vmscan.c 114.9 KB
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// SPDX-License-Identifier: GPL-2.0
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/*
 *  linux/mm/vmscan.c
 *
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *
 *  Swap reorganised 29.12.95, Stephen Tweedie.
 *  kswapd added: 7.1.96  sct
 *  Removed kswapd_ctl limits, and swap out as many pages as needed
 *  to bring the system back to freepages.high: 2.4.97, Rik van Riel.
 *  Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
 *  Multiqueue VM started 5.8.00, Rik van Riel.
 */

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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

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#include <linux/mm.h>
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#include <linux/sched/mm.h>
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#include <linux/module.h>
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#include <linux/gfp.h>
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#include <linux/kernel_stat.h>
#include <linux/swap.h>
#include <linux/pagemap.h>
#include <linux/init.h>
#include <linux/highmem.h>
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#include <linux/vmpressure.h>
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#include <linux/vmstat.h>
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#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>
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#include <linux/compaction.h>
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#include <linux/notifier.h>
#include <linux/rwsem.h>
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#include <linux/delay.h>
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#include <linux/kthread.h>
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#include <linux/freezer.h>
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#include <linux/memcontrol.h>
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#include <linux/delayacct.h>
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#include <linux/sysctl.h>
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#include <linux/oom.h>
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#include <linux/prefetch.h>
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#include <linux/printk.h>
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#include <linux/dax.h>
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#include <asm/tlbflush.h>
#include <asm/div64.h>

#include <linux/swapops.h>
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#include <linux/balloon_compaction.h>
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#include "internal.h"

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#define CREATE_TRACE_POINTS
#include <trace/events/vmscan.h>

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struct scan_control {
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	/* How many pages shrink_list() should reclaim */
	unsigned long nr_to_reclaim;

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	/* This context's GFP mask */
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	gfp_t gfp_mask;
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	/* Allocation order */
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	int order;
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	/*
	 * Nodemask of nodes allowed by the caller. If NULL, all nodes
	 * are scanned.
	 */
	nodemask_t	*nodemask;
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	/*
	 * 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;
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	/* Scan (total_size >> priority) pages at once */
	int priority;

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	/* The highest zone to isolate pages for reclaim from */
	enum zone_type reclaim_idx;

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	/* Writepage batching in laptop mode; RECLAIM_WRITE */
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	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;

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	/*
	 * Cgroups are not reclaimed below their configured memory.low,
	 * unless we threaten to OOM. If any cgroups are skipped due to
	 * memory.low and nothing was reclaimed, go back for memory.low.
	 */
	unsigned int memcg_low_reclaim:1;
	unsigned int memcg_low_skipped:1;
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	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;
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};

#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;
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/*
 * The total number of pages which are beyond the high watermark within all
 * zones.
 */
unsigned long vm_total_pages;
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static LIST_HEAD(shrinker_list);
static DECLARE_RWSEM(shrinker_rwsem);

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#ifdef CONFIG_MEMCG
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static bool global_reclaim(struct scan_control *sc)
{
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	return !sc->target_mem_cgroup;
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}
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/**
 * 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
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	if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
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		return true;
#endif
	return false;
}
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#else
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static bool global_reclaim(struct scan_control *sc)
{
	return true;
}
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static bool sane_reclaim(struct scan_control *sc)
{
	return true;
}
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#endif

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/*
 * This misses isolated pages which are not accounted for to save counters.
 * As the data only determines if reclaim or compaction continues, it is
 * not expected that isolated pages will be a dominating factor.
 */
unsigned long zone_reclaimable_pages(struct zone *zone)
{
	unsigned long nr;

	nr = zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_FILE) +
		zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_FILE);
	if (get_nr_swap_pages() > 0)
		nr += zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_ANON) +
			zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_ANON);

	return nr;
}

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/**
 * lruvec_lru_size -  Returns the number of pages on the given LRU list.
 * @lruvec: lru vector
 * @lru: lru to use
 * @zone_idx: zones to consider (use MAX_NR_ZONES for the whole LRU list)
 */
unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru, int zone_idx)
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{
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	unsigned long lru_size;
	int zid;

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	if (!mem_cgroup_disabled())
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		lru_size = mem_cgroup_get_lru_size(lruvec, lru);
	else
		lru_size = node_page_state(lruvec_pgdat(lruvec), NR_LRU_BASE + lru);
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	for (zid = zone_idx + 1; zid < MAX_NR_ZONES; zid++) {
		struct zone *zone = &lruvec_pgdat(lruvec)->node_zones[zid];
		unsigned long size;
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		if (!managed_zone(zone))
			continue;

		if (!mem_cgroup_disabled())
			size = mem_cgroup_get_zone_lru_size(lruvec, lru, zid);
		else
			size = zone_page_state(&lruvec_pgdat(lruvec)->node_zones[zid],
				       NR_ZONE_LRU_BASE + lru);
		lru_size -= min(size, lru_size);
	}

	return lru_size;
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}

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/*
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 * Add a shrinker callback to be called from the vm.
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 */
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int register_shrinker(struct shrinker *shrinker)
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{
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	size_t size = sizeof(*shrinker->nr_deferred);

	if (shrinker->flags & SHRINKER_NUMA_AWARE)
		size *= nr_node_ids;

	shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
	if (!shrinker->nr_deferred)
		return -ENOMEM;

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	down_write(&shrinker_rwsem);
	list_add_tail(&shrinker->list, &shrinker_list);
	up_write(&shrinker_rwsem);
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	return 0;
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}
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EXPORT_SYMBOL(register_shrinker);
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/*
 * Remove one
 */
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void unregister_shrinker(struct shrinker *shrinker)
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{
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	if (!shrinker->nr_deferred)
		return;
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	down_write(&shrinker_rwsem);
	list_del(&shrinker->list);
	up_write(&shrinker_rwsem);
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	kfree(shrinker->nr_deferred);
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	shrinker->nr_deferred = NULL;
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}
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EXPORT_SYMBOL(unregister_shrinker);
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#define SHRINK_BATCH 128
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static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
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				    struct shrinker *shrinker, int priority)
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{
	unsigned long freed = 0;
	unsigned long long delta;
	long total_scan;
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	long freeable;
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	long nr;
	long new_nr;
	int nid = shrinkctl->nid;
	long batch_size = shrinker->batch ? shrinker->batch
					  : SHRINK_BATCH;
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	long scanned = 0, next_deferred;
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	freeable = shrinker->count_objects(shrinker, shrinkctl);
	if (freeable == 0)
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		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;
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	delta = freeable >> priority;
	delta *= 4;
	do_div(delta, shrinker->seeks);
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	total_scan += delta;
	if (total_scan < 0) {
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		pr_err("shrink_slab: %pF negative objects to delete nr=%ld\n",
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		       shrinker->scan_objects, total_scan);
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		total_scan = freeable;
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		next_deferred = nr;
	} else
		next_deferred = total_scan;
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	/*
	 * 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 >>>
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	 * freeable. This is bad for sustaining a working set in
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	 * memory.
	 *
	 * Hence only allow the shrinker to scan the entire cache when
	 * a large delta change is calculated directly.
	 */
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	if (delta < freeable / 4)
		total_scan = min(total_scan, freeable / 2);
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	/*
	 * Avoid risking looping forever due to too large nr value:
	 * never try to free more than twice the estimate number of
	 * freeable entries.
	 */
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	if (total_scan > freeable * 2)
		total_scan = freeable * 2;
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	trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
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				   freeable, delta, total_scan, priority);
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	/*
	 * 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
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	 * than the total number of objects on slab (freeable), we must be
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	 * scanning at high prio and therefore should try to reclaim as much as
	 * possible.
	 */
	while (total_scan >= batch_size ||
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	       total_scan >= freeable) {
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		unsigned long ret;
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		unsigned long nr_to_scan = min(batch_size, total_scan);
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		shrinkctl->nr_to_scan = nr_to_scan;
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		shrinkctl->nr_scanned = nr_to_scan;
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		ret = shrinker->scan_objects(shrinker, shrinkctl);
		if (ret == SHRINK_STOP)
			break;
		freed += ret;
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		count_vm_events(SLABS_SCANNED, shrinkctl->nr_scanned);
		total_scan -= shrinkctl->nr_scanned;
		scanned += shrinkctl->nr_scanned;
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		cond_resched();
	}

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	if (next_deferred >= scanned)
		next_deferred -= scanned;
	else
		next_deferred = 0;
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	/*
	 * 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.
	 */
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	if (next_deferred > 0)
		new_nr = atomic_long_add_return(next_deferred,
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						&shrinker->nr_deferred[nid]);
	else
		new_nr = atomic_long_read(&shrinker->nr_deferred[nid]);

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	trace_mm_shrink_slab_end(shrinker, nid, freed, nr, new_nr, total_scan);
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	return freed;
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}

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/**
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 * shrink_slab - shrink slab caches
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 * @gfp_mask: allocation context
 * @nid: node whose slab caches to target
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 * @memcg: memory cgroup whose slab caches to target
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 * @priority: the reclaim priority
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 *
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 * Call the shrink functions to age shrinkable caches.
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 *
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 * @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set,
 * unaware shrinkers will receive a node id of 0 instead.
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 *
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 * @memcg specifies the memory cgroup to target. If it is not NULL,
 * only shrinkers with SHRINKER_MEMCG_AWARE set will be called to scan
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 * objects from the memory cgroup specified. Otherwise, only unaware
 * shrinkers are called.
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 *
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 * @priority is sc->priority, we take the number of objects and >> by priority
 * in order to get the scan target.
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 *
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 * Returns the number of reclaimed slab objects.
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 */
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static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
				 struct mem_cgroup *memcg,
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				 int priority)
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{
	struct shrinker *shrinker;
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	unsigned long freed = 0;
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	if (memcg && (!memcg_kmem_enabled() || !mem_cgroup_online(memcg)))
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		return 0;

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	if (!down_read_trylock(&shrinker_rwsem)) {
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		/*
		 * 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;
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		goto out;
	}
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	list_for_each_entry(shrinker, &shrinker_list, list) {
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		struct shrink_control sc = {
			.gfp_mask = gfp_mask,
			.nid = nid,
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			.memcg = memcg,
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		};
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		/*
		 * If kernel memory accounting is disabled, we ignore
		 * SHRINKER_MEMCG_AWARE flag and call all shrinkers
		 * passing NULL for memcg.
		 */
		if (memcg_kmem_enabled() &&
		    !!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE))
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			continue;

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		if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
			sc.nid = 0;
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		freed += do_shrink_slab(&sc, shrinker, priority);
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		/*
		 * Bail out if someone want to register a new shrinker to
		 * prevent the regsitration from being stalled for long periods
		 * by parallel ongoing shrinking.
		 */
		if (rwsem_is_contended(&shrinker_rwsem)) {
			freed = freed ? : 1;
			break;
		}
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	}
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	up_read(&shrinker_rwsem);
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out:
	cond_resched();
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	return freed;
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}

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void drop_slab_node(int nid)
{
	unsigned long freed;

	do {
		struct mem_cgroup *memcg = NULL;

		freed = 0;
		do {
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			freed += shrink_slab(GFP_KERNEL, nid, memcg, 0);
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		} 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);
}

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static inline int is_page_cache_freeable(struct page *page)
{
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	/*
	 * 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.
	 */
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	int radix_pins = PageTransHuge(page) && PageSwapCache(page) ?
		HPAGE_PMD_NR : 1;
	return page_count(page) - page_has_private(page) == 1 + radix_pins;
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}

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static int may_write_to_inode(struct inode *inode, struct scan_control *sc)
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{
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	if (current->flags & PF_SWAPWRITE)
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		return 1;
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	if (!inode_write_congested(inode))
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		return 1;
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	if (inode_to_bdi(inode) == current->backing_dev_info)
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		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)
{
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	lock_page(page);
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	if (page_mapping(page) == mapping)
		mapping_set_error(mapping, error);
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	unlock_page(page);
}

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/* 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;

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/*
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 * pageout is called by shrink_page_list() for each dirty page.
 * Calls ->writepage().
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 */
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static pageout_t pageout(struct page *page, struct address_space *mapping,
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			 struct scan_control *sc)
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{
	/*
	 * 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.
	 *
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	 * If this process is currently in __generic_file_write_iter() against
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586 587 588 589 590 591 592 593 594 595 596 597 598 599 600
	 * 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.
		 */
601
		if (page_has_private(page)) {
L
Linus Torvalds 已提交
602 603
			if (try_to_free_buffers(page)) {
				ClearPageDirty(page);
604
				pr_info("%s: orphaned page\n", __func__);
L
Linus Torvalds 已提交
605 606 607 608 609 610 611
				return PAGE_CLEAN;
			}
		}
		return PAGE_KEEP;
	}
	if (mapping->a_ops->writepage == NULL)
		return PAGE_ACTIVATE;
612
	if (!may_write_to_inode(mapping->host, sc))
L
Linus Torvalds 已提交
613 614 615 616 617 618 619
		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,
620 621
			.range_start = 0,
			.range_end = LLONG_MAX,
L
Linus Torvalds 已提交
622 623 624 625 626 627 628
			.for_reclaim = 1,
		};

		SetPageReclaim(page);
		res = mapping->a_ops->writepage(page, &wbc);
		if (res < 0)
			handle_write_error(mapping, page, res);
629
		if (res == AOP_WRITEPAGE_ACTIVATE) {
L
Linus Torvalds 已提交
630 631 632
			ClearPageReclaim(page);
			return PAGE_ACTIVATE;
		}
633

L
Linus Torvalds 已提交
634 635 636 637
		if (!PageWriteback(page)) {
			/* synchronous write or broken a_ops? */
			ClearPageReclaim(page);
		}
638
		trace_mm_vmscan_writepage(page);
639
		inc_node_page_state(page, NR_VMSCAN_WRITE);
L
Linus Torvalds 已提交
640 641 642 643 644 645
		return PAGE_SUCCESS;
	}

	return PAGE_CLEAN;
}

646
/*
N
Nick Piggin 已提交
647 648
 * Same as remove_mapping, but if the page is removed from the mapping, it
 * gets returned with a refcount of 0.
649
 */
650 651
static int __remove_mapping(struct address_space *mapping, struct page *page,
			    bool reclaimed)
652
{
653
	unsigned long flags;
654
	int refcount;
655

656 657
	BUG_ON(!PageLocked(page));
	BUG_ON(mapping != page_mapping(page));
658

659
	spin_lock_irqsave(&mapping->tree_lock, flags);
660
	/*
N
Nick Piggin 已提交
661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679
	 * 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
680
	 * load is not satisfied before that of page->_refcount.
N
Nick Piggin 已提交
681 682 683
	 *
	 * Note that if SetPageDirty is always performed via set_page_dirty,
	 * and thus under tree_lock, then this ordering is not required.
684
	 */
685 686 687 688 689
	if (unlikely(PageTransHuge(page)) && PageSwapCache(page))
		refcount = 1 + HPAGE_PMD_NR;
	else
		refcount = 2;
	if (!page_ref_freeze(page, refcount))
690
		goto cannot_free;
N
Nick Piggin 已提交
691 692
	/* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
	if (unlikely(PageDirty(page))) {
693
		page_ref_unfreeze(page, refcount);
694
		goto cannot_free;
N
Nick Piggin 已提交
695
	}
696 697 698

	if (PageSwapCache(page)) {
		swp_entry_t swap = { .val = page_private(page) };
699
		mem_cgroup_swapout(page, swap);
700
		__delete_from_swap_cache(page);
701
		spin_unlock_irqrestore(&mapping->tree_lock, flags);
702
		put_swap_page(page, swap);
N
Nick Piggin 已提交
703
	} else {
704
		void (*freepage)(struct page *);
705
		void *shadow = NULL;
706 707

		freepage = mapping->a_ops->freepage;
708 709 710 711 712 713 714 715 716
		/*
		 * 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.
717 718 719 720 721 722
		 *
		 * We also don't store shadows for DAX mappings because the
		 * only page cache pages found in these are zero pages
		 * covering holes, and because we don't want to mix DAX
		 * exceptional entries and shadow exceptional entries in the
		 * same page_tree.
723 724
		 */
		if (reclaimed && page_is_file_cache(page) &&
725
		    !mapping_exiting(mapping) && !dax_mapping(mapping))
726
			shadow = workingset_eviction(mapping, page);
J
Johannes Weiner 已提交
727
		__delete_from_page_cache(page, shadow);
728
		spin_unlock_irqrestore(&mapping->tree_lock, flags);
729 730 731

		if (freepage != NULL)
			freepage(page);
732 733 734 735 736
	}

	return 1;

cannot_free:
737
	spin_unlock_irqrestore(&mapping->tree_lock, flags);
738 739 740
	return 0;
}

