/*
* 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/debugfs.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;
};
#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
#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
static unsigned long zone_reclaimable_pages(struct zone *zone)
{
unsigned long nr;
nr = zone_page_state(zone, NR_ACTIVE_FILE) +
zone_page_state(zone, NR_INACTIVE_FILE);
if (get_nr_swap_pages() > 0)
nr += zone_page_state(zone, NR_ACTIVE_ANON) +
zone_page_state(zone, NR_INACTIVE_ANON);
return nr;
}
bool zone_reclaimable(struct zone *zone)
{
return zone_page_state(zone, NR_PAGES_SCANNED) <
zone_reclaimable_pages(zone) * 6;
}
static unsigned long get_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);
}
struct dentry *debug_file;
static int debug_shrinker_show(struct seq_file *s, void *unused)
{
struct shrinker *shrinker;
struct shrink_control sc;
sc.gfp_mask = -1;
sc.nr_to_scan = 0;
down_read(&shrinker_rwsem);
list_for_each_entry(shrinker, &shrinker_list, list) {
int num_objs;
num_objs = shrinker->count_objects(shrinker, &sc);
seq_printf(s, "%pf %d\n", shrinker->scan_objects, num_objs);
}
up_read(&shrinker_rwsem);
return 0;
}
static int debug_shrinker_open(struct inode *inode, struct file *file)
{
return single_open(file, debug_shrinker_show, inode->i_private);
}
static const struct file_operations debug_shrinker_fops = {
.open = debug_shrinker_open,
.read = seq_read,
.llseek = seq_lseek,
.release = single_release,
};
/*
* Add a shrinker callback to be called from the vm.
*/
int register_shrinker(struct shrinker *shrinker)
{
size_t size = sizeof(*shrinker->nr_deferred);
/*
* If we only have one possible node in the system anyway, save
* ourselves the trouble and disable NUMA aware behavior. This way we
* will save memory and some small loop time later.
*/
if (nr_node_ids == 1)
shrinker->flags &= ~SHRINKER_NUMA_AWARE;
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);
static int __init add_shrinker_debug(void)
{
debugfs_create_file("shrinker", 0644, NULL, NULL,
&debug_shrinker_fops);
return 0;
}
late_initcall(add_shrinker_debug);
/*
* 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 all shrinkers
* are called, and memcg aware shrinkers are supposed to scan the
* global list then.
*
* @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_is_active(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 (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, trace_reclaim_flags(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;
struct mem_cgroup *memcg;
BUG_ON(!PageLocked(page));
BUG_ON(mapping != page_mapping(page));
memcg = mem_cgroup_begin_page_stat(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->_count.
*
* Note that if SetPageDirty is always performed via set_page_dirty,
* and thus under tree_lock, then this ordering is not required.
*/
if (!page_freeze_refs(page, 2))
goto cannot_free;
/* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
if (unlikely(PageDirty(page))) {
page_unfreeze_refs(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);
mem_cgroup_end_page_stat(memcg);
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.
*/
if (reclaimed && page_is_file_cache(page) &&
!mapping_exiting(mapping))
shadow = workingset_eviction(mapping, page);
__delete_from_page_cache(page, shadow, memcg);
spin_unlock_irqrestore(&mapping->tree_lock, flags);
mem_cgroup_end_page_stat(memcg);
if (freepage != NULL)
freepage(page);
}
return 1;
cannot_free:
spin_unlock_irqrestore(&mapping->tree_lock, flags);
mem_cgroup_end_page_stat(memcg);
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_unfreeze_refs(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;
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;
may_enter_fs = 1;
/* Adding to swap updated mapping */
mapping = page_mapping(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 (try_to_unmap(page,
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_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;
}
}
}
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.
