vmscan.c 119.3 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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	/*
	 * 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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	/* 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;

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	/* Allocation order */
	s8 order;

	/* Scan (total_size >> priority) pages at once */
	s8 priority;

	/* The highest zone to isolate pages for reclaim from */
	s8 reclaim_idx;

	/* This context's GFP mask */
	gfp_t gfp_mask;

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	/* 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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	struct {
		unsigned int dirty;
		unsigned int unqueued_dirty;
		unsigned int congested;
		unsigned int writeback;
		unsigned int immediate;
		unsigned int file_taken;
		unsigned int taken;
	} nr;
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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_KMEM
static DEFINE_IDR(shrinker_idr);
static int shrinker_nr_max;

static int prealloc_memcg_shrinker(struct shrinker *shrinker)
{
	int id, ret = -ENOMEM;

	down_write(&shrinker_rwsem);
	/* This may call shrinker, so it must use down_read_trylock() */
	id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
	if (id < 0)
		goto unlock;

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	if (id >= shrinker_nr_max) {
		if (memcg_expand_shrinker_maps(id)) {
			idr_remove(&shrinker_idr, id);
			goto unlock;
		}

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		shrinker_nr_max = id + 1;
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	}
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	shrinker->id = id;
	ret = 0;
unlock:
	up_write(&shrinker_rwsem);
	return ret;
}

static void unregister_memcg_shrinker(struct shrinker *shrinker)
{
	int id = shrinker->id;

	BUG_ON(id < 0);

	down_write(&shrinker_rwsem);
	idr_remove(&shrinker_idr, id);
	up_write(&shrinker_rwsem);
}
#else /* CONFIG_MEMCG_KMEM */
static int prealloc_memcg_shrinker(struct shrinker *shrinker)
{
	return 0;
}

static void unregister_memcg_shrinker(struct shrinker *shrinker)
{
}
#endif /* CONFIG_MEMCG_KMEM */

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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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static void set_memcg_congestion(pg_data_t *pgdat,
				struct mem_cgroup *memcg,
				bool congested)
{
	struct mem_cgroup_per_node *mn;

	if (!memcg)
		return;

	mn = mem_cgroup_nodeinfo(memcg, pgdat->node_id);
	WRITE_ONCE(mn->congested, congested);
}

static bool memcg_congested(pg_data_t *pgdat,
			struct mem_cgroup *memcg)
{
	struct mem_cgroup_per_node *mn;

	mn = mem_cgroup_nodeinfo(memcg, pgdat->node_id);
	return READ_ONCE(mn->congested);

}
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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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static inline void set_memcg_congestion(struct pglist_data *pgdat,
				struct mem_cgroup *memcg, bool congested)
{
}

static inline bool memcg_congested(struct pglist_data *pgdat,
			struct mem_cgroup *memcg)
{
	return false;

}
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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 prealloc_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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	/*
	 * There is a window between prealloc_shrinker()
	 * and register_shrinker_prepared(). We don't want
	 * to clear bit of a shrinker in such the state
	 * in shrink_slab_memcg(), since this will impose
	 * restrictions on a code registering a shrinker
	 * (they would have to guarantee, their LRU lists
	 * are empty till shrinker is completely registered).
	 * So, we differ the situation, when 1)a shrinker
	 * is semi-registered (id is assigned, but it has
	 * not yet linked to shrinker_list) and 2)shrinker
	 * is not registered (id is not assigned).
	 */
	INIT_LIST_HEAD(&shrinker->list);

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	if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
		if (prealloc_memcg_shrinker(shrinker))
			goto free_deferred;
	}

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	return 0;
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free_deferred:
	kfree(shrinker->nr_deferred);
	shrinker->nr_deferred = NULL;
	return -ENOMEM;
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}

void free_prealloced_shrinker(struct shrinker *shrinker)
{
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	if (!shrinker->nr_deferred)
		return;

	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
		unregister_memcg_shrinker(shrinker);

