sleep(pgdat, order, remaining,
balanced_classzone_idx)) {
trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
/*
* vmstat counters are not perfectly accurate and the estimated
* value for counters such as NR_FREE_PAGES can deviate from the
* true value by nr_online_cpus * threshold. To avoid the zone
* watermarks being breached while under pressure, we reduce the
* per-cpu vmstat threshold while kswapd is awake and restore
* them before going back to sleep.
*/
set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
if (!kthread_should_stop())
schedule();
set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
} else {
if (remaining)
count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
else
count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
}
finish_wait(&pgdat->kswapd_wait, &wait);
}
/*
* The background pageout daemon, started as a kernel thread
* from the init process.
*
* This basically trickles out pages so that we have _some_
* free memory available even if there is no other activity
* that frees anything up. This is needed for things like routing
* etc, where we otherwise might have all activity going on in
* asynchronous contexts that cannot page things out.
*
* If there are applications that are active memory-allocators
* (most normal use), this basically shouldn't matter.
*/
static int kswapd(void *p)
{
unsigned long order, new_order;
int classzone_idx, new_classzone_idx;
int balanced_classzone_idx;
pg_data_t *pgdat = (pg_data_t*)p;
struct task_struct *tsk = current;
struct reclaim_state reclaim_state = {
.reclaimed_slab = 0,
};
const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
lockdep_set_current_reclaim_state(GFP_KERNEL);
if (!cpumask_empty(cpumask))
set_cpus_allowed_ptr(tsk, cpumask);
current->reclaim_state = &reclaim_state;
/*
* Tell the memory management that we're a "memory allocator",
* and that if we need more memory we should get access to it
* regardless (see "__alloc_pages()"). "kswapd" should
* never get caught in the normal page freeing logic.
*
* (Kswapd normally doesn't need memory anyway, but sometimes
* you need a small amount of memory in order to be able to
* page out something else, and this flag essentially protects
* us from recursively trying to free more memory as we're
* trying to free the first piece of memory in the first place).
*/
tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
set_freezable();
order = new_order = 0;
classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
balanced_classzone_idx = classzone_idx;
for ( ; ; ) {
bool ret;
/*
* While we were reclaiming, there might have been another
* wakeup, so check the values.
*/
new_order = pgdat->kswapd_max_order;
new_classzone_idx = pgdat->classzone_idx;
pgdat->kswapd_max_order = 0;
pgdat->classzone_idx = pgdat->nr_zones - 1;
if (order < new_order || classzone_idx > new_classzone_idx) {
/*
* Don't sleep if someone wants a larger 'order'
* allocation or has tigher zone constraints
*/
order = new_order;
classzone_idx = new_classzone_idx;
} else {
kswapd_try_to_sleep(pgdat, order, classzone_idx,
balanced_classzone_idx);
order = pgdat->kswapd_max_order;
classzone_idx = pgdat->classzone_idx;
new_order = order;
new_classzone_idx = classzone_idx;
pgdat->kswapd_max_order = 0;
pgdat->classzone_idx = pgdat->nr_zones - 1;
}
ret = try_to_freeze();
if (kthread_should_stop())
break;
/*
* We can speed up thawing tasks if we don't call balance_pgdat
* after returning from the refrigerator
*/
if (!ret) {
trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
balanced_classzone_idx = balance_pgdat(pgdat, order,
classzone_idx);
}
}
tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD);
current->reclaim_state = NULL;
lockdep_clear_current_reclaim_state();
return 0;
}
/*
* A zone is low on free memory, so wake its kswapd task to service it.
*/
void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
{
pg_data_t *pgdat;
if (!populated_zone(zone))
return;
if (!cpuset_zone_allowed(zone, GFP_KERNEL | __GFP_HARDWALL))
return;
pgdat = zone->zone_pgdat;
if (pgdat->kswapd_max_order < order) {
pgdat->kswapd_max_order = order;
pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
}
if (!waitqueue_active(&pgdat->kswapd_wait))
return;
if (zone_balanced(zone, order, true, 0, 0))
return;
trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
wake_up_interruptible(&pgdat->kswapd_wait);
}
#ifdef CONFIG_HIBERNATION
/*
* Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
* freed pages.