N
Nick Piggin 已提交
741 742 743 744 745 746 747 748
/*
 * 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)
{
749
	if (__remove_mapping(mapping, page, false)) {
N
Nick Piggin 已提交
750 751 752 753 754
		/*
		 * Unfreezing the refcount with 1 rather than 2 effectively
		 * drops the pagecache ref for us without requiring another
		 * atomic operation.
		 */
755
		page_ref_unfreeze(page, 1);
N
Nick Piggin 已提交
756 757 758 759 760
		return 1;
	}
	return 0;
}

L
Lee Schermerhorn 已提交
761 762 763 764 765 766 767 768 769 770 771
/**
 * 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)
{
772
	bool is_unevictable;
773
	int was_unevictable = PageUnevictable(page);
L
Lee Schermerhorn 已提交
774

775
	VM_BUG_ON_PAGE(PageLRU(page), page);
L
Lee Schermerhorn 已提交
776 777 778 779

redo:
	ClearPageUnevictable(page);

780
	if (page_evictable(page)) {
L
Lee Schermerhorn 已提交
781 782 783 784 785 786
		/*
		 * 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.
		 */
787
		is_unevictable = false;
788
		lru_cache_add(page);
L
Lee Schermerhorn 已提交
789 790 791 792 793
	} else {
		/*
		 * Put unevictable pages directly on zone's unevictable
		 * list.
		 */
794
		is_unevictable = true;
L
Lee Schermerhorn 已提交
795
		add_page_to_unevictable_list(page);
796
		/*
797 798 799
		 * 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
800
		 * isolation/check_move_unevictable_pages,
801
		 * we see PG_mlocked/AS_UNEVICTABLE cleared below and move
802 803
		 * the page back to the evictable list.
		 *
804
		 * The other side is TestClearPageMlocked() or shmem_lock().
805 806
		 */
		smp_mb();
L
Lee Schermerhorn 已提交
807 808 809 810 811 812 813
	}

	/*
	 * 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.
	 */
814
	if (is_unevictable && page_evictable(page)) {
L
Lee Schermerhorn 已提交
815 816 817 818 819 820 821 822 823 824
		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.
		 */
	}

825
	if (was_unevictable && !is_unevictable)
826
		count_vm_event(UNEVICTABLE_PGRESCUED);
827
	else if (!was_unevictable && is_unevictable)
828 829
		count_vm_event(UNEVICTABLE_PGCULLED);

L
Lee Schermerhorn 已提交
830 831 832
	put_page(page);		/* drop ref from isolate */
}

833 834 835
enum page_references {
	PAGEREF_RECLAIM,
	PAGEREF_RECLAIM_CLEAN,
836
	PAGEREF_KEEP,
837 838 839 840 841 842
	PAGEREF_ACTIVATE,
};

static enum page_references page_check_references(struct page *page,
						  struct scan_control *sc)
{
843
	int referenced_ptes, referenced_page;
844 845
	unsigned long vm_flags;

846 847
	referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
					  &vm_flags);
848
	referenced_page = TestClearPageReferenced(page);
849 850 851 852 853 854 855 856

	/*
	 * 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;

857
	if (referenced_ptes) {
858
		if (PageSwapBacked(page))
859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875
			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);

876
		if (referenced_page || referenced_ptes > 1)
877 878
			return PAGEREF_ACTIVATE;

879 880 881 882 883 884
		/*
		 * Activate file-backed executable pages after first usage.
		 */
		if (vm_flags & VM_EXEC)
			return PAGEREF_ACTIVATE;

885 886
		return PAGEREF_KEEP;
	}
887 888

	/* Reclaim if clean, defer dirty pages to writeback */
889
	if (referenced_page && !PageSwapBacked(page))
890 891 892
		return PAGEREF_RECLAIM_CLEAN;

	return PAGEREF_RECLAIM;
893 894
}

895 896 897 898
/* Check if a page is dirty or under writeback */
static void page_check_dirty_writeback(struct page *page,
				       bool *dirty, bool *writeback)
{
899 900
	struct address_space *mapping;

901 902 903 904
	/*
	 * Anonymous pages are not handled by flushers and must be written
	 * from reclaim context. Do not stall reclaim based on them
	 */
S
Shaohua Li 已提交
905 906
	if (!page_is_file_cache(page) ||
	    (PageAnon(page) && !PageSwapBacked(page))) {
907 908 909 910 911 912 913 914
		*dirty = false;
		*writeback = false;
		return;
	}

	/* By default assume that the page flags are accurate */
	*dirty = PageDirty(page);
	*writeback = PageWriteback(page);
915 916 917 918 919 920 921 922

	/* 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);
923 924
}

925 926 927 928 929 930
struct reclaim_stat {
	unsigned nr_dirty;
	unsigned nr_unqueued_dirty;
	unsigned nr_congested;
	unsigned nr_writeback;
	unsigned nr_immediate;
931 932 933
	unsigned nr_activate;
	unsigned nr_ref_keep;
	unsigned nr_unmap_fail;
934 935
};

L
Linus Torvalds 已提交
936
/*
A
Andrew Morton 已提交
937
 * shrink_page_list() returns the number of reclaimed pages
L
Linus Torvalds 已提交
938
 */
A
Andrew Morton 已提交
939
static unsigned long shrink_page_list(struct list_head *page_list,
M
Mel Gorman 已提交
940
				      struct pglist_data *pgdat,
941
				      struct scan_control *sc,
942
				      enum ttu_flags ttu_flags,
943
				      struct reclaim_stat *stat,
944
				      bool force_reclaim)
L
Linus Torvalds 已提交
945 946
{
	LIST_HEAD(ret_pages);
947
	LIST_HEAD(free_pages);
L
Linus Torvalds 已提交
948
	int pgactivate = 0;
949 950 951 952 953 954
	unsigned nr_unqueued_dirty = 0;
	unsigned nr_dirty = 0;
	unsigned nr_congested = 0;
	unsigned nr_reclaimed = 0;
	unsigned nr_writeback = 0;
	unsigned nr_immediate = 0;
955 956
	unsigned nr_ref_keep = 0;
	unsigned nr_unmap_fail = 0;
L
Linus Torvalds 已提交
957 958 959 960 961 962 963

	cond_resched();

	while (!list_empty(page_list)) {
		struct address_space *mapping;
		struct page *page;
		int may_enter_fs;
964
		enum page_references references = PAGEREF_RECLAIM_CLEAN;
965
		bool dirty, writeback;
L
Linus Torvalds 已提交
966 967 968 969 970 971

		cond_resched();

		page = lru_to_page(page_list);
		list_del(&page->lru);

N
Nick Piggin 已提交
972
		if (!trylock_page(page))
L
Linus Torvalds 已提交
973 974
			goto keep;

975
		VM_BUG_ON_PAGE(PageActive(page), page);
L
Linus Torvalds 已提交
976 977

		sc->nr_scanned++;
978

979
		if (unlikely(!page_evictable(page)))
M
Minchan Kim 已提交
980
			goto activate_locked;
L
Lee Schermerhorn 已提交
981

982
		if (!sc->may_unmap && page_mapped(page))
983 984
			goto keep_locked;

L
Linus Torvalds 已提交
985
		/* Double the slab pressure for mapped and swapcache pages */
S
Shaohua Li 已提交
986 987
		if ((page_mapped(page) || PageSwapCache(page)) &&
		    !(PageAnon(page) && !PageSwapBacked(page)))
L
Linus Torvalds 已提交
988 989
			sc->nr_scanned++;

990 991 992
		may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
			(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));

993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005
		/*
		 * 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++;

1006 1007 1008 1009 1010 1011
		/*
		 * 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.
		 */
1012
		mapping = page_mapping(page);
1013
		if (((dirty || writeback) && mapping &&
1014
		     inode_write_congested(mapping->host)) ||
1015
		    (writeback && PageReclaim(page)))
1016 1017
			nr_congested++;

1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028
		/*
		 * 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
1029 1030
		 *    note that the LRU is being scanned too quickly and the
		 *    caller can stall after page list has been processed.
1031
		 *
1032
		 * 2) Global or new memcg reclaim encounters a page that is
1033 1034 1035
		 *    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
1036
		 *    reclaim and continue scanning.
1037
		 *
1038 1039
		 *    Require may_enter_fs because we would wait on fs, which
		 *    may not have submitted IO yet. And the loop driver might
1040 1041 1042 1043 1044
		 *    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.
		 *
1045
		 * 3) Legacy memcg encounters a page that is already marked
1046 1047 1048 1049
		 *    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.
1050 1051 1052 1053 1054 1055 1056 1057 1058
		 *
		 * In cases 1) and 2) we activate the pages to get them out of
		 * the way while we continue scanning for clean pages on the
		 * inactive list and refilling from the active list. The
		 * observation here is that waiting for disk writes is more
		 * expensive than potentially causing reloads down the line.
		 * Since they're marked for immediate reclaim, they won't put
		 * memory pressure on the cache working set any longer than it
		 * takes to write them to disk.
1059
		 */
1060
		if (PageWriteback(page)) {
1061 1062 1063
			/* Case 1 above */
			if (current_is_kswapd() &&
			    PageReclaim(page) &&
M
Mel Gorman 已提交
1064
			    test_bit(PGDAT_WRITEBACK, &pgdat->flags)) {
1065
				nr_immediate++;
1066
				goto activate_locked;
1067 1068

			/* Case 2 above */
1069
			} else if (sane_reclaim(sc) ||
1070
			    !PageReclaim(page) || !may_enter_fs) {
1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082
				/*
				 * 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);
1083
				nr_writeback++;
1084
				goto activate_locked;
1085 1086 1087

			/* Case 3 above */
			} else {
1088
				unlock_page(page);
1089
				wait_on_page_writeback(page);
1090 1091 1092
				/* then go back and try same page again */
				list_add_tail(&page->lru, page_list);
				continue;
1093
			}
1094
		}
L
Linus Torvalds 已提交
1095

1096 1097 1098
		if (!force_reclaim)
			references = page_check_references(page, sc);

1099 1100
		switch (references) {
		case PAGEREF_ACTIVATE:
L
Linus Torvalds 已提交
1101
			goto activate_locked;
1102
		case PAGEREF_KEEP:
1103
			nr_ref_keep++;
1104
			goto keep_locked;
1105 1106 1107 1108
		case PAGEREF_RECLAIM:
		case PAGEREF_RECLAIM_CLEAN:
			; /* try to reclaim the page below */
		}
L
Linus Torvalds 已提交
1109 1110 1111 1112

		/*
		 * Anonymous process memory has backing store?
		 * Try to allocate it some swap space here.
S
Shaohua Li 已提交
1113
		 * Lazyfree page could be freed directly
L
Linus Torvalds 已提交
1114
		 */
1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139
		if (PageAnon(page) && PageSwapBacked(page)) {
			if (!PageSwapCache(page)) {
				if (!(sc->gfp_mask & __GFP_IO))
					goto keep_locked;
				if (PageTransHuge(page)) {
					/* cannot split THP, skip it */
					if (!can_split_huge_page(page, NULL))
						goto activate_locked;
					/*
					 * Split pages without a PMD map right
					 * away. Chances are some or all of the
					 * tail pages can be freed without IO.
					 */
					if (!compound_mapcount(page) &&
					    split_huge_page_to_list(page,
								    page_list))
						goto activate_locked;
				}
				if (!add_to_swap(page)) {
					if (!PageTransHuge(page))
						goto activate_locked;
					/* Fallback to swap normal pages */
					if (split_huge_page_to_list(page,
								    page_list))
						goto activate_locked;
1140 1141 1142
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
					count_vm_event(THP_SWPOUT_FALLBACK);
#endif
1143 1144 1145
					if (!add_to_swap(page))
						goto activate_locked;
				}
1146

1147
				may_enter_fs = 1;
L
Linus Torvalds 已提交
1148

1149 1150 1151
				/* Adding to swap updated mapping */
				mapping = page_mapping(page);
			}
1152 1153 1154 1155
		} else if (unlikely(PageTransHuge(page))) {
			/* Split file THP */
			if (split_huge_page_to_list(page, page_list))
				goto keep_locked;
1156
		}
L
Linus Torvalds 已提交
1157 1158 1159 1160 1161

		/*
		 * The page is mapped into the page tables of one or more
		 * processes. Try to unmap it here.
		 */
S
Shaohua Li 已提交
1162
		if (page_mapped(page)) {
1163 1164 1165 1166 1167
			enum ttu_flags flags = ttu_flags | TTU_BATCH_FLUSH;

			if (unlikely(PageTransHuge(page)))
				flags |= TTU_SPLIT_HUGE_PMD;
			if (!try_to_unmap(page, flags)) {
1168
				nr_unmap_fail++;
L
Linus Torvalds 已提交
1169 1170 1171 1172 1173
				goto activate_locked;
			}
		}

		if (PageDirty(page)) {
1174
			/*
1175 1176 1177 1178 1179 1180 1181 1182
			 * Only kswapd can writeback filesystem pages
			 * to avoid risk of stack overflow. But avoid
			 * injecting inefficient single-page IO into
			 * flusher writeback as much as possible: only
			 * write pages when we've encountered many
			 * dirty pages, and when we've already scanned
			 * the rest of the LRU for clean pages and see
			 * the same dirty pages again (PageReclaim).
1183
			 */
1184
			if (page_is_file_cache(page) &&
1185 1186
			    (!current_is_kswapd() || !PageReclaim(page) ||
			     !test_bit(PGDAT_DIRTY, &pgdat->flags))) {
1187 1188 1189 1190 1191 1192
				/*
				 * Immediately reclaim when written back.
				 * Similar in principal to deactivate_page()
				 * except we already have the page isolated
				 * and know it's dirty
				 */
1193
				inc_node_page_state(page, NR_VMSCAN_IMMEDIATE);
1194 1195
				SetPageReclaim(page);

1196
				goto activate_locked;
1197 1198
			}

1199
			if (references == PAGEREF_RECLAIM_CLEAN)
L
Linus Torvalds 已提交
1200
				goto keep_locked;
1201
			if (!may_enter_fs)
L
Linus Torvalds 已提交
1202
				goto keep_locked;
1203
			if (!sc->may_writepage)
L
Linus Torvalds 已提交
1204 1205
				goto keep_locked;

1206 1207 1208 1209 1210 1211
			/*
			 * 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();
1212
			switch (pageout(page, mapping, sc)) {
L
Linus Torvalds 已提交
1213 1214 1215 1216 1217
			case PAGE_KEEP:
				goto keep_locked;
			case PAGE_ACTIVATE:
				goto activate_locked;
			case PAGE_SUCCESS:
1218
				if (PageWriteback(page))
1219
					goto keep;
1220
				if (PageDirty(page))
L
Linus Torvalds 已提交
1221
					goto keep;
1222