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	kfree(shrinker->nr_deferred);
	shrinker->nr_deferred = NULL;
}
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void register_shrinker_prepared(struct shrinker *shrinker)
{
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	down_write(&shrinker_rwsem);
	list_add_tail(&shrinker->list, &shrinker_list);
	up_write(&shrinker_rwsem);
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}

int register_shrinker(struct shrinker *shrinker)
{
	int err = prealloc_shrinker(shrinker);

	if (err)
		return err;
	register_shrinker_prepared(shrinker);
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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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	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
		unregister_memcg_shrinker(shrinker);
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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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#ifdef CONFIG_MEMCG_KMEM
static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
			struct mem_cgroup *memcg, int priority)
{
	struct memcg_shrinker_map *map;
	unsigned long freed = 0;
	int ret, i;

	if (!memcg_kmem_enabled() || !mem_cgroup_online(memcg))
		return 0;

	if (!down_read_trylock(&shrinker_rwsem))
		return 0;

	map = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_map,
					true);
	if (unlikely(!map))
		goto unlock;

	for_each_set_bit(i, map->map, shrinker_nr_max) {
		struct shrink_control sc = {
			.gfp_mask = gfp_mask,
			.nid = nid,
			.memcg = memcg,
		};
		struct shrinker *shrinker;

		shrinker = idr_find(&shrinker_idr, i);
		if (unlikely(!shrinker)) {
			clear_bit(i, map->map);
			continue;
		}

		/* See comment in prealloc_shrinker() */
		if (unlikely(list_empty(&shrinker->list)))
			continue;

		ret = do_shrink_slab(&sc, shrinker, priority);
		freed += ret;

		if (rwsem_is_contended(&shrinker_rwsem)) {
			freed = freed ? : 1;
			break;
		}
	}
unlock:
	up_read(&shrinker_rwsem);
	return freed;
}
#else /* CONFIG_MEMCG_KMEM */
static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
			struct mem_cgroup *memcg, int priority)
{
	return 0;
}
#endif /* CONFIG_MEMCG_KMEM */

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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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 */
640 641
static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
				 struct mem_cgroup *memcg,
642
				 int priority)
L
Linus Torvalds 已提交
643 644
{
	struct shrinker *shrinker;
D
Dave Chinner 已提交
645
	unsigned long freed = 0;
L
Linus Torvalds 已提交
646

647 648
	if (memcg && !mem_cgroup_is_root(memcg))
		return shrink_slab_memcg(gfp_mask, nid, memcg, priority);
649

650
	if (!down_read_trylock(&shrinker_rwsem))
651
		goto out;
L
Linus Torvalds 已提交
652 653

	list_for_each_entry(shrinker, &shrinker_list, list) {
654 655 656
		struct shrink_control sc = {
			.gfp_mask = gfp_mask,
			.nid = nid,
657
			.memcg = memcg,
658
		};
659

660
		if (!!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE))
661 662
			continue;

663 664
		if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
			sc.nid = 0;
L
Linus Torvalds 已提交
665

666
		freed += do_shrink_slab(&sc, shrinker, priority);
667 668 669 670 671 672 673 674 675
		/*
		 * 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;
		}
L
Linus Torvalds 已提交
676
	}
677

L
Linus Torvalds 已提交
678
	up_read(&shrinker_rwsem);
679 680
out:
	cond_resched();
D
Dave Chinner 已提交
681
	return freed;
L
Linus Torvalds 已提交
682 683
}

684 685 686 687 688 689 690 691 692
void drop_slab_node(int nid)
{
	unsigned long freed;

	do {
		struct mem_cgroup *memcg = NULL;

		freed = 0;
		do {
693
			freed += shrink_slab(GFP_KERNEL, nid, memcg, 0);
694 695 696 697 698 699 700 701 702 703 704 705
		} 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);
}

L
Linus Torvalds 已提交
706 707
static inline int is_page_cache_freeable(struct page *page)
{
708 709 710 711 712
	/*
	 * 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.
	 */
713 714 715
	int radix_pins = PageTransHuge(page) && PageSwapCache(page) ?
		HPAGE_PMD_NR : 1;
	return page_count(page) - page_has_private(page) == 1 + radix_pins;
L
Linus Torvalds 已提交
716 717
}