*
* Rather than trying to age LRUs the aim is to preserve the overall
* LRU order by reclaiming preferentially
* inactive > active > active referenced > active mapped
*/
unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
{
struct reclaim_state reclaim_state;
struct scan_control sc = {
.nr_to_reclaim = nr_to_reclaim,
.gfp_mask = GFP_HIGHUSER_MOVABLE,
.priority = DEF_PRIORITY,
.may_writepage = 1,
.may_unmap = 1,
.may_swap = 1,
.hibernation_mode = 1,
};
struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
struct task_struct *p = current;
unsigned long nr_reclaimed;
p->flags |= PF_MEMALLOC;
lockdep_set_current_reclaim_state(sc.gfp_mask);
reclaim_state.reclaimed_slab = 0;
p->reclaim_state = &reclaim_state;
nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
p->reclaim_state = NULL;
lockdep_clear_current_reclaim_state();
p->flags &= ~PF_MEMALLOC;
return nr_reclaimed;
}
#endif /* CONFIG_HIBERNATION */
/* It's optimal to keep kswapds on the same CPUs as their memory, but
not required for correctness. So if the last cpu in a node goes
away, we get changed to run anywhere: as the first one comes back,
restore their cpu bindings. */
static int cpu_callback(struct notifier_block *nfb, unsigned long action,
void *hcpu)
{
int nid;
if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
for_each_node_state(nid, N_MEMORY) {
pg_data_t *pgdat = NODE_DATA(nid);
const struct cpumask *mask;
mask = cpumask_of_node(pgdat->node_id);
if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
/* One of our CPUs online: restore mask */
set_cpus_allowed_ptr(pgdat->kswapd, mask);
}
}
return NOTIFY_OK;
}
/*
* This kswapd start function will be called by init and node-hot-add.
* On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
*/
int kswapd_run(int nid)
{
pg_data_t *pgdat = NODE_DATA(nid);
int ret = 0;
if (pgdat->kswapd)
return 0;
pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
if (IS_ERR(pgdat->kswapd)) {
/* failure at boot is fatal */
BUG_ON(system_state == SYSTEM_BOOTING);
pr_err("Failed to start kswapd on node %d\n", nid);
ret = PTR_ERR(pgdat->kswapd);
pgdat->kswapd = NULL;
}
return ret;
}
/*
* Called by memory hotplug when all memory in a node is offlined. Caller must
* hold mem_hotplug_begin/end().
*/
void kswapd_stop(int nid)
{
struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
if (kswapd) {
kthread_stop(kswapd);
NODE_DATA(nid)->kswapd = NULL;
}
}
static int __init kswapd_init(void)
{
int nid;
swap_setup();
for_each_node_state(nid, N_MEMORY)
kswapd_run(nid);
hotcpu_notifier(cpu_callback, 0);
return 0;
}
module_init(kswapd_init)
#ifdef CONFIG_NUMA
/*
* Zone reclaim mode
*
* If non-zero call zone_reclaim when the number of free pages falls below
* the watermarks.
*/
int zone_reclaim_mode __read_mostly;
#define RECLAIM_OFF 0
#define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */
#define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */
#define RECLAIM_UNMAP (1<<2) /* Unmap pages during reclaim */
/*
* Priority for ZONE_RECLAIM. This determines the fraction of pages
* of a node considered for each zone_reclaim. 4 scans 1/16th of
* a zone.
*/
#define ZONE_RECLAIM_PRIORITY 4
/*
* Percentage of pages in a zone that must be unmapped for zone_reclaim to
* occur.
*/
int sysctl_min_unmapped_ratio = 1;
/*
* If the number of slab pages in a zone grows beyond this percentage then
* slab reclaim needs to occur.
*/
int sysctl_min_slab_ratio = 5;
static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
{
unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
zone_page_state(zone, NR_ACTIVE_FILE);
/*
* It's possible for there to be more file mapped pages than
* accounted for by the pages on the file LRU lists because
* tmpfs pages accounted for as ANON can also be FILE_MAPPED
*/
return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
}
/* Work out how many page cache pages we can reclaim in this reclaim_mode */
static unsigned long zone_pagecache_reclaimable(struct zone *zone)
{
unsigned long nr_pagecache_reclaimable;
unsigned long delta = 0;
/*
* If RECLAIM_UNMAP is set, then all file pages are considered
* potentially reclaimable. Otherwise, we have to worry about
* pages like swapcache and zone_unmapped_file_pages() provides
* a better estimate
*/
if (zone_reclaim_mode & RECLAIM_UNMAP)
nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
else
nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
/* If we can't clean pages, remove dirty pages from consideration */
if (!(zone_reclaim_mode & RECLAIM_WRITE))
delta += zone_page_state(zone, NR_FILE_DIRTY);
/* Watch for any possible underflows due to delta */
if (unlikely(delta > nr_pagecache_reclaimable))
delta = nr_pagecache_reclaimable;
return nr_pagecache_reclaimable - delta;
}
/*
* Try to free up some pages from this zone through reclaim.