L
Linus Torvalds 已提交
1223 1224 1225 1226
				/*
				 * A synchronous write - probably a ramdisk.  Go
				 * ahead and try to reclaim the page.
				 */
N
Nick Piggin 已提交
1227
				if (!trylock_page(page))
L
Linus Torvalds 已提交
1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246
					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
L
Lee Schermerhorn 已提交
1247
		 * will do this, as well as the blockdev mapping.
L
Linus Torvalds 已提交
1248 1249 1250 1251 1252 1253 1254 1255 1256 1257
		 * 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.
		 */
1258
		if (page_has_private(page)) {
L
Linus Torvalds 已提交
1259 1260
			if (!try_to_release_page(page, sc->gfp_mask))
				goto activate_locked;
N
Nick Piggin 已提交
1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276
			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;
				}
			}
L
Linus Torvalds 已提交
1277 1278
		}

S
Shaohua Li 已提交
1279 1280 1281 1282 1283 1284 1285 1286
		if (PageAnon(page) && !PageSwapBacked(page)) {
			/* follow __remove_mapping for reference */
			if (!page_ref_freeze(page, 1))
				goto keep_locked;
			if (PageDirty(page)) {
				page_ref_unfreeze(page, 1);
				goto keep_locked;
			}
L
Linus Torvalds 已提交
1287

S
Shaohua Li 已提交
1288
			count_vm_event(PGLAZYFREED);
1289
			count_memcg_page_event(page, PGLAZYFREED);
S
Shaohua Li 已提交
1290 1291
		} else if (!mapping || !__remove_mapping(mapping, page, true))
			goto keep_locked;
N
Nick Piggin 已提交
1292 1293 1294 1295 1296 1297 1298
		/*
		 * 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.
		 */
1299
		__ClearPageLocked(page);
N
Nick Piggin 已提交
1300
free_it:
1301
		nr_reclaimed++;
1302 1303 1304 1305 1306

		/*
		 * Is there need to periodically free_page_list? It would
		 * appear not as the counts should be low
		 */
1307 1308 1309 1310 1311
		if (unlikely(PageTransHuge(page))) {
			mem_cgroup_uncharge(page);
			(*get_compound_page_dtor(page))(page);
		} else
			list_add(&page->lru, &free_pages);
L
Linus Torvalds 已提交
1312 1313 1314
		continue;

activate_locked:
1315
		/* Not a candidate for swapping, so reclaim swap space. */
M
Minchan Kim 已提交
1316 1317
		if (PageSwapCache(page) && (mem_cgroup_swap_full(page) ||
						PageMlocked(page)))
1318
			try_to_free_swap(page);
1319
		VM_BUG_ON_PAGE(PageActive(page), page);
M
Minchan Kim 已提交
1320 1321 1322
		if (!PageMlocked(page)) {
			SetPageActive(page);
			pgactivate++;
1323
			count_memcg_page_event(page, PGACTIVATE);
M
Minchan Kim 已提交
1324
		}
L
Linus Torvalds 已提交
1325 1326 1327 1328
keep_locked:
		unlock_page(page);
keep:
		list_add(&page->lru, &ret_pages);
1329
		VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page);
L
Linus Torvalds 已提交
1330
	}
1331

1332
	mem_cgroup_uncharge_list(&free_pages);
1333
	try_to_unmap_flush();
1334
	free_unref_page_list(&free_pages);
1335

L
Linus Torvalds 已提交
1336
	list_splice(&ret_pages, page_list);
1337
	count_vm_events(PGACTIVATE, pgactivate);
1338

1339 1340 1341 1342 1343 1344
	if (stat) {
		stat->nr_dirty = nr_dirty;
		stat->nr_congested = nr_congested;
		stat->nr_unqueued_dirty = nr_unqueued_dirty;
		stat->nr_writeback = nr_writeback;
		stat->nr_immediate = nr_immediate;
1345 1346 1347
		stat->nr_activate = pgactivate;
		stat->nr_ref_keep = nr_ref_keep;
		stat->nr_unmap_fail = nr_unmap_fail;
1348
	}
1349
	return nr_reclaimed;
L
Linus Torvalds 已提交
1350 1351
}

1352 1353 1354 1355 1356 1357 1358 1359
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,
	};
1360
	unsigned long ret;
1361 1362 1363 1364
	struct page *page, *next;
	LIST_HEAD(clean_pages);

	list_for_each_entry_safe(page, next, page_list, lru) {
1365
		if (page_is_file_cache(page) && !PageDirty(page) &&
1366
		    !__PageMovable(page)) {
1367 1368 1369 1370 1371
			ClearPageActive(page);
			list_move(&page->lru, &clean_pages);
		}
	}

M
Mel Gorman 已提交
1372
	ret = shrink_page_list(&clean_pages, zone->zone_pgdat, &sc,
S
Shaohua Li 已提交
1373
			TTU_IGNORE_ACCESS, NULL, true);
1374
	list_splice(&clean_pages, page_list);
M
Mel Gorman 已提交
1375
	mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE, -ret);
1376 1377 1378
	return ret;
}

A
Andy Whitcroft 已提交
1379 1380 1381 1382 1383 1384 1385 1386 1387 1388
/*
 * 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.
 */
1389
int __isolate_lru_page(struct page *page, isolate_mode_t mode)
A
Andy Whitcroft 已提交
1390 1391 1392 1393 1394 1395 1396
{
	int ret = -EINVAL;

	/* Only take pages on the LRU. */
	if (!PageLRU(page))
		return ret;

M
Minchan Kim 已提交
1397 1398
	/* Compaction should not handle unevictable pages but CMA can do so */
	if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
L
Lee Schermerhorn 已提交
1399 1400
		return ret;

A
Andy Whitcroft 已提交
1401
	ret = -EBUSY;
K
KAMEZAWA Hiroyuki 已提交
1402

1403 1404 1405 1406 1407 1408 1409 1410
	/*
	 * 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_ASYNC_MIGRATE is used to indicate that it only wants to pages
	 * that it is possible to migrate without blocking
	 */
1411
	if (mode & ISOLATE_ASYNC_MIGRATE) {
1412 1413 1414 1415 1416 1417
		/* All the caller can do on PageWriteback is block */
		if (PageWriteback(page))
			return ret;

		if (PageDirty(page)) {
			struct address_space *mapping;
1418
			bool migrate_dirty;
1419 1420 1421 1422

			/*
			 * Only pages without mappings or that have a
			 * ->migratepage callback are possible to migrate
1423 1424 1425 1426 1427
			 * without blocking. However, we can be racing with
			 * truncation so it's necessary to lock the page
			 * to stabilise the mapping as truncation holds
			 * the page lock until after the page is removed
			 * from the page cache.
1428
			 */
1429 1430 1431
			if (!trylock_page(page))
				return ret;

1432
			mapping = page_mapping(page);
1433 1434 1435
			migrate_dirty = mapping && mapping->a_ops->migratepage;
			unlock_page(page);
			if (!migrate_dirty)
1436 1437 1438
				return ret;
		}
	}
1439

1440 1441 1442
	if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
		return ret;

A
Andy Whitcroft 已提交
1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455
	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;
}

1456 1457 1458 1459 1460 1461

/*
 * Update LRU sizes after isolating pages. The LRU size updates must
 * be complete before mem_cgroup_update_lru_size due to a santity check.
 */
static __always_inline void update_lru_sizes(struct lruvec *lruvec,
1462
			enum lru_list lru, unsigned long *nr_zone_taken)
1463 1464 1465 1466 1467 1468 1469 1470 1471
{
	int zid;

	for (zid = 0; zid < MAX_NR_ZONES; zid++) {
		if (!nr_zone_taken[zid])
			continue;

		__update_lru_size(lruvec, lru, zid, -nr_zone_taken[zid]);
#ifdef CONFIG_MEMCG
1472
		mem_cgroup_update_lru_size(lruvec, lru, zid, -nr_zone_taken[zid]);
1473
#endif
1474 1475
	}

1476 1477
}

L
Linus Torvalds 已提交
1478
/*
1479
 * zone_lru_lock is heavily contended.  Some of the functions that
L
Linus Torvalds 已提交
1480 1481 1482 1483 1484 1485 1486 1487
 * 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.
 *
1488
 * @nr_to_scan:	The number of eligible pages to look through on the list.
1489
 * @lruvec:	The LRU vector to pull pages from.
L
Linus Torvalds 已提交
1490
 * @dst:	The temp list to put pages on to.
H
Hugh Dickins 已提交
1491
 * @nr_scanned:	The number of pages that were scanned.
1492
 * @sc:		The scan_control struct for this reclaim session
A
Andy Whitcroft 已提交
1493
 * @mode:	One of the LRU isolation modes
1494
 * @lru:	LRU list id for isolating
L
Linus Torvalds 已提交
1495 1496 1497
 *
 * returns how many pages were moved onto *@dst.
 */
1498
static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1499
		struct lruvec *lruvec, struct list_head *dst,
1500
		unsigned long *nr_scanned, struct scan_control *sc,
1501
		isolate_mode_t mode, enum lru_list lru)
L
Linus Torvalds 已提交
1502
{
H
Hugh Dickins 已提交
1503
	struct list_head *src = &lruvec->lists[lru];
1504
	unsigned long nr_taken = 0;
M
Mel Gorman 已提交
1505
	unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 };
1506
	unsigned long nr_skipped[MAX_NR_ZONES] = { 0, };
1507
	unsigned long skipped = 0;
1508
	unsigned long scan, total_scan, nr_pages;
1509
	LIST_HEAD(pages_skipped);
L
Linus Torvalds 已提交
1510

1511 1512 1513 1514
	scan = 0;
	for (total_scan = 0;
	     scan < nr_to_scan && nr_taken < nr_to_scan && !list_empty(src);
	     total_scan++) {
A
Andy Whitcroft 已提交
1515 1516
		struct page *page;

L
Linus Torvalds 已提交
1517 1518 1519
		page = lru_to_page(src);
		prefetchw_prev_lru_page(page, src, flags);

1520
		VM_BUG_ON_PAGE(!PageLRU(page), page);
N
Nick Piggin 已提交
1521

1522 1523
		if (page_zonenum(page) > sc->reclaim_idx) {
			list_move(&page->lru, &pages_skipped);
1524
			nr_skipped[page_zonenum(page)]++;
1525 1526 1527
			continue;
		}

1528 1529 1530 1531 1532 1533 1534
		/*
		 * Do not count skipped pages because that makes the function
		 * return with no isolated pages if the LRU mostly contains
		 * ineligible pages.  This causes the VM to not reclaim any
		 * pages, triggering a premature OOM.
		 */
		scan++;
1535
		switch (__isolate_lru_page(page, mode)) {
A
Andy Whitcroft 已提交
1536
		case 0:
M
Mel Gorman 已提交
1537 1538 1539
			nr_pages = hpage_nr_pages(page);
			nr_taken += nr_pages;
			nr_zone_taken[page_zonenum(page)] += nr_pages;
A
Andy Whitcroft 已提交
1540 1541 1542 1543 1544 1545 1546
			list_move(&page->lru, dst);
			break;

		case -EBUSY:
			/* else it is being freed elsewhere */
			list_move(&page->lru, src);
			continue;
1547

A
Andy Whitcroft 已提交
1548 1549 1550
		default:
			BUG();
		}
L
Linus Torvalds 已提交
1551 1552
	}

1553 1554 1555 1556 1557 1558 1559
	/*
	 * Splice any skipped pages to the start of the LRU list. Note that
	 * this disrupts the LRU order when reclaiming for lower zones but
	 * we cannot splice to the tail. If we did then the SWAP_CLUSTER_MAX
	 * scanning would soon rescan the same pages to skip and put the
	 * system at risk of premature OOM.
	 */
1560 1561 1562
	if (!list_empty(&pages_skipped)) {
		int zid;

1563
		list_splice(&pages_skipped, src);
1564 1565 1566 1567 1568
		for (zid = 0; zid < MAX_NR_ZONES; zid++) {
			if (!nr_skipped[zid])
				continue;

			__count_zid_vm_events(PGSCAN_SKIP, zid, nr_skipped[zid]);
1569
			skipped += nr_skipped[zid];
1570 1571
		}
	}
1572
	*nr_scanned = total_scan;
1573
	trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan,
1574
				    total_scan, skipped, nr_taken, mode, lru);
1575
	update_lru_sizes(lruvec, lru, nr_zone_taken);
L
Linus Torvalds 已提交
1576 1577 1578
	return nr_taken;
}

1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589
/**
 * 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
L
Lee Schermerhorn 已提交
1590 1591 1592
 * 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.
1593 1594 1595 1596 1597
 *
 * The vmstat statistic corresponding to the list on which the page was
 * found will be decremented.
 *
 * Restrictions:
1598
 *
1599 1600 1601 1602 1603 1604 1605 1606 1607 1608
 * (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;

1609
	VM_BUG_ON_PAGE(!page_count(page), page);
1610
	WARN_RATELIMIT(PageTail(page), "trying to isolate tail page");
1611

1612 1613
	if (PageLRU(page)) {
		struct zone *zone = page_zone(page);
1614
		struct lruvec *lruvec;
1615

1616
		spin_lock_irq(zone_lru_lock(zone));
M
Mel Gorman 已提交
1617
		lruvec = mem_cgroup_page_lruvec(page, zone->zone_pgdat);
1618
		if (PageLRU(page)) {
L
Lee Schermerhorn 已提交
1619
			int lru = page_lru(page);
1620
			get_page(page);
1621
			ClearPageLRU(page);
1622 1623
			del_page_from_lru_list(page, lruvec, lru);
			ret = 0;
1624
		}
1625
		spin_unlock_irq(zone_lru_lock(zone));
1626 1627 1628 1629
	}
	return ret;
}

1630
/*
F
Fengguang Wu 已提交
1631 1632 1633 1634 1635
 * 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.
1636
 */
M
Mel Gorman 已提交
1637
static int too_many_isolated(struct pglist_data *pgdat, int file,
1638 1639 1640 1641 1642 1643 1644
		struct scan_control *sc)
{
	unsigned long inactive, isolated;

	if (current_is_kswapd())
		return 0;

1645
	if (!sane_reclaim(sc))
1646 1647 1648
		return 0;

	if (file) {
M
Mel Gorman 已提交
1649 1650
		inactive = node_page_state(pgdat, NR_INACTIVE_FILE);
		isolated = node_page_state(pgdat, NR_ISOLATED_FILE);
1651
	} else {
M
Mel Gorman 已提交
1652 1653
		inactive = node_page_state(pgdat, NR_INACTIVE_ANON);
		isolated = node_page_state(pgdat, NR_ISOLATED_ANON);
1654 1655
	}

1656 1657 1658 1659 1660
	/*
	 * 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.
	 */
1661
	if ((sc->gfp_mask & (__GFP_IO | __GFP_FS)) == (__GFP_IO | __GFP_FS))
1662 1663
		inactive >>= 3;

1664 1665 1666
	return isolated > inactive;
}

1667
static noinline_for_stack void
H
Hugh Dickins 已提交
1668
putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
1669
{
1670
	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
M
Mel Gorman 已提交
1671
	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1672
	LIST_HEAD(pages_to_free);
1673 1674 1675 1676 1677

	/*
	 * Put back any unfreeable pages.
	 */
	while (!list_empty(page_list)) {
1678
		struct page *page = lru_to_page(page_list);
1679
		int lru;
1680

1681
		VM_BUG_ON_PAGE(PageLRU(page), page);
1682
		list_del(&page->lru);
1683
		if (unlikely(!page_evictable(page))) {
M
Mel Gorman 已提交
1684
			spin_unlock_irq(&pgdat->lru_lock);
1685
			putback_lru_page(page);
M
Mel Gorman 已提交
1686
			spin_lock_irq(&pgdat->lru_lock);
1687 1688
			continue;
		}
1689