718
static int may_write_to_inode(struct inode *inode, struct scan_control *sc)
L
Linus Torvalds 已提交
719
{
720
	if (current->flags & PF_SWAPWRITE)
L
Linus Torvalds 已提交
721
		return 1;
722
	if (!inode_write_congested(inode))
L
Linus Torvalds 已提交
723
		return 1;
724
	if (inode_to_bdi(inode) == current->backing_dev_info)
L
Linus Torvalds 已提交
725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743
		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)
{
J
Jens Axboe 已提交
744
	lock_page(page);
745 746
	if (page_mapping(page) == mapping)
		mapping_set_error(mapping, error);
L
Linus Torvalds 已提交
747 748 749
	unlock_page(page);
}

750 751 752 753 754 755 756 757 758 759 760 761
/* 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;

L
Linus Torvalds 已提交
762
/*
A
Andrew Morton 已提交
763 764
 * pageout is called by shrink_page_list() for each dirty page.
 * Calls ->writepage().
L
Linus Torvalds 已提交
765
 */
766
static pageout_t pageout(struct page *page, struct address_space *mapping,
767
			 struct scan_control *sc)
L
Linus Torvalds 已提交
768 769 770 771 772 773 774 775
{
	/*
	 * 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.
	 *
776
	 * If this process is currently in __generic_file_write_iter() against
L
Linus Torvalds 已提交
777 778 779 780 781 782 783 784 785 786 787 788 789 790 791
	 * 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.
		 */
792
		if (page_has_private(page)) {
L
Linus Torvalds 已提交
793 794
			if (try_to_free_buffers(page)) {
				ClearPageDirty(page);
795
				pr_info("%s: orphaned page\n", __func__);
L
Linus Torvalds 已提交
796 797 798 799 800 801 802
				return PAGE_CLEAN;
			}
		}
		return PAGE_KEEP;
	}
	if (mapping->a_ops->writepage == NULL)
		return PAGE_ACTIVATE;
803
	if (!may_write_to_inode(mapping->host, sc))
L
Linus Torvalds 已提交
804 805 806 807 808 809 810
		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,
811 812
			.range_start = 0,
			.range_end = LLONG_MAX,
L
Linus Torvalds 已提交
813 814 815 816 817 818 819
			.for_reclaim = 1,
		};

		SetPageReclaim(page);
		res = mapping->a_ops->writepage(page, &wbc);
		if (res < 0)
			handle_write_error(mapping, page, res);
820
		if (res == AOP_WRITEPAGE_ACTIVATE) {
L
Linus Torvalds 已提交
821 822 823
			ClearPageReclaim(page);
			return PAGE_ACTIVATE;
		}
824

L
Linus Torvalds 已提交
825 826 827 828
		if (!PageWriteback(page)) {
			/* synchronous write or broken a_ops? */
			ClearPageReclaim(page);
		}
829
		trace_mm_vmscan_writepage(page);
830
		inc_node_page_state(page, NR_VMSCAN_WRITE);
L
Linus Torvalds 已提交
831 832 833 834 835 836
		return PAGE_SUCCESS;
	}

	return PAGE_CLEAN;
}

837
/*
N
Nick Piggin 已提交
838 839
 * Same as remove_mapping, but if the page is removed from the mapping, it
 * gets returned with a refcount of 0.
840
 */
841 842
static int __remove_mapping(struct address_space *mapping, struct page *page,
			    bool reclaimed)
843
{
844
	unsigned long flags;
845
	int refcount;
846

847 848
	BUG_ON(!PageLocked(page));
	BUG_ON(mapping != page_mapping(page));
849

M
Matthew Wilcox 已提交
850
	xa_lock_irqsave(&mapping->i_pages, flags);
851
	/*
N
Nick Piggin 已提交
852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870
	 * 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
871
	 * load is not satisfied before that of page->_refcount.
N
Nick Piggin 已提交
872 873
	 *
	 * Note that if SetPageDirty is always performed via set_page_dirty,
M
Matthew Wilcox 已提交
874
	 * and thus under the i_pages lock, then this ordering is not required.
875
	 */
876 877 878 879 880
	if (unlikely(PageTransHuge(page)) && PageSwapCache(page))
		refcount = 1 + HPAGE_PMD_NR;
	else
		refcount = 2;
	if (!page_ref_freeze(page, refcount))
881
		goto cannot_free;
N
Nick Piggin 已提交
882 883
	/* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
	if (unlikely(PageDirty(page))) {
884
		page_ref_unfreeze(page, refcount);
885
		goto cannot_free;
N
Nick Piggin 已提交
886
	}
887 888 889