*/
__clear_page_locked(page);
free_it:
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) && vm_swap_full())
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) &&
!isolated_balloon_page(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;
int nr_pages;
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_pages = hpage_nr_pages(page);
mem_cgroup_update_lru_size(lruvec, lru, -nr_pages);
list_move(&page->lru, dst);
nr_taken += nr_pages;
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);
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);
__mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
__mod_zone_page_state(zone, NR_ISOLATED_ANON + 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);
reclaim_stat->recent_scanned[file] += nr_taken;
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->zone_pgdat->node_id,
zone_idx(zone),
nr_scanned, nr_reclaimed,
sc->priority,
trace_shrink_flags(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->_count 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);
mem_cgroup_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);
}
}
__mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
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);
if (global_reclaim(sc))
__mod_zone_page_state(zone, NR_PAGES_SCANNED, nr_scanned);
reclaim_stat->recent_scanned[file] += nr_taken;
__count_zone_vm_events(PGREFILL, zone, nr_scanned);
__mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
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);
}
#ifdef CONFIG_SWAP
static bool inactive_anon_is_low_global(struct zone *zone)
{
unsigned long active, inactive;
active = zone_page_state(zone, NR_ACTIVE_ANON);
inactive = zone_page_state(zone, NR_INACTIVE_ANON);
return inactive * zone->inactive_ratio < active;
}
/**
* inactive_anon_is_low - check if anonymous pages need to be deactivated
* @lruvec: LRU vector to check
*
* Returns true if the zone does not have enough inactive anon pages,
* meaning some active anon pages need to be deactivated.
*/
static bool inactive_anon_is_low(struct lruvec *lruvec)
{
/*
* If we don't have swap space, anonymous page deactivation
* is pointless.
*/
if (!total_swap_pages)
return false;
if (!mem_cgroup_disabled())
return mem_cgroup_inactive_anon_is_low(lruvec);
return inactive_anon_is_low_global(lruvec_zone(lruvec));
}
#else
static inline bool inactive_anon_is_low(struct lruvec *lruvec)
{
return false;
}
#endif
/**
* inactive_file_is_low - check if file pages need to be deactivated
* @lruvec: LRU vector to check
*
* When the system is doing streaming IO, memory pressure here
* ensures that active file pages get deactivated, until more
* than half of the file pages are on the inactive list.
*
* Once we get to that situation, protect the system's working
* set from being evicted by disabling active file page aging.
*
* This uses a different ratio than the anonymous pages, because
* the page cache uses a use-once replacement algorithm.
*/
static bool inactive_file_is_low(struct lruvec *lruvec)
{
unsigned long inactive;
unsigned long active;
inactive = get_lru_size(lruvec, LRU_INACTIVE_FILE);
active = get_lru_size(lruvec, LRU_ACTIVE_FILE);
return active > inactive;
}
static bool inactive_list_is_low(struct lruvec *lruvec, enum lru_list lru)
{
if (is_file_lru(lru))
return inactive_file_is_low(lruvec);
else
return inactive_anon_is_low(lruvec);
}
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, 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, int swappiness,
struct scan_control *sc, unsigned long *nr,
unsigned long *lru_pages)
{
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_lruvec_online(lruvec))
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 || (get_nr_swap_pages() <= 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;
}
}
/*
* There is enough inactive page cache, do not reclaim
* anything from the anonymous working set right now.
*/
if (!inactive_file_is_low(lruvec)) {
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 = get_lru_size(lruvec, LRU_ACTIVE_ANON) +
get_lru_size(lruvec, LRU_INACTIVE_ANON);
file = get_lru_size(lruvec, LRU_ACTIVE_FILE) +
get_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 = get_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_lruvec(struct lruvec *lruvec, int swappiness,
struct scan_control *sc, unsigned long *lru_pages)
{
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, swappiness, 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_anon_is_low(lruvec))
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 scanned;
struct lruvec *lruvec;
int swappiness;
if (mem_cgroup_low(root, memcg)) {
if (!sc->may_thrash)
continue;
mem_cgroup_events(memcg, MEMCG_LOW, 1);
}
lruvec = mem_cgroup_zone_lruvec(zone, memcg);
swappiness = mem_cgroup_swappiness(memcg);
scanned = sc->nr_scanned;
shrink_lruvec(lruvec, swappiness, 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);
/*
* 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;
}
vmpressure(sc->gfp_mask, sc->target_mem_cgroup,
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)
{
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, 0);
/*
* 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, 0) == 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.
*
* Returns true if a zone was reclaimable.
*/
static bool 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);
bool reclaimable = false;
/*
* 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,
requested_highidx, 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)) {
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;
if (nr_soft_reclaimed)
reclaimable = true;
/* need some check for avoid more shrink_zone() */
}
if (shrink_zone(zone, sc, zone_idx(zone) == classzone_idx))
reclaimable = true;
if (global_reclaim(sc) &&
!reclaimable && zone_reclaimable(zone))
reclaimable = true;
}
/*
* Restore to original mask to avoid the impact on the caller if we
* promoted it to __GFP_HIGHMEM.