M
Mel Gorman 已提交
1690
		lruvec = mem_cgroup_page_lruvec(page, pgdat);
1691

1692
		SetPageLRU(page);
1693
		lru = page_lru(page);
1694 1695
		add_page_to_lru_list(page, lruvec, lru);

1696 1697
		if (is_active_lru(lru)) {
			int file = is_file_lru(lru);
1698 1699
			int numpages = hpage_nr_pages(page);
			reclaim_stat->recent_rotated[file] += numpages;
1700
		}
1701 1702 1703
		if (put_page_testzero(page)) {
			__ClearPageLRU(page);
			__ClearPageActive(page);
1704
			del_page_from_lru_list(page, lruvec, lru);
1705 1706

			if (unlikely(PageCompound(page))) {
M
Mel Gorman 已提交
1707
				spin_unlock_irq(&pgdat->lru_lock);
1708
				mem_cgroup_uncharge(page);
1709
				(*get_compound_page_dtor(page))(page);
M
Mel Gorman 已提交
1710
				spin_lock_irq(&pgdat->lru_lock);
1711 1712
			} else
				list_add(&page->lru, &pages_to_free);
1713 1714 1715
		}
	}

1716 1717 1718 1719
	/*
	 * To save our caller's stack, now use input list for pages to free.
	 */
	list_splice(&pages_to_free, page_list);
1720 1721
}

1722 1723 1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734
/*
 * 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);
}

L
Linus Torvalds 已提交
1735
/*
1736
 * shrink_inactive_list() is a helper for shrink_node().  It returns the number
A
Andrew Morton 已提交
1737
 * of reclaimed pages
L
Linus Torvalds 已提交
1738
 */
1739
static noinline_for_stack unsigned long
1740
shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1741
		     struct scan_control *sc, enum lru_list lru)
L
Linus Torvalds 已提交
1742 1743
{
	LIST_HEAD(page_list);
1744
	unsigned long nr_scanned;
1745
	unsigned long nr_reclaimed = 0;
1746
	unsigned long nr_taken;
1747
	struct reclaim_stat stat = {};
1748
	isolate_mode_t isolate_mode = 0;
1749
	int file = is_file_lru(lru);
M
Mel Gorman 已提交
1750
	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1751
	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1752
	bool stalled = false;
1753

M
Mel Gorman 已提交
1754
	while (unlikely(too_many_isolated(pgdat, file, sc))) {
1755 1756 1757 1758 1759 1760
		if (stalled)
			return 0;

		/* wait a bit for the reclaimer. */
		msleep(100);
		stalled = true;
1761 1762 1763 1764 1765 1766

		/* We are about to die and free our memory. Return now. */
		if (fatal_signal_pending(current))
			return SWAP_CLUSTER_MAX;
	}

L
Linus Torvalds 已提交
1767
	lru_add_drain();
1768 1769

	if (!sc->may_unmap)
1770
		isolate_mode |= ISOLATE_UNMAPPED;
1771

M
Mel Gorman 已提交
1772
	spin_lock_irq(&pgdat->lru_lock);
1773

1774 1775
	nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
				     &nr_scanned, sc, isolate_mode, lru);
1776

M
Mel Gorman 已提交
1777
	__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
1778
	reclaim_stat->recent_scanned[file] += nr_taken;
1779

1780 1781
	if (current_is_kswapd()) {
		if (global_reclaim(sc))
M
Mel Gorman 已提交
1782
			__count_vm_events(PGSCAN_KSWAPD, nr_scanned);
1783 1784 1785 1786
		count_memcg_events(lruvec_memcg(lruvec), PGSCAN_KSWAPD,
				   nr_scanned);
	} else {
		if (global_reclaim(sc))
M
Mel Gorman 已提交
1787
			__count_vm_events(PGSCAN_DIRECT, nr_scanned);
1788 1789
		count_memcg_events(lruvec_memcg(lruvec), PGSCAN_DIRECT,
				   nr_scanned);
1790
	}
M
Mel Gorman 已提交
1791
	spin_unlock_irq(&pgdat->lru_lock);
1792

1793
	if (nr_taken == 0)
1794
		return 0;
A
Andy Whitcroft 已提交
1795

S
Shaohua Li 已提交
1796
	nr_reclaimed = shrink_page_list(&page_list, pgdat, sc, 0,
1797
				&stat, false);
1798

M
Mel Gorman 已提交
1799
	spin_lock_irq(&pgdat->lru_lock);
1800

1801 1802
	if (current_is_kswapd()) {
		if (global_reclaim(sc))
M
Mel Gorman 已提交
1803
			__count_vm_events(PGSTEAL_KSWAPD, nr_reclaimed);
1804 1805 1806 1807
		count_memcg_events(lruvec_memcg(lruvec), PGSTEAL_KSWAPD,
				   nr_reclaimed);
	} else {
		if (global_reclaim(sc))
M
Mel Gorman 已提交
1808
			__count_vm_events(PGSTEAL_DIRECT, nr_reclaimed);
1809 1810
		count_memcg_events(lruvec_memcg(lruvec), PGSTEAL_DIRECT,
				   nr_reclaimed);
Y
Ying Han 已提交
1811
	}
N
Nick Piggin 已提交
1812

1813
	putback_inactive_pages(lruvec, &page_list);
1814

M
Mel Gorman 已提交
1815
	__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
1816

M
Mel Gorman 已提交
1817
	spin_unlock_irq(&pgdat->lru_lock);
1818

1819
	mem_cgroup_uncharge_list(&page_list);
1820
	free_unref_page_list(&page_list);
1821

1822 1823 1824 1825 1826 1827 1828 1829 1830 1831
	/*
	 * 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.
	 *
1832 1833 1834
	 * 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.
1835
	 */
1836
	if (stat.nr_writeback && stat.nr_writeback == nr_taken)
M
Mel Gorman 已提交
1837
		set_bit(PGDAT_WRITEBACK, &pgdat->flags);
1838

1839
	/*
1840 1841
	 * Legacy memcg will stall in page writeback so avoid forcibly
	 * stalling here.
1842
	 */
1843
	if (sane_reclaim(sc)) {
1844 1845 1846 1847
		/*
		 * Tag a zone as congested if all the dirty pages scanned were
		 * backed by a congested BDI and wait_iff_congested will stall.
		 */
1848
		if (stat.nr_dirty && stat.nr_dirty == stat.nr_congested)
M
Mel Gorman 已提交
1849
			set_bit(PGDAT_CONGESTED, &pgdat->flags);
1850

1851 1852
		/*
		 * If dirty pages are scanned that are not queued for IO, it
1853 1854 1855 1856 1857 1858 1859 1860 1861
		 * implies that flushers are not doing their job. This can
		 * happen when memory pressure pushes dirty pages to the end of
		 * the LRU before the dirty limits are breached and the dirty
		 * data has expired. It can also happen when the proportion of
		 * dirty pages grows not through writes but through memory
		 * pressure reclaiming all the clean cache. And in some cases,
		 * the flushers simply cannot keep up with the allocation
		 * rate. Nudge the flusher threads in case they are asleep, but
		 * also allow kswapd to start writing pages during reclaim.
1862
		 */
1863
		if (stat.nr_unqueued_dirty == nr_taken) {
1864
			wakeup_flusher_threads(WB_REASON_VMSCAN);
M
Mel Gorman 已提交
1865
			set_bit(PGDAT_DIRTY, &pgdat->flags);
1866
		}
1867 1868

		/*
1869 1870 1871
		 * 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
1872 1873
		 * they are written so also forcibly stall.
		 */
1874
		if (stat.nr_immediate && current_may_throttle())
1875
			congestion_wait(BLK_RW_ASYNC, HZ/10);
1876
	}
1877

1878 1879 1880 1881 1882
	/*
	 * 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.
	 */
1883 1884
	if (!sc->hibernation_mode && !current_is_kswapd() &&
	    current_may_throttle())
M
Mel Gorman 已提交
1885
		wait_iff_congested(pgdat, BLK_RW_ASYNC, HZ/10);
1886

M
Mel Gorman 已提交
1887 1888
	trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,
			nr_scanned, nr_reclaimed,
1889 1890 1891 1892
			stat.nr_dirty,  stat.nr_writeback,
			stat.nr_congested, stat.nr_immediate,
			stat.nr_activate, stat.nr_ref_keep,
			stat.nr_unmap_fail,
1893
			sc->priority, file);
1894
	return nr_reclaimed;
L
Linus Torvalds 已提交
1895 1896 1897 1898 1899 1900 1901 1902 1903
}

/*
 * 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
1904
 * appropriate to hold zone_lru_lock across the whole operation.  But if
L
Linus Torvalds 已提交
1905
 * the pages are mapped, the processing is slow (page_referenced()) so we
1906
 * should drop zone_lru_lock around each page.  It's impossible to balance
L
Linus Torvalds 已提交
1907 1908 1909 1910
 * 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.
 *
1911
 * The downside is that we have to touch page->_refcount against each page.
L
Linus Torvalds 已提交
1912
 * But we had to alter page->flags anyway.
1913 1914
 *
 * Returns the number of pages moved to the given lru.
L
Linus Torvalds 已提交
1915
 */
1916

1917
static unsigned move_active_pages_to_lru(struct lruvec *lruvec,
1918
				     struct list_head *list,
1919
				     struct list_head *pages_to_free,
1920 1921
				     enum lru_list lru)
{
M
Mel Gorman 已提交
1922
	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1923
	struct page *page;
1924
	int nr_pages;
1925
	int nr_moved = 0;
1926 1927 1928

	while (!list_empty(list)) {
		page = lru_to_page(list);
M
Mel Gorman 已提交
1929
		lruvec = mem_cgroup_page_lruvec(page, pgdat);
1930

1931
		VM_BUG_ON_PAGE(PageLRU(page), page);
1932 1933
		SetPageLRU(page);

1934
		nr_pages = hpage_nr_pages(page);
M
Mel Gorman 已提交
1935
		update_lru_size(lruvec, lru, page_zonenum(page), nr_pages);
1936
		list_move(&page->lru, &lruvec->lists[lru]);
1937

1938 1939 1940
		if (put_page_testzero(page)) {
			__ClearPageLRU(page);
			__ClearPageActive(page);
1941
			del_page_from_lru_list(page, lruvec, lru);
1942 1943

			if (unlikely(PageCompound(page))) {
M
Mel Gorman 已提交
1944
				spin_unlock_irq(&pgdat->lru_lock);
1945
				mem_cgroup_uncharge(page);
1946
				(*get_compound_page_dtor(page))(page);
M
Mel Gorman 已提交
1947
				spin_lock_irq(&pgdat->lru_lock);
1948 1949
			} else
				list_add(&page->lru, pages_to_free);
1950 1951
		} else {
			nr_moved += nr_pages;
1952 1953
		}
	}
1954

1955
	if (!is_active_lru(lru)) {
1956
		__count_vm_events(PGDEACTIVATE, nr_moved);
1957 1958 1959
		count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE,
				   nr_moved);
	}
1960 1961

	return nr_moved;
1962
}
1963

H
Hugh Dickins 已提交
1964
static void shrink_active_list(unsigned long nr_to_scan,
1965
			       struct lruvec *lruvec,
1966
			       struct scan_control *sc,
1967
			       enum lru_list lru)
L
Linus Torvalds 已提交
1968
{
1969
	unsigned long nr_taken;
H
Hugh Dickins 已提交
1970
	unsigned long nr_scanned;
1971
	unsigned long vm_flags;
L
Linus Torvalds 已提交
1972
	LIST_HEAD(l_hold);	/* The pages which were snipped off */
1973
	LIST_HEAD(l_active);
1974
	LIST_HEAD(l_inactive);
L
Linus Torvalds 已提交
1975
	struct page *page;
1976
	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1977 1978
	unsigned nr_deactivate, nr_activate;
	unsigned nr_rotated = 0;
1979
	isolate_mode_t isolate_mode = 0;
1980
	int file = is_file_lru(lru);
M
Mel Gorman 已提交
1981
	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
L
Linus Torvalds 已提交
1982 1983

	lru_add_drain();
1984 1985

	if (!sc->may_unmap)
1986
		isolate_mode |= ISOLATE_UNMAPPED;
1987

M
Mel Gorman 已提交
1988
	spin_lock_irq(&pgdat->lru_lock);
1989

1990 1991
	nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
				     &nr_scanned, sc, isolate_mode, lru);
1992

M
Mel Gorman 已提交
1993
	__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
1994
	reclaim_stat->recent_scanned[file] += nr_taken;
1995

M
Mel Gorman 已提交
1996
	__count_vm_events(PGREFILL, nr_scanned);
1997
	count_memcg_events(lruvec_memcg(lruvec), PGREFILL, nr_scanned);
1998

M
Mel Gorman 已提交
1999
	spin_unlock_irq(&pgdat->lru_lock);
L
Linus Torvalds 已提交
2000 2001 2002 2003 2004

	while (!list_empty(&l_hold)) {
		cond_resched();
		page = lru_to_page(&l_hold);
		list_del(&page->lru);
2005

2006
		if (unlikely(!page_evictable(page))) {
L
Lee Schermerhorn 已提交
2007 2008 2009 2010
			putback_lru_page(page);
			continue;
		}

2011 2012 2013 2014 2015 2016 2017 2018
		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);
			}
		}

2019 2020
		if (page_referenced(page, 0, sc->target_mem_cgroup,
				    &vm_flags)) {
2021
			nr_rotated += hpage_nr_pages(page);
2022 2023 2024 2025 2026 2027 2028 2029 2030
			/*
			 * 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.
			 */
2031
			if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
2032 2033 2034 2035
				list_add(&page->lru, &l_active);
				continue;
			}
		}
2036

2037
		ClearPageActive(page);	/* we are de-activating */
L
Linus Torvalds 已提交
2038 2039 2040
		list_add(&page->lru, &l_inactive);
	}

2041
	/*
2042
	 * Move pages back to the lru list.
2043
	 */
M
Mel Gorman 已提交
2044
	spin_lock_irq(&pgdat->lru_lock);
2045
	/*
2046 2047 2048
	 * 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
2049
	 * get_scan_count.
2050
	 */
2051
	reclaim_stat->recent_rotated[file] += nr_rotated;
2052

2053 2054
	nr_activate = move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
	nr_deactivate = move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
M
Mel Gorman 已提交
2055 2056
	__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
	spin_unlock_irq(&pgdat->lru_lock);
2057

2058
	mem_cgroup_uncharge_list(&l_hold);
2059
	free_unref_page_list(&l_hold);
2060 2061
	trace_mm_vmscan_lru_shrink_active(pgdat->node_id, nr_taken, nr_activate,
			nr_deactivate, nr_rotated, sc->priority, file);
L
Linus Torvalds 已提交
2062 2063
}

2064 2065 2066
/*
 * The inactive anon list should be small enough that the VM never has
 * to do too much work.
2067
 *
2068 2069 2070
 * The inactive file list should be small enough to leave most memory
 * to the established workingset on the scan-resistant active list,
 * but large enough to avoid thrashing the aggregate readahead window.
2071
 *
2072 2073
 * Both inactive lists should also be large enough that each inactive
 * page has a chance to be referenced again before it is reclaimed.
2074
 *
2075 2076
 * If that fails and refaulting is observed, the inactive list grows.
 *
2077
 * The inactive_ratio is the target ratio of ACTIVE to INACTIVE pages
2078
 * on this LRU, maintained by the pageout code. An inactive_ratio
2079
 * of 3 means 3:1 or 25% of the pages are kept on the inactive list.
2080
 *
2081 2082 2083 2084 2085 2086 2087 2088 2089 2090
 * total     target    max
 * memory    ratio     inactive
 * -------------------------------------
 *   10MB       1         5MB
 *  100MB       1        50MB
 *    1GB       3       250MB
 *   10GB      10       0.9GB
 *  100GB      31         3GB
 *    1TB     101        10GB
 *   10TB     320        32GB
2091
 */
2092
static bool inactive_list_is_low(struct lruvec *lruvec, bool file,
2093 2094
				 struct mem_cgroup *memcg,
				 struct scan_control *sc, bool actual_reclaim)
2095
{
2096
	enum lru_list active_lru = file * LRU_FILE + LRU_ACTIVE;
2097 2098 2099 2100 2101
	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
	enum lru_list inactive_lru = file * LRU_FILE;
	unsigned long inactive, active;
	unsigned long inactive_ratio;
	unsigned long refaults;
2102
	unsigned long gb;
2103