	if (PageSwapCache(page)) {
		swp_entry_t swap = { .val = page_private(page) };
890
		mem_cgroup_swapout(page, swap);
891
		__delete_from_swap_cache(page);
M
Matthew Wilcox 已提交
892
		xa_unlock_irqrestore(&mapping->i_pages, flags);
893
		put_swap_page(page, swap);
N
Nick Piggin 已提交
894
	} else {
895
		void (*freepage)(struct page *);
896
		void *shadow = NULL;
897 898

		freepage = mapping->a_ops->freepage;
899 900 901 902 903 904 905 906 907
		/*
		 * 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.
908 909 910 911 912
		 *
		 * 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
M
Matthew Wilcox 已提交
913
		 * same address_space.
914 915
		 */
		if (reclaimed && page_is_file_cache(page) &&
916
		    !mapping_exiting(mapping) && !dax_mapping(mapping))
917
			shadow = workingset_eviction(mapping, page);
J
Johannes Weiner 已提交
918
		__delete_from_page_cache(page, shadow);
M
Matthew Wilcox 已提交
919
		xa_unlock_irqrestore(&mapping->i_pages, flags);
920 921 922

		if (freepage != NULL)
			freepage(page);
923 924 925 926 927
	}

	return 1;

cannot_free:
M
Matthew Wilcox 已提交
928
	xa_unlock_irqrestore(&mapping->i_pages, flags);
929 930 931
	return 0;
}

N
Nick Piggin 已提交
932 933 934 935 936 937 938 939
/*
 * 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)
{
940
	if (__remove_mapping(mapping, page, false)) {
N
Nick Piggin 已提交
941 942 943 944 945
		/*
		 * Unfreezing the refcount with 1 rather than 2 effectively
		 * drops the pagecache ref for us without requiring another
		 * atomic operation.
		 */
946
		page_ref_unfreeze(page, 1);
N
Nick Piggin 已提交
947 948 949 950 951
		return 1;
	}
	return 0;
}

L
Lee Schermerhorn 已提交
952 953 954 955 956 957 958 959 960 961 962
/**
 * 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)
{
963
	lru_cache_add(page);
L
Lee Schermerhorn 已提交
964 965 966
	put_page(page);		/* drop ref from isolate */
}

967 968 969
enum page_references {
	PAGEREF_RECLAIM,
	PAGEREF_RECLAIM_CLEAN,
970
	PAGEREF_KEEP,
971 972 973 974 975 976
	PAGEREF_ACTIVATE,
};

static enum page_references page_check_references(struct page *page,
						  struct scan_control *sc)
{
977
	int referenced_ptes, referenced_page;
978 979
	unsigned long vm_flags;

980 981
	referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
					  &vm_flags);
982
	referenced_page = TestClearPageReferenced(page);
983 984 985 986 987 988 989 990

	/*
	 * 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;

991
	if (referenced_ptes) {
992
		if (PageSwapBacked(page))
993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009
			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);

1010
		if (referenced_page || referenced_ptes > 1)
1011 1012
			return PAGEREF_ACTIVATE;

1013 1014 1015 1016 1017 1018
		/*
		 * Activate file-backed executable pages after first usage.
		 */
		if (vm_flags & VM_EXEC)
			return PAGEREF_ACTIVATE;

1019 1020
		return PAGEREF_KEEP;
	}
1021 1022

	/* Reclaim if clean, defer dirty pages to writeback */
1023
	if (referenced_page && !PageSwapBacked(page))
1024 1025 1026
		return PAGEREF_RECLAIM_CLEAN;

	return PAGEREF_RECLAIM;
1027 1028
}

1029 1030 1031 1032
/* Check if a page is dirty or under writeback */
static void page_check_dirty_writeback(struct page *page,
				       bool *dirty, bool *writeback)
{
1033 1034
	struct address_space *mapping;

1035 1036 1037 1038
	/*
	 * 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
1039 1040
	if (!page_is_file_cache(page) ||
	    (PageAnon(page) && !PageSwapBacked(page))) {
1041 1042 1043 1044 1045 1046 1047 1048
		*dirty = false;
		*writeback = false;
		return;
	}