*/
static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
{
/* Minimum pages needed in order to stay on node */
const unsigned long nr_pages = 1 << order;
struct task_struct *p = current;
struct reclaim_state reclaim_state;
struct scan_control sc = {
.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
.gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
.order = order,
.priority = ZONE_RECLAIM_PRIORITY,
.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
.may_unmap = !!(zone_reclaim_mode & RECLAIM_UNMAP),
.may_swap = 1,
};
cond_resched();
/*
* We need to be able to allocate from the reserves for RECLAIM_UNMAP
* and we also need to be able to write out pages for RECLAIM_WRITE
* and RECLAIM_UNMAP.
*/
p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
lockdep_set_current_reclaim_state(gfp_mask);
reclaim_state.reclaimed_slab = 0;
p->reclaim_state = &reclaim_state;
if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
/*
* Free memory by calling shrink zone with increasing
* priorities until we have enough memory freed.
*/
do {
shrink_zone(zone, &sc, true);
} while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
}
p->reclaim_state = NULL;
current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
lockdep_clear_current_reclaim_state();
return sc.nr_reclaimed >= nr_pages;
}
int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
{
int node_id;
int ret;
/*
* Zone reclaim reclaims unmapped file backed pages and
* slab pages if we are over the defined limits.
*
* A small portion of unmapped file backed pages is needed for
* file I/O otherwise pages read by file I/O will be immediately
* thrown out if the zone is overallocated. So we do not reclaim
* if less than a specified percentage of the zone is used by
* unmapped file backed pages.
*/
if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
return ZONE_RECLAIM_FULL;
if (!zone_reclaimable(zone))
return ZONE_RECLAIM_FULL;
/*
* Do not scan if the allocation should not be delayed.
*/
if (!gfpflags_allow_blocking(gfp_mask) || (current->flags & PF_MEMALLOC))
return ZONE_RECLAIM_NOSCAN;
/*
* Only run zone reclaim on the local zone or on zones that do not
* have associated processors. This will favor the local processor
* over remote processors and spread off node memory allocations
* as wide as possible.
*/
node_id = zone_to_nid(zone);
if (node_state(node_id, N_CPU) && node_id != numa_node_id())
return ZONE_RECLAIM_NOSCAN;
if (test_and_set_bit(ZONE_RECLAIM_LOCKED, &zone->flags))
return ZONE_RECLAIM_NOSCAN;
ret = __zone_reclaim(zone, gfp_mask, order);
clear_bit(ZONE_RECLAIM_LOCKED, &zone->flags);
if (!ret)
count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
return ret;
}
#endif
/*
* page_evictable - test whether a page is evictable
* @page: the page to test
*
* Test whether page is evictable--i.e., should be placed on active/inactive
* lists vs unevictable list.
*
* Reasons page might not be evictable:
* (1) page's mapping marked unevictable
* (2) page is part of an mlocked VMA
*
*/
int page_evictable(struct page *page)
{
return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
}
#ifdef CONFIG_SHMEM
/**
* check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list
* @pages: array of pages to check
* @nr_pages: number of pages to check
*
* Checks pages for evictability and moves them to the appropriate lru list.
*
* This function is only used for SysV IPC SHM_UNLOCK.
*/
void check_move_unevictable_pages(struct page **pages, int nr_pages)
{
struct lruvec *lruvec;
struct zone *zone = NULL;
int pgscanned = 0;
int pgrescued = 0;
int i;
for (i = 0; i < nr_pages; i++) {
struct page *page = pages[i];
struct zone *pagezone;
pgscanned++;
pagezone = page_zone(page);
if (pagezone != zone) {
if (zone)
spin_unlock_irq(&zone->lru_lock);
zone = pagezone;
spin_lock_irq(&zone->lru_lock);
}
lruvec = mem_cgroup_page_lruvec(page, zone);
if (!PageLRU(page) || !PageUnevictable(page))
continue;
if (page_evictable(page)) {
enum lru_list lru = page_lru_base_type(page);
VM_BUG_ON_PAGE(PageActive(page), page);
ClearPageUnevictable(page);
del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
add_page_to_lru_list(page, lruvec, lru);
pgrescued++;
}
}
if (zone) {
__count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
__count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
spin_unlock_irq(&zone->lru_lock);
}
}
#endif /* CONFIG_SHMEM */
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