2104 2105 2106 2107 2108 2109
	/*
	 * If we don't have swap space, anonymous page deactivation
	 * is pointless.
	 */
	if (!file && !total_swap_pages)
		return false;
2110

2111 2112
	inactive = lruvec_lru_size(lruvec, inactive_lru, sc->reclaim_idx);
	active = lruvec_lru_size(lruvec, active_lru, sc->reclaim_idx);
2113

2114
	if (memcg)
2115
		refaults = memcg_page_state(memcg, WORKINGSET_ACTIVATE);
2116
	else
2117 2118 2119 2120 2121 2122 2123 2124 2125 2126 2127 2128 2129 2130 2131 2132
		refaults = node_page_state(pgdat, WORKINGSET_ACTIVATE);

	/*
	 * When refaults are being observed, it means a new workingset
	 * is being established. Disable active list protection to get
	 * rid of the stale workingset quickly.
	 */
	if (file && actual_reclaim && lruvec->refaults != refaults) {
		inactive_ratio = 0;
	} else {
		gb = (inactive + active) >> (30 - PAGE_SHIFT);
		if (gb)
			inactive_ratio = int_sqrt(10 * gb);
		else
			inactive_ratio = 1;
	}
2133

2134 2135 2136 2137 2138
	if (actual_reclaim)
		trace_mm_vmscan_inactive_list_is_low(pgdat->node_id, sc->reclaim_idx,
			lruvec_lru_size(lruvec, inactive_lru, MAX_NR_ZONES), inactive,
			lruvec_lru_size(lruvec, active_lru, MAX_NR_ZONES), active,
			inactive_ratio, file);
2139

2140
	return inactive * inactive_ratio < active;
2141 2142
}

2143
static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
2144 2145
				 struct lruvec *lruvec, struct mem_cgroup *memcg,
				 struct scan_control *sc)
2146
{
2147
	if (is_active_lru(lru)) {
2148 2149
		if (inactive_list_is_low(lruvec, is_file_lru(lru),
					 memcg, sc, true))
2150
			shrink_active_list(nr_to_scan, lruvec, sc, lru);
2151 2152 2153
		return 0;
	}

2154
	return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
2155 2156
}

2157 2158 2159 2160 2161 2162 2163
enum scan_balance {
	SCAN_EQUAL,
	SCAN_FRACT,
	SCAN_ANON,
	SCAN_FILE,
};

2164 2165 2166 2167 2168 2169
/*
 * 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.
 *
W
Wanpeng Li 已提交
2170 2171
 * 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
2172
 */
2173
static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
2174 2175
			   struct scan_control *sc, unsigned long *nr,
			   unsigned long *lru_pages)
2176
{
2177
	int swappiness = mem_cgroup_swappiness(memcg);
2178 2179 2180
	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
	u64 fraction[2];
	u64 denominator = 0;	/* gcc */
M
Mel Gorman 已提交
2181
	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
2182
	unsigned long anon_prio, file_prio;
2183
	enum scan_balance scan_balance;
2184
	unsigned long anon, file;
2185
	unsigned long ap, fp;
H
Hugh Dickins 已提交
2186
	enum lru_list lru;
2187 2188

	/* If we have no swap space, do not bother scanning anon pages. */
2189
	if (!sc->may_swap || mem_cgroup_get_nr_swap_pages(memcg) <= 0) {
2190
		scan_balance = SCAN_FILE;
2191 2192
		goto out;
	}
2193

2194 2195 2196 2197 2198 2199 2200
	/*
	 * 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.
	 */
2201
	if (!global_reclaim(sc) && !swappiness) {
2202
		scan_balance = SCAN_FILE;
2203 2204 2205 2206 2207 2208 2209 2210
		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).
	 */
2211
	if (!sc->priority && swappiness) {
2212
		scan_balance = SCAN_EQUAL;
2213 2214 2215
		goto out;
	}

2216 2217 2218 2219 2220 2221 2222 2223 2224 2225
	/*
	 * 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)) {
M
Mel Gorman 已提交
2226 2227 2228 2229
		unsigned long pgdatfile;
		unsigned long pgdatfree;
		int z;
		unsigned long total_high_wmark = 0;
2230

M
Mel Gorman 已提交
2231 2232 2233 2234 2235 2236
		pgdatfree = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES);
		pgdatfile = node_page_state(pgdat, NR_ACTIVE_FILE) +
			   node_page_state(pgdat, NR_INACTIVE_FILE);

		for (z = 0; z < MAX_NR_ZONES; z++) {
			struct zone *zone = &pgdat->node_zones[z];
2237
			if (!managed_zone(zone))
M
Mel Gorman 已提交
2238 2239 2240 2241
				continue;

			total_high_wmark += high_wmark_pages(zone);
		}
2242

M
Mel Gorman 已提交
2243
		if (unlikely(pgdatfile + pgdatfree <= total_high_wmark)) {
2244 2245 2246 2247 2248 2249 2250 2251 2252 2253 2254
			/*
			 * Force SCAN_ANON if there are enough inactive
			 * anonymous pages on the LRU in eligible zones.
			 * Otherwise, the small LRU gets thrashed.
			 */
			if (!inactive_list_is_low(lruvec, false, memcg, sc, false) &&
			    lruvec_lru_size(lruvec, LRU_INACTIVE_ANON, sc->reclaim_idx)
					>> sc->priority) {
				scan_balance = SCAN_ANON;
				goto out;
			}
2255 2256 2257
		}
	}

2258
	/*
2259 2260 2261 2262 2263 2264 2265
	 * If there is enough inactive page cache, i.e. if the size of the
	 * inactive list is greater than that of the active list *and* the
	 * inactive list actually has some pages to scan on this priority, we
	 * do not reclaim anything from the anonymous working set right now.
	 * Without the second condition we could end up never scanning an
	 * lruvec even if it has plenty of old anonymous pages unless the
	 * system is under heavy pressure.
2266
	 */
2267
	if (!inactive_list_is_low(lruvec, true, memcg, sc, false) &&
2268
	    lruvec_lru_size(lruvec, LRU_INACTIVE_FILE, sc->reclaim_idx) >> sc->priority) {
2269
		scan_balance = SCAN_FILE;
2270 2271 2272
		goto out;
	}

2273 2274
	scan_balance = SCAN_FRACT;

2275 2276 2277 2278
	/*
	 * With swappiness at 100, anonymous and file have the same priority.
	 * This scanning priority is essentially the inverse of IO cost.
	 */
2279
	anon_prio = swappiness;
H
Hugh Dickins 已提交
2280
	file_prio = 200 - anon_prio;
2281

2282 2283 2284 2285 2286 2287 2288 2289 2290 2291 2292
	/*
	 * 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]
	 */
2293

2294 2295 2296 2297
	anon  = lruvec_lru_size(lruvec, LRU_ACTIVE_ANON, MAX_NR_ZONES) +
		lruvec_lru_size(lruvec, LRU_INACTIVE_ANON, MAX_NR_ZONES);
	file  = lruvec_lru_size(lruvec, LRU_ACTIVE_FILE, MAX_NR_ZONES) +
		lruvec_lru_size(lruvec, LRU_INACTIVE_FILE, MAX_NR_ZONES);
2298

M
Mel Gorman 已提交
2299
	spin_lock_irq(&pgdat->lru_lock);
2300 2301 2302
	if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
		reclaim_stat->recent_scanned[0] /= 2;
		reclaim_stat->recent_rotated[0] /= 2;
2303 2304
	}

2305 2306 2307
	if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
		reclaim_stat->recent_scanned[1] /= 2;
		reclaim_stat->recent_rotated[1] /= 2;
2308 2309 2310
	}

	/*
2311 2312 2313
	 * 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.
2314
	 */
2315
	ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
2316
	ap /= reclaim_stat->recent_rotated[0] + 1;
2317

2318
	fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
2319
	fp /= reclaim_stat->recent_rotated[1] + 1;
M
Mel Gorman 已提交
2320
	spin_unlock_irq(&pgdat->lru_lock);
2321

2322 2323 2324 2325
	fraction[0] = ap;
	fraction[1] = fp;
	denominator = ap + fp + 1;
out:
2326 2327 2328 2329 2330
	*lru_pages = 0;
	for_each_evictable_lru(lru) {
		int file = is_file_lru(lru);
		unsigned long size;
		unsigned long scan;
2331

2332 2333 2334 2335 2336 2337 2338 2339
		size = lruvec_lru_size(lruvec, lru, sc->reclaim_idx);
		scan = size >> sc->priority;
		/*
		 * If the cgroup's already been deleted, make sure to
		 * scrape out the remaining cache.
		 */
		if (!scan && !mem_cgroup_online(memcg))
			scan = min(size, SWAP_CLUSTER_MAX);
2340

2341 2342 2343 2344 2345
		switch (scan_balance) {
		case SCAN_EQUAL:
			/* Scan lists relative to size */
			break;
		case SCAN_FRACT:
2346
			/*
2347 2348
			 * Scan types proportional to swappiness and
			 * their relative recent reclaim efficiency.
2349
			 */
2350 2351 2352 2353 2354 2355 2356 2357 2358 2359 2360 2361 2362 2363
			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();
2364
		}
2365 2366 2367

		*lru_pages += size;
		nr[lru] = scan;
2368
	}
2369
}
2370

2371
/*
2372
 * This is a basic per-node page freer.  Used by both kswapd and direct reclaim.
2373
 */
2374
static void shrink_node_memcg(struct pglist_data *pgdat, struct mem_cgroup *memcg,
2375
			      struct scan_control *sc, unsigned long *lru_pages)
2376
{
2377
	struct lruvec *lruvec = mem_cgroup_lruvec(pgdat, memcg);
2378
	unsigned long nr[NR_LRU_LISTS];
2379
	unsigned long targets[NR_LRU_LISTS];
2380 2381 2382 2383 2384
	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;
2385
	bool scan_adjusted;
2386

2387
	get_scan_count(lruvec, memcg, sc, nr, lru_pages);
2388

2389 2390 2391
	/* Record the original scan target for proportional adjustments later */
	memcpy(targets, nr, sizeof(nr));

2392 2393 2394 2395 2396 2397 2398 2399 2400 2401 2402 2403 2404 2405
	/*
	 * 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);

2406 2407 2408
	blk_start_plug(&plug);
	while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
					nr[LRU_INACTIVE_FILE]) {
2409 2410 2411
		unsigned long nr_anon, nr_file, percentage;
		unsigned long nr_scanned;

2412 2413 2414 2415 2416 2417
		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,
2418
							    lruvec, memcg, sc);
2419 2420
			}
		}
2421

2422 2423
		cond_resched();

2424 2425 2426 2427 2428
		if (nr_reclaimed < nr_to_reclaim || scan_adjusted)
			continue;

		/*
		 * For kswapd and memcg, reclaim at least the number of pages
2429
		 * requested. Ensure that the anon and file LRUs are scanned
2430 2431 2432 2433 2434 2435 2436
		 * 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];

2437 2438 2439 2440 2441 2442 2443 2444 2445
		/*
		 * 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;

2446 2447 2448 2449 2450 2451 2452 2453 2454 2455 2456 2457 2458 2459 2460 2461 2462 2463 2464 2465 2466 2467 2468 2469 2470 2471 2472 2473 2474 2475 2476
		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;
2477 2478 2479 2480 2481 2482 2483 2484
	}
	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.
	 */
2485
	if (inactive_list_is_low(lruvec, false, memcg, sc, true))
2486 2487 2488 2489
		shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
				   sc, LRU_ACTIVE_ANON);
}

M
Mel Gorman 已提交
2490
/* Use reclaim/compaction for costly allocs or under memory pressure */
2491
static bool in_reclaim_compaction(struct scan_control *sc)
M
Mel Gorman 已提交
2492
{
2493
	if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
M
Mel Gorman 已提交
2494
			(sc->order > PAGE_ALLOC_COSTLY_ORDER ||
2495
			 sc->priority < DEF_PRIORITY - 2))
M
Mel Gorman 已提交
2496 2497 2498 2499 2500
		return true;

	return false;
}

2501
/*
M
Mel Gorman 已提交
2502 2503 2504 2505 2506
 * 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.
2507
 */
2508
static inline bool should_continue_reclaim(struct pglist_data *pgdat,
2509 2510 2511 2512 2513 2514
					unsigned long nr_reclaimed,
					unsigned long nr_scanned,
					struct scan_control *sc)
{
	unsigned long pages_for_compaction;
	unsigned long inactive_lru_pages;
2515
	int z;
2516 2517

	/* If not in reclaim/compaction mode, stop */
2518
	if (!in_reclaim_compaction(sc))
2519 2520
		return false;

2521
	/* Consider stopping depending on scan and reclaim activity */
2522
	if (sc->gfp_mask & __GFP_RETRY_MAYFAIL) {
2523
		/*
2524
		 * For __GFP_RETRY_MAYFAIL allocations, stop reclaiming if the
2525 2526
		 * full LRU list has been scanned and we are still failing
		 * to reclaim pages. This full LRU scan is potentially
2527
		 * expensive but a __GFP_RETRY_MAYFAIL caller really wants to succeed
2528 2529 2530 2531 2532
		 */
		if (!nr_reclaimed && !nr_scanned)
			return false;
	} else {
		/*
2533
		 * For non-__GFP_RETRY_MAYFAIL allocations which can presumably
2534 2535 2536 2537 2538 2539 2540 2541 2542
		 * 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;
	}
2543 2544 2545 2546 2547

	/*
	 * If we have not reclaimed enough pages for compaction and the
	 * inactive lists are large enough, continue reclaiming
	 */
2548
	pages_for_compaction = compact_gap(sc->order);
2549
	inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE);
2550
	if (get_nr_swap_pages() > 0)
2551
		inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);
2552 2553 2554 2555 2556
	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 */
2557 2558
	for (z = 0; z <= sc->reclaim_idx; z++) {
		struct zone *zone = &pgdat->node_zones[z];
2559
		if (!managed_zone(zone))
2560 2561 2562
			continue;

		switch (compaction_suitable(zone, sc->order, 0, sc->reclaim_idx)) {
2563
		case COMPACT_SUCCESS:
2564 2565 2566 2567 2568 2569
		case COMPACT_CONTINUE:
			return false;
		default:
			/* check next zone */
			;
		}
2570
	}
2571
	return true;
2572 2573
}

2574
static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
L
Linus Torvalds 已提交
2575
{
2576
	struct reclaim_state *reclaim_state = current->reclaim_state;
2577
	unsigned long nr_reclaimed, nr_scanned;
2578
	bool reclaimable = false;
L
Linus Torvalds 已提交
2579

2580 2581 2582
	do {
		struct mem_cgroup *root = sc->target_mem_cgroup;
		struct mem_cgroup_reclaim_cookie reclaim = {
2583
			.pgdat = pgdat,
2584 2585
			.priority = sc->priority,
		};
2586
		unsigned long node_lru_pages = 0;
2587
		struct mem_cgroup *memcg;
2588

2589 2590
		nr_reclaimed = sc->nr_reclaimed;
		nr_scanned = sc->nr_scanned;
L
Linus Torvalds 已提交
2591

2592 2593
		memcg = mem_cgroup_iter(root, NULL, &reclaim);
		do {
2594
			unsigned long lru_pages;
2595
			unsigned long reclaimed;
2596
			unsigned long scanned;
2597

2598
			if (mem_cgroup_low(root, memcg)) {
2599 2600
				if (!sc->memcg_low_reclaim) {
					sc->memcg_low_skipped = 1;
2601
					continue;
2602
				}
2603
				mem_cgroup_event(memcg, MEMCG_LOW);
2604 2605
			}