	/* By default assume that the page flags are accurate */
	*dirty = PageDirty(page);
	*writeback = PageWriteback(page);
1049 1050 1051 1052 1053 1054 1055 1056

	/* 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);
1057 1058
}

L
Linus Torvalds 已提交
1059
/*
A
Andrew Morton 已提交
1060
 * shrink_page_list() returns the number of reclaimed pages
L
Linus Torvalds 已提交
1061
 */
A
Andrew Morton 已提交
1062
static unsigned long shrink_page_list(struct list_head *page_list,
M
Mel Gorman 已提交
1063
				      struct pglist_data *pgdat,
1064
				      struct scan_control *sc,
1065
				      enum ttu_flags ttu_flags,
1066
				      struct reclaim_stat *stat,
1067
				      bool force_reclaim)
L
Linus Torvalds 已提交
1068 1069
{
	LIST_HEAD(ret_pages);
1070
	LIST_HEAD(free_pages);
L
Linus Torvalds 已提交
1071
	int pgactivate = 0;
1072 1073 1074 1075 1076 1077
	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;
1078 1079
	unsigned nr_ref_keep = 0;
	unsigned nr_unmap_fail = 0;
L
Linus Torvalds 已提交
1080 1081 1082 1083 1084 1085 1086

	cond_resched();

	while (!list_empty(page_list)) {
		struct address_space *mapping;
		struct page *page;
		int may_enter_fs;
1087
		enum page_references references = PAGEREF_RECLAIM_CLEAN;
1088
		bool dirty, writeback;
L
Linus Torvalds 已提交
1089 1090 1091 1092 1093 1094

		cond_resched();

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

N
Nick Piggin 已提交
1095
		if (!trylock_page(page))
L
Linus Torvalds 已提交
1096 1097
			goto keep;

1098
		VM_BUG_ON_PAGE(PageActive(page), page);
L
Linus Torvalds 已提交
1099 1100

		sc->nr_scanned++;
1101

1102
		if (unlikely(!page_evictable(page)))
M
Minchan Kim 已提交
1103
			goto activate_locked;
L
Lee Schermerhorn 已提交
1104

1105
		if (!sc->may_unmap && page_mapped(page))
1106 1107
			goto keep_locked;

L
Linus Torvalds 已提交
1108
		/* Double the slab pressure for mapped and swapcache pages */
S
Shaohua Li 已提交
1109 1110
		if ((page_mapped(page) || PageSwapCache(page)) &&
		    !(PageAnon(page) && !PageSwapBacked(page)))
L
Linus Torvalds 已提交
1111 1112
			sc->nr_scanned++;

1113 1114 1115
		may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
			(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));

1116
		/*
1117
		 * The number of dirty pages determines if a node is marked
1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128
		 * 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++;

1129 1130 1131 1132 1133 1134
		/*
		 * 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.
		 */
1135
		mapping = page_mapping(page);
1136
		if (((dirty || writeback) && mapping &&
1137
		     inode_write_congested(mapping->host)) ||
1138
		    (writeback && PageReclaim(page)))
1139 1140
			nr_congested++;

1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151
		/*
		 * 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
1152 1153
		 *    note that the LRU is being scanned too quickly and the
		 *    caller can stall after page list has been processed.
1154
		 *
1155
		 * 2) Global or new memcg reclaim encounters a page that is
1156 1157 1158
		 *    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
1159
		 *    reclaim and continue scanning.
1160
		 *
1161 1162
		 *    Require may_enter_fs because we would wait on fs, which
		 *    may not have submitted IO yet. And the loop driver might
1163 1164 1165 1166 1167
		 *    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.
		 *
1168
		 * 3) Legacy memcg encounters a page that is already marked
1169 1170 1171 1172
		 *    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.
1173 1174 1175 1176 1177 1178 1179 1180 1181
		 *
		 * 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.
1182
		 */
1183
		if (PageWriteback(page)) {
1184 1185 1186
			/* Case 1 above */
			if (current_is_kswapd() &&
			    PageReclaim(page) &&
M
Mel Gorman 已提交
1187
			    test_bit(PGDAT_WRITEBACK, &pgdat->flags)) {
1188
				nr_immediate++;
1189
				goto activate_locked;
1190 1191