*/
sc->gfp_mask = orig_mask;
return reclaimable;
}
/*
* 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;
bool zones_reclaimable;
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;
zones_reclaimable = 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;
}
/* Any of the zones still reclaimable? Don't OOM. */
if (zones_reclaimable)
return 1;
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,
};
struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
int swappiness = mem_cgroup_swappiness(memcg);
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_lruvec(lruvec, swappiness, &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_anon_is_low(lruvec))
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,
unsigned long balance_gap, int classzone_idx)
{
if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone) +
balance_gap, classzone_idx))
return false;
if (IS_ENABLED(CONFIG_COMPACTION) && order && compaction_suitable(zone,
order, 0, classzone_idx) == COMPACT_SKIPPED)
return false;
return true;
}
/*
* 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, 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 *nr_attempted)
{
int testorder = sc->order;
unsigned long balance_gap;
bool lowmem_pressure;
/* Reclaim above the high watermark. */
sc->nr_to_reclaim = max(SWAP_CLUSTER_MAX, high_wmark_pages(zone));
/*
* Kswapd reclaims only single pages with compaction enabled. Trying
* too hard to reclaim until contiguous free pages have become
* available can hurt performance by evicting too much useful data
* from memory. Do not reclaim more than needed for compaction.
*/
if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
compaction_suitable(zone, sc->order, 0, classzone_idx)
!= COMPACT_SKIPPED)
testorder = 0;
/*
* 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, testorder,
balance_gap, classzone_idx))
return true;
shrink_zone(zone, sc, zone_idx(zone) == classzone_idx);
/* Account for the number of pages attempted to reclaim */
*nr_attempted += sc->nr_to_reclaim;
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, testorder, 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 final order 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 unsigned long 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 {
unsigned long nr_attempted = 0;
bool raise_priority = true;
bool pgdat_needs_compaction = (order > 0);
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, 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;
for (i = 0; i <= end_zone; i++) {
struct zone *zone = pgdat->node_zones + i;
if (!populated_zone(zone))
continue;
/*
* If any zone is currently balanced then kswapd will
* not call compaction as it is expected that the
* necessary pages are already available.
*/
if (pgdat_needs_compaction &&
zone_watermark_ok(zone, order,
low_wmark_pages(zone),
*classzone_idx, 0))
pgdat_needs_compaction = false;
}
/*
* 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, &nr_attempted))
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);
/*
* Fragmentation may mean that the system cannot be rebalanced
* for high-order allocations in all zones. If twice the
* allocation size has been reclaimed and the zones are still
* not balanced then recheck the watermarks at order-0 to
* prevent kswapd reclaiming excessively. Assume that a
* process requested a high-order can direct reclaim/compact.
*/
if (order && sc.nr_reclaimed >= 2UL << order)
order = sc.order = 0;
/* Check if kswapd should be suspending */
if (try_to_freeze() || kthread_should_stop())
break;
/*
* Compact if necessary and kswapd is reclaiming at least the
* high watermark number of pages as requsted
*/
if (pgdat_needs_compaction && sc.nr_reclaimed > nr_attempted)
compact_pgdat(pgdat, order);
/*
* 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 order we were reclaiming at so prepare_kswapd_sleep()
* makes a decision on the order we were last reclaiming at. However,
* if another caller entered the allocator slow path while kswapd
* was awake, order will remain at the higher level
*/
*classzone_idx = end_zone;
return order;
}
static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int 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, 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, 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);
/*
* 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);
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;
unsigned balanced_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;
balanced_order = 0;
classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
balanced_classzone_idx = classzone_idx;
for ( ; ; ) {
bool ret;
/*
* If the last balance_pgdat was unsuccessful it's unlikely a
* new request of a similar or harder type will succeed soon
* so consider going to sleep on the basis we reclaimed at
*/
if (balanced_classzone_idx >= new_classzone_idx &&
balanced_order == new_order) {
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, balanced_order,
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 = classzone_idx;
balanced_order = balance_pgdat(pgdat, order,
&balanced_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, 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 */