2606
			reclaimed = sc->nr_reclaimed;
2607
			scanned = sc->nr_scanned;
2608 2609
			shrink_node_memcg(pgdat, memcg, sc, &lru_pages);
			node_lru_pages += lru_pages;
2610

2611
			if (memcg)
2612
				shrink_slab(sc->gfp_mask, pgdat->node_id,
2613
					    memcg, sc->priority);
2614

2615 2616 2617 2618 2619
			/* Record the group's reclaim efficiency */
			vmpressure(sc->gfp_mask, memcg, false,
				   sc->nr_scanned - scanned,
				   sc->nr_reclaimed - reclaimed);

2620
			/*
2621 2622
			 * Direct reclaim and kswapd have to scan all memory
			 * cgroups to fulfill the overall scan target for the
2623
			 * node.
2624 2625 2626 2627 2628
			 *
			 * 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.
2629
			 */
2630 2631
			if (!global_reclaim(sc) &&
					sc->nr_reclaimed >= sc->nr_to_reclaim) {
2632 2633 2634
				mem_cgroup_iter_break(root, memcg);
				break;
			}
2635
		} while ((memcg = mem_cgroup_iter(root, memcg, &reclaim)));
2636

2637
		if (global_reclaim(sc))
2638
			shrink_slab(sc->gfp_mask, pgdat->node_id, NULL,
2639
				    sc->priority);
2640 2641 2642 2643

		if (reclaim_state) {
			sc->nr_reclaimed += reclaim_state->reclaimed_slab;
			reclaim_state->reclaimed_slab = 0;
2644 2645
		}

2646 2647
		/* Record the subtree's reclaim efficiency */
		vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true,
2648 2649 2650
			   sc->nr_scanned - nr_scanned,
			   sc->nr_reclaimed - nr_reclaimed);

2651 2652 2653
		if (sc->nr_reclaimed - nr_reclaimed)
			reclaimable = true;

2654
	} while (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed,
2655
					 sc->nr_scanned - nr_scanned, sc));
2656

2657 2658 2659 2660 2661 2662 2663 2664 2665
	/*
	 * Kswapd gives up on balancing particular nodes after too
	 * many failures to reclaim anything from them and goes to
	 * sleep. On reclaim progress, reset the failure counter. A
	 * successful direct reclaim run will revive a dormant kswapd.
	 */
	if (reclaimable)
		pgdat->kswapd_failures = 0;

2666
	return reclaimable;
2667 2668
}

2669
/*
2670 2671 2672
 * Returns true if compaction should go ahead for a costly-order request, or
 * the allocation would already succeed without compaction. Return false if we
 * should reclaim first.
2673
 */
2674
static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
2675
{
M
Mel Gorman 已提交
2676
	unsigned long watermark;
2677
	enum compact_result suitable;
2678

2679 2680 2681 2682 2683 2684 2685
	suitable = compaction_suitable(zone, sc->order, 0, sc->reclaim_idx);
	if (suitable == COMPACT_SUCCESS)
		/* Allocation should succeed already. Don't reclaim. */
		return true;
	if (suitable == COMPACT_SKIPPED)
		/* Compaction cannot yet proceed. Do reclaim. */
		return false;
2686

2687
	/*
2688 2689 2690 2691 2692 2693 2694
	 * Compaction is already possible, but it takes time to run and there
	 * are potentially other callers using the pages just freed. So proceed
	 * with reclaim to make a buffer of free pages available to give
	 * compaction a reasonable chance of completing and allocating the page.
	 * Note that we won't actually reclaim the whole buffer in one attempt
	 * as the target watermark in should_continue_reclaim() is lower. But if
	 * we are already above the high+gap watermark, don't reclaim at all.
2695
	 */
2696
	watermark = high_wmark_pages(zone) + compact_gap(sc->order);
2697

2698
	return zone_watermark_ok_safe(zone, 0, watermark, sc->reclaim_idx);
2699 2700
}

L
Linus Torvalds 已提交
2701 2702 2703 2704 2705 2706 2707 2708
/*
 * 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.
 *
 * If a zone is deemed to be full of pinned pages then just give it a light
 * scan then give up on it.
 */
M
Michal Hocko 已提交
2709
static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
L
Linus Torvalds 已提交
2710
{
2711
	struct zoneref *z;
2712
	struct zone *zone;
2713 2714
	unsigned long nr_soft_reclaimed;
	unsigned long nr_soft_scanned;
2715
	gfp_t orig_mask;
2716
	pg_data_t *last_pgdat = NULL;
2717

2718 2719 2720 2721 2722
	/*
	 * 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
	 */
2723
	orig_mask = sc->gfp_mask;
2724
	if (buffer_heads_over_limit) {
2725
		sc->gfp_mask |= __GFP_HIGHMEM;
2726
		sc->reclaim_idx = gfp_zone(sc->gfp_mask);
2727
	}
2728

2729
	for_each_zone_zonelist_nodemask(zone, z, zonelist,
2730
					sc->reclaim_idx, sc->nodemask) {
2731 2732 2733 2734
		/*
		 * Take care memory controller reclaiming has small influence
		 * to global LRU.
		 */
2735
		if (global_reclaim(sc)) {
2736 2737
			if (!cpuset_zone_allowed(zone,
						 GFP_KERNEL | __GFP_HARDWALL))
2738
				continue;
2739

2740 2741 2742 2743 2744 2745 2746 2747 2748 2749 2750
			/*
			 * 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 &&
2751
			    compaction_ready(zone, sc)) {
2752 2753
				sc->compaction_ready = true;
				continue;
2754
			}
2755

2756 2757 2758 2759 2760 2761 2762 2763 2764
			/*
			 * Shrink each node in the zonelist once. If the
			 * zonelist is ordered by zone (not the default) then a
			 * node may be shrunk multiple times but in that case
			 * the user prefers lower zones being preserved.
			 */
			if (zone->zone_pgdat == last_pgdat)
				continue;

2765 2766 2767 2768 2769 2770 2771
			/*
			 * 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;
2772
			nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone->zone_pgdat,
2773 2774 2775 2776
						sc->order, sc->gfp_mask,
						&nr_soft_scanned);
			sc->nr_reclaimed += nr_soft_reclaimed;
			sc->nr_scanned += nr_soft_scanned;
2777
			/* need some check for avoid more shrink_zone() */
2778
		}
2779

2780 2781 2782 2783
		/* See comment about same check for global reclaim above */
		if (zone->zone_pgdat == last_pgdat)
			continue;
		last_pgdat = zone->zone_pgdat;
2784
		shrink_node(zone->zone_pgdat, sc);
L
Linus Torvalds 已提交
2785
	}
2786

2787 2788 2789 2790 2791
	/*
	 * Restore to original mask to avoid the impact on the caller if we
	 * promoted it to __GFP_HIGHMEM.
	 */
	sc->gfp_mask = orig_mask;
L
Linus Torvalds 已提交
2792
}
2793

2794 2795 2796 2797 2798 2799 2800 2801 2802 2803
static void snapshot_refaults(struct mem_cgroup *root_memcg, pg_data_t *pgdat)
{
	struct mem_cgroup *memcg;

	memcg = mem_cgroup_iter(root_memcg, NULL, NULL);
	do {
		unsigned long refaults;
		struct lruvec *lruvec;

		if (memcg)
2804
			refaults = memcg_page_state(memcg, WORKINGSET_ACTIVATE);
2805 2806 2807 2808 2809 2810 2811 2812
		else
			refaults = node_page_state(pgdat, WORKINGSET_ACTIVATE);

		lruvec = mem_cgroup_lruvec(pgdat, memcg);
		lruvec->refaults = refaults;
	} while ((memcg = mem_cgroup_iter(root_memcg, memcg, NULL)));
}

L
Linus Torvalds 已提交
2813 2814 2815 2816 2817 2818 2819 2820
/*
 * 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
2821 2822 2823 2824
 * 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.
2825 2826 2827
 *
 * returns:	0, if no pages reclaimed
 * 		else, the number of pages reclaimed
L
Linus Torvalds 已提交
2828
 */
2829
static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2830
					  struct scan_control *sc)
L
Linus Torvalds 已提交
2831
{
2832
	int initial_priority = sc->priority;
2833 2834 2835
	pg_data_t *last_pgdat;
	struct zoneref *z;
	struct zone *zone;
2836
retry:
2837 2838
	delayacct_freepages_start();

2839
	if (global_reclaim(sc))
2840
		__count_zid_vm_events(ALLOCSTALL, sc->reclaim_idx, 1);
L
Linus Torvalds 已提交
2841

2842
	do {
2843 2844
		vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
				sc->priority);
2845
		sc->nr_scanned = 0;
M
Michal Hocko 已提交
2846
		shrink_zones(zonelist, sc);
2847

2848
		if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2849 2850 2851 2852
			break;

		if (sc->compaction_ready)
			break;
L
Linus Torvalds 已提交
2853

2854 2855 2856 2857 2858 2859
		/*
		 * If we're getting trouble reclaiming, start doing
		 * writepage even in laptop mode.
		 */
		if (sc->priority < DEF_PRIORITY - 2)
			sc->may_writepage = 1;
2860
	} while (--sc->priority >= 0);
2861

2862 2863 2864 2865 2866 2867 2868 2869 2870
	last_pgdat = NULL;
	for_each_zone_zonelist_nodemask(zone, z, zonelist, sc->reclaim_idx,
					sc->nodemask) {
		if (zone->zone_pgdat == last_pgdat)
			continue;
		last_pgdat = zone->zone_pgdat;
		snapshot_refaults(sc->target_mem_cgroup, zone->zone_pgdat);
	}

2871 2872
	delayacct_freepages_end();

2873 2874 2875
	if (sc->nr_reclaimed)
		return sc->nr_reclaimed;

2876
	/* Aborted reclaim to try compaction? don't OOM, then */
2877
	if (sc->compaction_ready)
2878 2879
		return 1;

2880
	/* Untapped cgroup reserves?  Don't OOM, retry. */
2881
	if (sc->memcg_low_skipped) {
2882
		sc->priority = initial_priority;
2883 2884
		sc->memcg_low_reclaim = 1;
		sc->memcg_low_skipped = 0;
2885 2886 2887
		goto retry;
	}

2888
	return 0;
L
Linus Torvalds 已提交
2889 2890
}

2891
static bool allow_direct_reclaim(pg_data_t *pgdat)
2892 2893 2894 2895 2896 2897 2898
{
	struct zone *zone;
	unsigned long pfmemalloc_reserve = 0;
	unsigned long free_pages = 0;
	int i;
	bool wmark_ok;

2899 2900 2901
	if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
		return true;

2902 2903
	for (i = 0; i <= ZONE_NORMAL; i++) {
		zone = &pgdat->node_zones[i];
2904 2905 2906 2907
		if (!managed_zone(zone))
			continue;

		if (!zone_reclaimable_pages(zone))
2908 2909
			continue;

2910 2911 2912 2913
		pfmemalloc_reserve += min_wmark_pages(zone);
		free_pages += zone_page_state(zone, NR_FREE_PAGES);
	}

2914 2915 2916 2917
	/* If there are no reserves (unexpected config) then do not throttle */
	if (!pfmemalloc_reserve)
		return true;

2918 2919 2920 2921
	wmark_ok = free_pages > pfmemalloc_reserve / 2;

	/* kswapd must be awake if processes are being throttled */
	if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
2922
		pgdat->kswapd_classzone_idx = min(pgdat->kswapd_classzone_idx,
2923 2924 2925 2926 2927 2928 2929 2930 2931 2932 2933
						(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
2934 2935 2936 2937
 * 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.
2938
 */
2939
static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
2940 2941
					nodemask_t *nodemask)
{
2942
	struct zoneref *z;
2943
	struct zone *zone;
2944
	pg_data_t *pgdat = NULL;
2945 2946 2947 2948 2949 2950 2951 2952 2953

	/*
	 * 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)
2954 2955 2956 2957 2958 2959 2960 2961
		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;
2962

2963 2964 2965 2966 2967 2968 2969 2970 2971 2972 2973 2974 2975 2976 2977
	/*
	 * 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,
2978
					gfp_zone(gfp_mask), nodemask) {
2979 2980 2981 2982 2983
		if (zone_idx(zone) > ZONE_NORMAL)
			continue;

		/* Throttle based on the first usable node */
		pgdat = zone->zone_pgdat;
2984
		if (allow_direct_reclaim(pgdat))
2985 2986 2987 2988 2989 2990
			goto out;
		break;
	}

	/* If no zone was usable by the allocation flags then do not throttle */
	if (!pgdat)
2991
		goto out;
2992

2993 2994 2995
	/* Account for the throttling */
	count_vm_event(PGSCAN_DIRECT_THROTTLE);

2996 2997 2998 2999 3000 3001 3002 3003 3004 3005
	/*
	 * 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,
3006
			allow_direct_reclaim(pgdat), HZ);
3007 3008

		goto check_pending;
3009 3010 3011 3012
	}

	/* Throttle until kswapd wakes the process */
	wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
3013
		allow_direct_reclaim(pgdat));
3014 3015 3016 3017 3018 3019 3020

check_pending:
	if (fatal_signal_pending(current))
		return true;

out:
	return false;
3021 3022
}

3023
unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
3024
				gfp_t gfp_mask, nodemask_t *nodemask)
3025
{
3026
	unsigned long nr_reclaimed;
3027
	struct scan_control sc = {
3028
		.nr_to_reclaim = SWAP_CLUSTER_MAX,
3029
		.gfp_mask = current_gfp_context(gfp_mask),
3030
		.reclaim_idx = gfp_zone(gfp_mask),
3031 3032 3033
		.order = order,
		.nodemask = nodemask,
		.priority = DEF_PRIORITY,
3034
		.may_writepage = !laptop_mode,
3035
		.may_unmap = 1,
3036
		.may_swap = 1,
3037 3038
	};

3039
	/*
3040 3041 3042
	 * 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.
3043
	 */
3044
	if (throttle_direct_reclaim(sc.gfp_mask, zonelist, nodemask))
3045 3046
		return 1;

3047 3048
	trace_mm_vmscan_direct_reclaim_begin(order,
				sc.may_writepage,
3049
				sc.gfp_mask,
3050
				sc.reclaim_idx);
3051

3052
	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3053 3054 3055 3056

	trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);

	return nr_reclaimed;
3057 3058
}

A
Andrew Morton 已提交
3059
#ifdef CONFIG_MEMCG
3060

3061
unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg,
3062
						gfp_t gfp_mask, bool noswap,
3063
						pg_data_t *pgdat,
3064
						unsigned long *nr_scanned)
3065 3066
{
	struct scan_control sc = {
3067
		.nr_to_reclaim = SWAP_CLUSTER_MAX,
3068
		.target_mem_cgroup = memcg,
3069 3070
		.may_writepage = !laptop_mode,
		.may_unmap = 1,
3071
		.reclaim_idx = MAX_NR_ZONES - 1,
3072 3073
		.may_swap = !noswap,
	};
3074
	unsigned long lru_pages;
3075

3076 3077
	sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
			(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
3078

3079
	trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
3080
						      sc.may_writepage,
3081 3082
						      sc.gfp_mask,
						      sc.reclaim_idx);
3083

3084 3085 3086
	/*
	 * NOTE: Although we can get the priority field, using it
	 * here is not a good idea, since it limits the pages we can scan.
3087
	 * if we don't reclaim here, the shrink_node from balance_pgdat
3088 3089 3090
	 * will pick up pages from other mem cgroup's as well. We hack
	 * the priority and make it zero.
	 */
3091
	shrink_node_memcg(pgdat, memcg, &sc, &lru_pages);
3092 3093 3094

	trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);