			/* Case 2 above */
1192
			} else if (sane_reclaim(sc) ||
1193
			    !PageReclaim(page) || !may_enter_fs) {
1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205
				/*
				 * 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);
1206
				nr_writeback++;
1207
				goto activate_locked;
1208 1209 1210

			/* Case 3 above */
			} else {
1211
				unlock_page(page);
1212
				wait_on_page_writeback(page);
1213 1214 1215
				/* then go back and try same page again */
				list_add_tail(&page->lru, page_list);
				continue;
1216
			}
1217
		}
L
Linus Torvalds 已提交
1218

1219 1220 1221
		if (!force_reclaim)
			references = page_check_references(page, sc);

1222 1223
		switch (references) {
		case PAGEREF_ACTIVATE:
L
Linus Torvalds 已提交
1224
			goto activate_locked;
1225
		case PAGEREF_KEEP:
1226
			nr_ref_keep++;
1227
			goto keep_locked;
1228 1229 1230 1231
		case PAGEREF_RECLAIM:
		case PAGEREF_RECLAIM_CLEAN:
			; /* try to reclaim the page below */
		}
L
Linus Torvalds 已提交
1232 1233 1234 1235

		/*
		 * Anonymous process memory has backing store?
		 * Try to allocate it some swap space here.
S
Shaohua Li 已提交
1236
		 * Lazyfree page could be freed directly
L
Linus Torvalds 已提交
1237
		 */
1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262
		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;
1263 1264 1265
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
					count_vm_event(THP_SWPOUT_FALLBACK);
#endif
1266 1267 1268
					if (!add_to_swap(page))
						goto activate_locked;
				}
1269

1270
				may_enter_fs = 1;
L
Linus Torvalds 已提交
1271

1272 1273 1274
				/* Adding to swap updated mapping */
				mapping = page_mapping(page);
			}
1275 1276 1277 1278
		} else if (unlikely(PageTransHuge(page))) {
			/* Split file THP */
			if (split_huge_page_to_list(page, page_list))
				goto keep_locked;
1279
		}
L
Linus Torvalds 已提交
1280 1281 1282 1283 1284

		/*
		 * The page is mapped into the page tables of one or more
		 * processes. Try to unmap it here.
		 */
S
Shaohua Li 已提交
1285
		if (page_mapped(page)) {
1286 1287 1288 1289 1290
			enum ttu_flags flags = ttu_flags | TTU_BATCH_FLUSH;

			if (unlikely(PageTransHuge(page)))
				flags |= TTU_SPLIT_HUGE_PMD;
			if (!try_to_unmap(page, flags)) {
1291
				nr_unmap_fail++;
L
Linus Torvalds 已提交
1292 1293 1294 1295 1296
				goto activate_locked;
			}
		}

		if (PageDirty(page)) {
1297
			/*
1298 1299 1300 1301 1302 1303 1304 1305
			 * 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).
1306
			 */
1307
			if (page_is_file_cache(page) &&
1308 1309
			    (!current_is_kswapd() || !PageReclaim(page) ||
			     !test_bit(PGDAT_DIRTY, &pgdat->flags))) {
1310 1311 1312 1313 1314 1315
				/*
				 * Immediately reclaim when written back.
				 * Similar in principal to deactivate_page()
				 * except we already have the page isolated
				 * and know it's dirty
				 */
1316
				inc_node_page_state(page, NR_VMSCAN_IMMEDIATE);
1317 1318
				SetPageReclaim(page);

1319
				goto activate_locked;
1320 1321
			}

1322
			if (references == PAGEREF_RECLAIM_CLEAN)
L
Linus Torvalds 已提交
1323
				goto keep_locked;
1324
			if (!may_enter_fs)
L
Linus Torvalds 已提交
1325
				goto keep_locked;
1326
			if (!sc->may_writepage)
L
Linus Torvalds 已提交
1327 1328
				goto keep_locked;

1329 1330 1331 1332 1333 1334
			/*
			 * 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();
1335
			switch (pageout(page, mapping, sc)) {
L
Linus Torvalds 已提交
1336 1337 1338 1339 1340
			case PAGE_KEEP:
				goto keep_locked;
			case PAGE_ACTIVATE:
				goto activate_locked;
			case PAGE_SUCCESS:
1341
				if (PageWriteback(page))
1342
					goto keep;
1343
				if (PageDirty(page))
L
Linus Torvalds 已提交
1344
					goto keep;
1345