3095
	*nr_scanned = sc.nr_scanned;
3096 3097 3098
	return sc.nr_reclaimed;
}

3099
unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
3100
					   unsigned long nr_pages,
K
KOSAKI Motohiro 已提交
3101
					   gfp_t gfp_mask,
3102
					   bool may_swap)
3103
{
3104
	struct zonelist *zonelist;
3105
	unsigned long nr_reclaimed;
3106
	int nid;
3107
	unsigned int noreclaim_flag;
3108
	struct scan_control sc = {
3109
		.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3110
		.gfp_mask = (current_gfp_context(gfp_mask) & GFP_RECLAIM_MASK) |
3111
				(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
3112
		.reclaim_idx = MAX_NR_ZONES - 1,
3113 3114 3115 3116
		.target_mem_cgroup = memcg,
		.priority = DEF_PRIORITY,
		.may_writepage = !laptop_mode,
		.may_unmap = 1,
3117
		.may_swap = may_swap,
3118
	};
3119

3120 3121 3122 3123 3124
	/*
	 * 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.
	 */
3125
	nid = mem_cgroup_select_victim_node(memcg);
3126

3127
	zonelist = &NODE_DATA(nid)->node_zonelists[ZONELIST_FALLBACK];
3128 3129 3130

	trace_mm_vmscan_memcg_reclaim_begin(0,
					    sc.may_writepage,
3131 3132
					    sc.gfp_mask,
					    sc.reclaim_idx);
3133

3134
	noreclaim_flag = memalloc_noreclaim_save();
3135
	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3136
	memalloc_noreclaim_restore(noreclaim_flag);
3137 3138 3139 3140

	trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);

	return nr_reclaimed;
3141 3142 3143
}
#endif

3144
static void age_active_anon(struct pglist_data *pgdat,
3145
				struct scan_control *sc)
3146
{
3147
	struct mem_cgroup *memcg;
3148

3149 3150 3151 3152 3153
	if (!total_swap_pages)
		return;

	memcg = mem_cgroup_iter(NULL, NULL, NULL);
	do {
3154
		struct lruvec *lruvec = mem_cgroup_lruvec(pgdat, memcg);
3155

3156
		if (inactive_list_is_low(lruvec, false, memcg, sc, true))
3157
			shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
3158
					   sc, LRU_ACTIVE_ANON);
3159 3160 3161

		memcg = mem_cgroup_iter(NULL, memcg, NULL);
	} while (memcg);
3162 3163
}

3164 3165 3166 3167 3168
/*
 * Returns true if there is an eligible zone balanced for the request order
 * and classzone_idx
 */
static bool pgdat_balanced(pg_data_t *pgdat, int order, int classzone_idx)
3169
{
3170 3171 3172
	int i;
	unsigned long mark = -1;
	struct zone *zone;
3173

3174 3175
	for (i = 0; i <= classzone_idx; i++) {
		zone = pgdat->node_zones + i;
3176

3177 3178 3179 3180 3181 3182 3183 3184 3185 3186 3187 3188 3189 3190 3191 3192 3193
		if (!managed_zone(zone))
			continue;

		mark = high_wmark_pages(zone);
		if (zone_watermark_ok_safe(zone, order, mark, classzone_idx))
			return true;
	}

	/*
	 * If a node has no populated zone within classzone_idx, it does not
	 * need balancing by definition. This can happen if a zone-restricted
	 * allocation tries to wake a remote kswapd.
	 */
	if (mark == -1)
		return true;

	return false;
3194 3195
}

3196 3197 3198 3199 3200 3201 3202 3203
/* Clear pgdat state for congested, dirty or under writeback. */
static void clear_pgdat_congested(pg_data_t *pgdat)
{
	clear_bit(PGDAT_CONGESTED, &pgdat->flags);
	clear_bit(PGDAT_DIRTY, &pgdat->flags);
	clear_bit(PGDAT_WRITEBACK, &pgdat->flags);
}

3204 3205 3206 3207 3208 3209
/*
 * 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
 */
3210
static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, int classzone_idx)
3211
{
3212
	/*
3213
	 * The throttled processes are normally woken up in balance_pgdat() as
3214
	 * soon as allow_direct_reclaim() is true. But there is a potential
3215 3216 3217 3218 3219 3220 3221 3222 3223
	 * 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().
3224
	 */
3225 3226
	if (waitqueue_active(&pgdat->pfmemalloc_wait))
		wake_up_all(&pgdat->pfmemalloc_wait);
3227

3228 3229 3230 3231
	/* Hopeless node, leave it to direct reclaim */
	if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
		return true;

3232 3233 3234
	if (pgdat_balanced(pgdat, order, classzone_idx)) {
		clear_pgdat_congested(pgdat);
		return true;
3235 3236
	}

3237
	return false;
3238 3239
}

3240
/*
3241 3242
 * kswapd shrinks a node of pages that are at or below the highest usable
 * zone that is currently unbalanced.
3243 3244
 *
 * Returns true if kswapd scanned at least the requested number of pages to
3245 3246
 * 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.
3247
 */
3248
static bool kswapd_shrink_node(pg_data_t *pgdat,
3249
			       struct scan_control *sc)
3250
{
3251 3252
	struct zone *zone;
	int z;
3253

3254 3255
	/* Reclaim a number of pages proportional to the number of zones */
	sc->nr_to_reclaim = 0;
3256
	for (z = 0; z <= sc->reclaim_idx; z++) {
3257
		zone = pgdat->node_zones + z;
3258
		if (!managed_zone(zone))
3259
			continue;
3260

3261 3262
		sc->nr_to_reclaim += max(high_wmark_pages(zone), SWAP_CLUSTER_MAX);
	}
3263 3264

	/*
3265 3266
	 * Historically care was taken to put equal pressure on all zones but
	 * now pressure is applied based on node LRU order.
3267
	 */
3268
	shrink_node(pgdat, sc);
3269

3270
	/*
3271 3272 3273 3274 3275
	 * Fragmentation may mean that the system cannot be rebalanced for
	 * high-order allocations. If twice the allocation size has been
	 * reclaimed then recheck watermarks only at order-0 to prevent
	 * excessive reclaim. Assume that a process requested a high-order
	 * can direct reclaim/compact.
3276
	 */
3277
	if (sc->order && sc->nr_reclaimed >= compact_gap(sc->order))
3278
		sc->order = 0;
3279

3280
	return sc->nr_scanned >= sc->nr_to_reclaim;
3281 3282
}

L
Linus Torvalds 已提交
3283
/*
3284 3285 3286
 * For kswapd, balance_pgdat() will reclaim pages across a node from zones
 * that are eligible for use by the caller until at least one zone is
 * balanced.
L
Linus Torvalds 已提交
3287
 *
3288
 * Returns the order kswapd finished reclaiming at.
L
Linus Torvalds 已提交
3289 3290
 *
 * kswapd scans the zones in the highmem->normal->dma direction.  It skips
3291
 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
3292 3293 3294
 * found to have free_pages <= high_wmark_pages(zone), any page is that zone
 * or lower is eligible for reclaim until at least one usable zone is
 * balanced.
L
Linus Torvalds 已提交
3295
 */
3296
static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
L
Linus Torvalds 已提交
3297 3298
{
	int i;
3299 3300
	unsigned long nr_soft_reclaimed;
	unsigned long nr_soft_scanned;
3301
	struct zone *zone;
3302 3303
	struct scan_control sc = {
		.gfp_mask = GFP_KERNEL,
3304
		.order = order,
3305
		.priority = DEF_PRIORITY,
3306
		.may_writepage = !laptop_mode,
3307
		.may_unmap = 1,
3308
		.may_swap = 1,
3309
	};
3310
	count_vm_event(PAGEOUTRUN);
L
Linus Torvalds 已提交
3311

3312
	do {
3313
		unsigned long nr_reclaimed = sc.nr_reclaimed;
3314 3315
		bool raise_priority = true;

3316
		sc.reclaim_idx = classzone_idx;
L
Linus Torvalds 已提交
3317

3318
		/*
3319 3320 3321 3322 3323 3324 3325 3326
		 * If the number of buffer_heads exceeds the maximum allowed
		 * then consider reclaiming from all zones. This has a dual
		 * purpose -- on 64-bit systems it is expected that
		 * buffer_heads are stripped during active rotation. On 32-bit
		 * systems, highmem pages can pin lowmem memory and shrinking
		 * buffers can relieve lowmem pressure. Reclaim may still not
		 * go ahead if all eligible zones for the original allocation
		 * request are balanced to avoid excessive reclaim from kswapd.
3327 3328 3329 3330
		 */
		if (buffer_heads_over_limit) {
			for (i = MAX_NR_ZONES - 1; i >= 0; i--) {
				zone = pgdat->node_zones + i;
3331
				if (!managed_zone(zone))
3332
					continue;
3333

3334
				sc.reclaim_idx = i;
A
Andrew Morton 已提交
3335
				break;
L
Linus Torvalds 已提交
3336 3337
			}
		}
3338

3339
		/*
3340 3341 3342
		 * Only reclaim if there are no eligible zones. Note that
		 * sc.reclaim_idx is not used as buffer_heads_over_limit may
		 * have adjusted it.
3343
		 */
3344 3345
		if (pgdat_balanced(pgdat, sc.order, classzone_idx))
			goto out;
A
Andrew Morton 已提交
3346

3347 3348 3349 3350 3351 3352
		/*
		 * Do some background aging of the anon list, to give
		 * pages a chance to be referenced before reclaiming. All
		 * pages are rotated regardless of classzone as this is
		 * about consistent aging.
		 */
3353
		age_active_anon(pgdat, &sc);
3354

3355 3356 3357 3358
		/*
		 * If we're getting trouble reclaiming, start doing writepage
		 * even in laptop mode.
		 */
3359
		if (sc.priority < DEF_PRIORITY - 2)
3360 3361
			sc.may_writepage = 1;

3362 3363 3364
		/* Call soft limit reclaim before calling shrink_node. */
		sc.nr_scanned = 0;
		nr_soft_scanned = 0;
3365
		nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(pgdat, sc.order,
3366 3367 3368
						sc.gfp_mask, &nr_soft_scanned);
		sc.nr_reclaimed += nr_soft_reclaimed;

L
Linus Torvalds 已提交
3369
		/*
3370 3371 3372
		 * 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.
L
Linus Torvalds 已提交
3373
		 */
3374
		if (kswapd_shrink_node(pgdat, &sc))
3375
			raise_priority = false;
3376 3377 3378 3379 3380 3381 3382

		/*
		 * 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) &&
3383
				allow_direct_reclaim(pgdat))
3384
			wake_up_all(&pgdat->pfmemalloc_wait);
3385

3386 3387 3388
		/* Check if kswapd should be suspending */
		if (try_to_freeze() || kthread_should_stop())
			break;
3389

3390
		/*
3391 3392
		 * Raise priority if scanning rate is too low or there was no
		 * progress in reclaiming pages
3393
		 */
3394 3395
		nr_reclaimed = sc.nr_reclaimed - nr_reclaimed;
		if (raise_priority || !nr_reclaimed)
3396
			sc.priority--;
3397
	} while (sc.priority >= 1);
L
Linus Torvalds 已提交
3398

3399 3400 3401
	if (!sc.nr_reclaimed)
		pgdat->kswapd_failures++;

3402
out:
3403
	snapshot_refaults(NULL, pgdat);
3404
	/*
3405 3406 3407 3408
	 * Return the order kswapd stopped reclaiming at as
	 * prepare_kswapd_sleep() takes it into account. If another caller
	 * entered the allocator slow path while kswapd was awake, order will
	 * remain at the higher level.
3409
	 */
3410
	return sc.order;
L
Linus Torvalds 已提交
3411 3412
}

3413 3414 3415 3416 3417 3418 3419 3420 3421 3422 3423 3424 3425 3426 3427 3428
/*
 * pgdat->kswapd_classzone_idx is the highest zone index that a recent
 * allocation request woke kswapd for. When kswapd has not woken recently,
 * the value is MAX_NR_ZONES which is not a valid index. This compares a
 * given classzone and returns it or the highest classzone index kswapd
 * was recently woke for.
 */
static enum zone_type kswapd_classzone_idx(pg_data_t *pgdat,
					   enum zone_type classzone_idx)
{
	if (pgdat->kswapd_classzone_idx == MAX_NR_ZONES)
		return classzone_idx;

	return max(pgdat->kswapd_classzone_idx, classzone_idx);
}

3429 3430
static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_order,
				unsigned int classzone_idx)
3431 3432 3433 3434 3435 3436 3437 3438 3439
{
	long remaining = 0;
	DEFINE_WAIT(wait);

	if (freezing(current) || kthread_should_stop())
		return;

	prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);

3440 3441 3442 3443 3444 3445 3446
	/*
	 * Try to sleep for a short interval. Note that kcompactd will only be
	 * woken if it is possible to sleep for a short interval. This is
	 * deliberate on the assumption that if reclaim cannot keep an
	 * eligible zone balanced that it's also unlikely that compaction will
	 * succeed.
	 */
3447
	if (prepare_kswapd_sleep(pgdat, reclaim_order, classzone_idx)) {
3448 3449 3450 3451 3452 3453 3454 3455 3456 3457 3458 3459
		/*
		 * Compaction records what page blocks it recently failed to
		 * isolate pages from and skips them in the future scanning.
		 * When kswapd is going to sleep, it is reasonable to assume
		 * that pages and compaction may succeed so reset the cache.
		 */
		reset_isolation_suitable(pgdat);

		/*
		 * We have freed the memory, now we should compact it to make
		 * allocation of the requested order possible.
		 */
3460
		wakeup_kcompactd(pgdat, alloc_order, classzone_idx);
3461

3462
		remaining = schedule_timeout(HZ/10);
3463 3464 3465 3466 3467 3468 3469

		/*
		 * If woken prematurely then reset kswapd_classzone_idx and
		 * order. The values will either be from a wakeup request or
		 * the previous request that slept prematurely.
		 */
		if (remaining) {
3470
			pgdat->kswapd_classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx);
3471 3472 3473
			pgdat->kswapd_order = max(pgdat->kswapd_order, reclaim_order);
		}

3474 3475 3476 3477 3478 3479 3480 3481
		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.
	 */
3482 3483
	if (!remaining &&
	    prepare_kswapd_sleep(pgdat, reclaim_order, classzone_idx)) {
3484 3485 3486 3487 3488 3489 3490 3491 3492 3493 3494
		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);
3495 3496 3497 3498

		if (!kthread_should_stop())
			schedule();

3499 3500 3501 3502 3503 3504 3505 3506 3507 3508
		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);
}

L
Linus Torvalds 已提交
3509 3510
/*
 * The background pageout daemon, started as a kernel thread
3511
 * from the init process.
L
Linus Torvalds 已提交
3512 3513 3514 3515 3516 3517 3518 3519 3520 3521 3522 3523
 *
 * 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)
{
3524 3525
	unsigned int alloc_order, reclaim_order;
	unsigned int classzone_idx = MAX_NR_ZONES - 1;
L
Linus Torvalds 已提交
3526 3527
	pg_data_t *pgdat = (pg_data_t*)p;
	struct task_struct *tsk = current;
3528

L
Linus Torvalds 已提交
3529 3530 3531
	struct reclaim_state reclaim_state = {
		.reclaimed_slab = 0,
	};
3532
	const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
L
Linus Torvalds 已提交
3533

R
Rusty Russell 已提交
3534
	if (!cpumask_empty(cpumask))
3535
		set_cpus_allowed_ptr(tsk, cpumask);
L
Linus Torvalds 已提交
3536 3537 3538 3539 3540 3541 3542 3543 3544 3545 3546 3547 3548 3549
	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).
	 */
3550
	tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
3551
	set_freezable();
L
Linus Torvalds 已提交
3552

3553 3554
	pgdat->kswapd_order = 0;
	pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
L
Linus Torvalds 已提交
3555
	for ( ; ; ) {
3556
		bool ret;
3557

3558 3559 3560
		alloc_order = reclaim_order = pgdat->kswapd_order;
		classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx);

3561 3562 3563
kswapd_try_sleep:
		kswapd_try_to_sleep(pgdat, alloc_order, reclaim_order,
					classzone_idx);
3564

3565 3566
		/* Read the new order and classzone_idx */
		alloc_order = reclaim_order = pgdat->kswapd_order;
3567
		classzone_idx = kswapd_classzone_idx(pgdat, 0);
3568
		pgdat->kswapd_order = 0;
3569
		pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
L
Linus Torvalds 已提交
3570

3571 3572 3573 3574 3575 3576 3577 3578
		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
		 */
3579 3580 3581 3582 3583 3584 3585 3586 3587 3588 3589
		if (ret)
			continue;

		/*
		 * Reclaim begins at the requested order but if a high-order
		 * reclaim fails then kswapd falls back to reclaiming for
		 * order-0. If that happens, kswapd will consider sleeping
		 * for the order it finished reclaiming at (reclaim_order)
		 * but kcompactd is woken to compact for the original
		 * request (alloc_order).
		 */
3590 3591
		trace_mm_vmscan_kswapd_wake(pgdat->node_id, classzone_idx,
						alloc_order);
3592
		fs_reclaim_acquire(GFP_KERNEL);
3593
		reclaim_order = balance_pgdat(pgdat, alloc_order, classzone_idx);
3594
		fs_reclaim_release(GFP_KERNEL);
3595 3596
		if (reclaim_order < alloc_order)
			goto kswapd_try_sleep;
L
Linus Torvalds 已提交
3597
	}
3598

3599
	tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD);
3600
	current->reclaim_state = NULL;
3601

L
Linus Torvalds 已提交
3602 3603 3604 3605 3606 3607
	return 0;
}

/*
 * A zone is low on free memory, so wake its kswapd task to service it.
 */
3608
void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
L
Linus Torvalds 已提交
3609 3610 3611
{
	pg_data_t *pgdat;

3612
	if (!managed_zone(zone))
L
Linus Torvalds 已提交
3613 3614
		return;

3615
	if (!cpuset_zone_allowed(zone, GFP_KERNEL | __GFP_HARDWALL))
L
Linus Torvalds 已提交
3616
		return;
3617
	pgdat = zone->zone_pgdat;
3618 3619
	pgdat->kswapd_classzone_idx = kswapd_classzone_idx(pgdat,
							   classzone_idx);
3620
	pgdat->kswapd_order = max(pgdat->kswapd_order, order);
3621
	if (!waitqueue_active(&pgdat->kswapd_wait))
L
Linus Torvalds 已提交
3622
		return;
3623

3624 3625 3626 3627
	/* Hopeless node, leave it to direct reclaim */
	if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
		return;

3628 3629
	if (pgdat_balanced(pgdat, order, classzone_idx))
		return;
3630

3631
	trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, classzone_idx, order);
3632
	wake_up_interruptible(&pgdat->kswapd_wait);
L
Linus Torvalds 已提交
3633 3634
}

3635
#ifdef CONFIG_HIBERNATION
L
Linus Torvalds 已提交
3636
/*
3637
 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
3638 3639 3640 3641 3642
 * 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
L
Linus Torvalds 已提交
3643
 */
3644
unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
L
Linus Torvalds 已提交
3645
{
3646 3647
	struct reclaim_state reclaim_state;
	struct scan_control sc = {
3648
		.nr_to_reclaim = nr_to_reclaim,
3649
		.gfp_mask = GFP_HIGHUSER_MOVABLE,
3650
		.reclaim_idx = MAX_NR_ZONES - 1,
3651
		.priority = DEF_PRIORITY,
3652
		.may_writepage = 1,
3653 3654
		.may_unmap = 1,
		.may_swap = 1,
3655
		.hibernation_mode = 1,
L
Linus Torvalds 已提交
3656
	};
3657
	struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3658 3659
	struct task_struct *p = current;
	unsigned long nr_reclaimed;
3660
	unsigned int noreclaim_flag;
L
Linus Torvalds 已提交
3661

3662
	noreclaim_flag = memalloc_noreclaim_save();
3663
	fs_reclaim_acquire(sc.gfp_mask);
3664 3665
	reclaim_state.reclaimed_slab = 0;
	p->reclaim_state = &reclaim_state;
3666

3667
	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3668

3669
	p->reclaim_state = NULL;
3670
	fs_reclaim_release(sc.gfp_mask);
3671
	memalloc_noreclaim_restore(noreclaim_flag);
3672

3673
	return nr_reclaimed;
L
Linus Torvalds 已提交
3674
}
3675
#endif /* CONFIG_HIBERNATION */
L
Linus Torvalds 已提交
3676 3677 3678 3679 3680

/* 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. */
3681
static int kswapd_cpu_online(unsigned int cpu)
L
Linus Torvalds 已提交
3682
{
3683
	int nid;
L
Linus Torvalds 已提交
3684

3685 3686 3687
	for_each_node_state(nid, N_MEMORY) {
		pg_data_t *pgdat = NODE_DATA(nid);
		const struct cpumask *mask;
3688

3689
		mask = cpumask_of_node(pgdat->node_id);
3690

3691 3692 3693
		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);
L
Linus Torvalds 已提交
3694
	}
3695
	return 0;
L
Linus Torvalds 已提交
3696 3697
}

3698 3699 3700 3701 3702 3703 3704 3705 3706 3707 3708 3709 3710 3711 3712
/*
 * 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 */
3713
		BUG_ON(system_state < SYSTEM_RUNNING);
3714 3715
		pr_err("Failed to start kswapd on node %d\n", nid);
		ret = PTR_ERR(pgdat->kswapd);
3716
		pgdat->kswapd = NULL;
3717 3718 3719 3720
	}
	return ret;
}

3721
/*
3722
 * Called by memory hotplug when all memory in a node is offlined.  Caller must
3723
 * hold mem_hotplug_begin/end().
3724 3725 3726 3727 3728
 */
void kswapd_stop(int nid)
{
	struct task_struct *kswapd = NODE_DATA(nid)->kswapd;

3729
	if (kswapd) {
3730
		kthread_stop(kswapd);
3731 3732
		NODE_DATA(nid)->kswapd = NULL;
	}
3733 3734
}

L
Linus Torvalds 已提交
3735 3736
static int __init kswapd_init(void)
{
3737
	int nid, ret;
3738

L
Linus Torvalds 已提交
3739
	swap_setup();
3740
	for_each_node_state(nid, N_MEMORY)
3741
 		kswapd_run(nid);
3742 3743 3744 3745
	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
					"mm/vmscan:online", kswapd_cpu_online,
					NULL);
	WARN_ON(ret < 0);
L
Linus Torvalds 已提交
3746 3747 3748 3749
	return 0;
}

module_init(kswapd_init)
3750 3751 3752

#ifdef CONFIG_NUMA
/*
3753
 * Node reclaim mode
3754
 *
3755
 * If non-zero call node_reclaim when the number of free pages falls below
3756 3757
 * the watermarks.
 */
3758
int node_reclaim_mode __read_mostly;
3759

3760
#define RECLAIM_OFF 0
3761
#define RECLAIM_ZONE (1<<0)	/* Run shrink_inactive_list on the zone */
3762
#define RECLAIM_WRITE (1<<1)	/* Writeout pages during reclaim */
3763
#define RECLAIM_UNMAP (1<<2)	/* Unmap pages during reclaim */
3764

3765
/*
3766
 * Priority for NODE_RECLAIM. This determines the fraction of pages
3767 3768 3769
 * of a node considered for each zone_reclaim. 4 scans 1/16th of
 * a zone.
 */
3770
#define NODE_RECLAIM_PRIORITY 4
3771

3772
/*
3773
 * Percentage of pages in a zone that must be unmapped for node_reclaim to
3774 3775 3776 3777
 * occur.
 */
int sysctl_min_unmapped_ratio = 1;

3778 3779 3780 3781 3782 3783
/*
 * 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;

3784
static inline unsigned long node_unmapped_file_pages(struct pglist_data *pgdat)
3785
{
3786 3787 3788
	unsigned long file_mapped = node_page_state(pgdat, NR_FILE_MAPPED);
	unsigned long file_lru = node_page_state(pgdat, NR_INACTIVE_FILE) +
		node_page_state(pgdat, NR_ACTIVE_FILE);
3789 3790 3791 3792 3793 3794 3795 3796 3797 3798

	/*
	 * 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 */
3799
static unsigned long node_pagecache_reclaimable(struct pglist_data *pgdat)
3800
{
3801 3802
	unsigned long nr_pagecache_reclaimable;
	unsigned long delta = 0;
3803 3804

	/*
3805
	 * If RECLAIM_UNMAP is set, then all file pages are considered
3806
	 * potentially reclaimable. Otherwise, we have to worry about
3807
	 * pages like swapcache and node_unmapped_file_pages() provides
3808 3809
	 * a better estimate
	 */
3810 3811
	if (node_reclaim_mode & RECLAIM_UNMAP)
		nr_pagecache_reclaimable = node_page_state(pgdat, NR_FILE_PAGES);
3812
	else
3813
		nr_pagecache_reclaimable = node_unmapped_file_pages(pgdat);
3814 3815

	/* If we can't clean pages, remove dirty pages from consideration */
3816 3817
	if (!(node_reclaim_mode & RECLAIM_WRITE))
		delta += node_page_state(pgdat, NR_FILE_DIRTY);
3818 3819 3820 3821 3822 3823 3824 3825

	/* Watch for any possible underflows due to delta */
	if (unlikely(delta > nr_pagecache_reclaimable))
		delta = nr_pagecache_reclaimable;

	return nr_pagecache_reclaimable - delta;
}

3826
/*
3827
 * Try to free up some pages from this node through reclaim.
3828
 */
3829
static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
3830
{
3831
	/* Minimum pages needed in order to stay on node */
3832
	const unsigned long nr_pages = 1 << order;
3833 3834
	struct task_struct *p = current;
	struct reclaim_state reclaim_state;
3835
	unsigned int noreclaim_flag;
3836
	struct scan_control sc = {
3837
		.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3838
		.gfp_mask = current_gfp_context(gfp_mask),
3839
		.order = order,
3840 3841 3842
		.priority = NODE_RECLAIM_PRIORITY,
		.may_writepage = !!(node_reclaim_mode & RECLAIM_WRITE),
		.may_unmap = !!(node_reclaim_mode & RECLAIM_UNMAP),
3843
		.may_swap = 1,
3844
		.reclaim_idx = gfp_zone(gfp_mask),
3845
	};
3846 3847

	cond_resched();
3848
	/*
3849
	 * We need to be able to allocate from the reserves for RECLAIM_UNMAP
3850
	 * and we also need to be able to write out pages for RECLAIM_WRITE
3851
	 * and RECLAIM_UNMAP.
3852
	 */
3853 3854
	noreclaim_flag = memalloc_noreclaim_save();
	p->flags |= PF_SWAPWRITE;
3855
	fs_reclaim_acquire(sc.gfp_mask);
3856 3857
	reclaim_state.reclaimed_slab = 0;
	p->reclaim_state = &reclaim_state;
3858

3859
	if (node_pagecache_reclaimable(pgdat) > pgdat->min_unmapped_pages) {
3860 3861 3862 3863 3864
		/*
		 * Free memory by calling shrink zone with increasing
		 * priorities until we have enough memory freed.
		 */
		do {
3865
			shrink_node(pgdat, &sc);
3866
		} while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
3867
	}
3868

3869
	p->reclaim_state = NULL;
3870
	fs_reclaim_release(gfp_mask);
3871 3872
	current->flags &= ~PF_SWAPWRITE;
	memalloc_noreclaim_restore(noreclaim_flag);
3873
	return sc.nr_reclaimed >= nr_pages;
3874
}
3875

3876
int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
3877
{
3878
	int ret;
3879 3880

	/*
3881
	 * Node reclaim reclaims unmapped file backed pages and
3882
	 * slab pages if we are over the defined limits.
3883
	 *
3884 3885
	 * A small portion of unmapped file backed pages is needed for
	 * file I/O otherwise pages read by file I/O will be immediately
3886 3887
	 * thrown out if the node is overallocated. So we do not reclaim
	 * if less than a specified percentage of the node is used by
3888
	 * unmapped file backed pages.
3889
	 */
3890
	if (node_pagecache_reclaimable(pgdat) <= pgdat->min_unmapped_pages &&
3891
	    node_page_state(pgdat, NR_SLAB_RECLAIMABLE) <= pgdat->min_slab_pages)
3892
		return NODE_RECLAIM_FULL;
3893 3894

	/*
3895
	 * Do not scan if the allocation should not be delayed.
3896
	 */
3897
	if (!gfpflags_allow_blocking(gfp_mask) || (current->flags & PF_MEMALLOC))
3898
		return NODE_RECLAIM_NOSCAN;
3899 3900

	/*
3901
	 * Only run node reclaim on the local node or on nodes that do not
3902 3903 3904 3905
	 * have associated processors. This will favor the local processor
	 * over remote processors and spread off node memory allocations
	 * as wide as possible.
	 */
3906 3907
	if (node_state(pgdat->node_id, N_CPU) && pgdat->node_id != numa_node_id())
		return NODE_RECLAIM_NOSCAN;
3908

3909 3910
	if (test_and_set_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags))
		return NODE_RECLAIM_NOSCAN;
3911

3912 3913
	ret = __node_reclaim(pgdat, gfp_mask, order);
	clear_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags);
3914

3915 3916 3917
	if (!ret)
		count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);

3918
	return ret;
3919
}
3920
#endif
L
Lee Schermerhorn 已提交
3921 3922 3923 3924 3925 3926

/*
 * 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
3927
 * lists vs unevictable list.
L
Lee Schermerhorn 已提交
3928 3929
 *
 * Reasons page might not be evictable:
3930
 * (1) page's mapping marked unevictable
N
Nick Piggin 已提交
3931
 * (2) page is part of an mlocked VMA
3932
 *
L
Lee Schermerhorn 已提交
3933
 */
3934
int page_evictable(struct page *page)
L
Lee Schermerhorn 已提交
3935
{
3936
	return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
L
Lee Schermerhorn 已提交
3937
}
3938

3939
#ifdef CONFIG_SHMEM
3940
/**
3941 3942 3943
 * 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
3944
 *
3945
 * Checks pages for evictability and moves them to the appropriate lru list.
3946 3947
 *
 * This function is only used for SysV IPC SHM_UNLOCK.
3948
 */
3949
void check_move_unevictable_pages(struct page **pages, int nr_pages)
3950
{
3951
	struct lruvec *lruvec;
3952
	struct pglist_data *pgdat = NULL;
3953 3954 3955
	int pgscanned = 0;
	int pgrescued = 0;
	int i;
3956

3957 3958
	for (i = 0; i < nr_pages; i++) {
		struct page *page = pages[i];
3959
		struct pglist_data *pagepgdat = page_pgdat(page);
3960

3961
		pgscanned++;
3962 3963 3964 3965 3966
		if (pagepgdat != pgdat) {
			if (pgdat)
				spin_unlock_irq(&pgdat->lru_lock);
			pgdat = pagepgdat;
			spin_lock_irq(&pgdat->lru_lock);
3967
		}
3968
		lruvec = mem_cgroup_page_lruvec(page, pgdat);
3969

3970 3971
		if (!PageLRU(page) || !PageUnevictable(page))
			continue;
3972

3973
		if (page_evictable(page)) {
3974 3975
			enum lru_list lru = page_lru_base_type(page);

3976
			VM_BUG_ON_PAGE(PageActive(page), page);
3977
			ClearPageUnevictable(page);
3978 3979
			del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
			add_page_to_lru_list(page, lruvec, lru);
3980
			pgrescued++;
3981
		}
3982
	}
3983

3984
	if (pgdat) {
3985 3986
		__count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
		__count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
3987
		spin_unlock_irq(&pgdat->lru_lock);
3988 3989
	}
}
3990
#endif /* CONFIG_SHMEM */