L
Linus Torvalds 已提交
1346 1347 1348 1349
				/*
				 * A synchronous write - probably a ramdisk.  Go
				 * ahead and try to reclaim the page.
				 */
N
Nick Piggin 已提交
1350
				if (!trylock_page(page))
L
Linus Torvalds 已提交
1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369
					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
1370
		 * will do this, as well as the blockdev mapping.
L
Linus Torvalds 已提交
1371 1372 1373 1374 1375 1376 1377 1378 1379 1380
		 * 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.
		 */
1381
		if (page_has_private(page)) {
L
Linus Torvalds 已提交
1382 1383
			if (!try_to_release_page(page, sc->gfp_mask))
				goto activate_locked;
N
Nick Piggin 已提交
1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399
			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
1400 1401
		}

S
Shaohua Li 已提交
1402 1403 1404 1405 1406 1407 1408 1409
		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
1410

S
Shaohua Li 已提交
1411
			count_vm_event(PGLAZYFREED);
1412
			count_memcg_page_event(page, PGLAZYFREED);
S
Shaohua Li 已提交
1413 1414
		} else if (!mapping || !__remove_mapping(mapping, page, true))
			goto keep_locked;
N
Nick Piggin 已提交
1415 1416 1417 1418 1419 1420 1421
		/*
		 * 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.
		 */
1422
		__ClearPageLocked(page);
N
Nick Piggin 已提交
1423
free_it:
1424
		nr_reclaimed++;
1425 1426 1427 1428 1429

		/*
		 * Is there need to periodically free_page_list? It would
		 * appear not as the counts should be low
		 */
1430 1431 1432 1433 1434
		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
1435 1436 1437
		continue;

activate_locked:
1438
		/* Not a candidate for swapping, so reclaim swap space. */
M
Minchan Kim 已提交
1439 1440
		if (PageSwapCache(page) && (mem_cgroup_swap_full(page) ||
						PageMlocked(page)))
1441
			try_to_free_swap(page);
1442
		VM_BUG_ON_PAGE(PageActive(page), page);
M
Minchan Kim 已提交
1443 1444 1445
		if (!PageMlocked(page)) {
			SetPageActive(page);
			pgactivate++;
1446
			count_memcg_page_event(page, PGACTIVATE);
M
Minchan Kim 已提交
1447
		}
L
Linus Torvalds 已提交
1448 1449 1450 1451
keep_locked:
		unlock_page(page);
keep:
		list_add(&page->lru, &ret_pages);
1452
		VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page);
L
Linus Torvalds 已提交
1453
	}
1454

1455
	mem_cgroup_uncharge_list(&free_pages);
1456
	try_to_unmap_flush();
1457
	free_unref_page_list(&free_pages);
1458

L
Linus Torvalds 已提交
1459
	list_splice(&ret_pages, page_list);
1460
	count_vm_events(PGACTIVATE, pgactivate);
1461

1462 1463 1464 1465 1466 1467
	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;
1468 1469 1470
		stat->nr_activate = pgactivate;
		stat->nr_ref_keep = nr_ref_keep;
		stat->nr_unmap_fail = nr_unmap_fail;
1471
	}
1472
	return nr_reclaimed;
L
Linus Torvalds 已提交
1473 1474
}

1475 1476 1477 1478 1479 1480 1481 1482
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,
	};
1483
	unsigned long ret;
1484 1485 1486 1487
	struct page *page, *next;
	LIST_HEAD(clean_pages);

	list_for_each_entry_safe(page, next, page_list, lru) {
1488
		if (page_is_file_cache(page) && !PageDirty(page) &&
1489
		    !__PageMovable(page)) {
1490 1491 1492 1493 1494
			ClearPageActive(page);
			list_move(&page->lru, &clean_pages);
		}
	}

M
Mel Gorman 已提交
1495
	ret = shrink_page_list(&clean_pages, zone->zone_pgdat, &sc,
S
Shaohua Li 已提交
1496
			TTU_IGNORE_ACCESS, NULL, true);
1497
	list_splice(&clean_pages, page_list);
M
Mel Gorman 已提交
1498
	mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE, -ret);
1499 1500 1501
	return ret;
}

A
Andy Whitcroft 已提交
1502 1503 1504 1505 1506 1507 1508 1509 1510 1511
/*
 * 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.
 */
1512
int __isolate_lru_page(struct page *page, isolate_mode_t mode)
A
Andy Whitcroft 已提交
1513 1514 1515 1516 1517 1518 1519
{
	int ret = -EINVAL;

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

M
Minchan Kim 已提交
1520 1521
	/* Compaction should not handle unevictable pages but CMA can do so */
	if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
L
Lee Schermerhorn 已提交
1522 1523
		return ret;

A
Andy Whitcroft 已提交
1524
	ret = -EBUSY;
K
KAMEZAWA Hiroyuki 已提交
1525

1526 1527 1528 1529 1530 1531 1532 1533
	/*
	 * 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
	 */
1534
	if (mode & ISOLATE_ASYNC_MIGRATE) {
1535 1536 1537 1538 1539 1540
		/* All the caller can do on PageWriteback is block */
		if (PageWriteback(page))
			return ret;

		if (PageDirty(page)) {
			struct address_space *mapping;
1541
			bool migrate_dirty;
1542 1543 1544 1545

			/*
			 * Only pages without mappings or that have a
			 * ->migratepage callback are possible to migrate
1546 1547 1548 1549 1550
			 * 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.
1551
			 */
1552 1553 1554
			if (!trylock_page(page))
				return ret;

1555
			mapping = page_mapping(page);
1556
			migrate_dirty = !mapping || mapping->a_ops->migratepage;
1557 1558
			unlock_page(page);
			if (!migrate_dirty)
1559 1560 1561
				return ret;
		}
	}
1562

1563 1564 1565
	if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
		return ret;

A
Andy Whitcroft 已提交
1566 1567 1568 1569 1570 1571 1572 1573 1574 1575 1576 1577 1578
	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;
}

1579 1580 1581 1582 1583 1584

/*
 * 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,
1585
			enum lru_list lru, unsigned long *nr_zone_taken)
1586 1587 1588 1589 1590 1591 1592 1593 1594
{
	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
1595
		mem_cgroup_update_lru_size(lruvec, lru, zid, -nr_zone_taken[zid]);
1596
#endif
1597 1598
	}

1599 1600
}

L
Linus Torvalds 已提交
1601
/*
1602
 * zone_lru_lock is heavily contended.  Some of the functions that
L
Linus Torvalds 已提交
1603 1604 1605 1606 1607 1608 1609 1610
 * 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.
 *
1611
 * @nr_to_scan:	The number of eligible pages to look through on the list.
1612
 * @lruvec:	The LRU vector to pull pages from.
L
Linus Torvalds 已提交
1613
 * @dst:	The temp list to put pages on to.
H
Hugh Dickins 已提交
1614
 * @nr_scanned:	The number of pages that were scanned.
1615
 * @sc:		The scan_control struct for this reclaim session
A
Andy Whitcroft 已提交
1616
 * @mode:	One of the LRU isolation modes
1617
 * @lru:	LRU list id for isolating
L
Linus Torvalds 已提交
1618 1619 1620
 *
 * returns how many pages were moved onto *@dst.
 */
1621
static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1622
		struct lruvec *lruvec, struct list_head *dst,
1623
		unsigned long *nr_scanned, struct scan_control *sc,
1624
		isolate_mode_t mode, enum lru_list lru)
L
Linus Torvalds 已提交
1625
{
H
Hugh Dickins 已提交
1626
	struct list_head *src = &lruvec->lists[lru];
1627
	unsigned long nr_taken = 0;
M
Mel Gorman 已提交
1628
	unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 };
1629
	unsigned long nr_skipped[MAX_NR_ZONES] = { 0, };
1630
	unsigned long skipped = 0;
1631
	unsigned long scan, total_scan, nr_pages;
1632
	LIST_HEAD(pages_skipped);
L
Linus Torvalds 已提交
1633

1634 1635 1636 1637
	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
1638 1639
		struct page *page;

L
Linus Torvalds 已提交
1640 1641 1642
		page = lru_to_page(src);
		prefetchw_prev_lru_page(page, src, flags);

1643
		VM_BUG_ON_PAGE(!PageLRU(page), page);
N
Nick Piggin 已提交
1644

1645 1646
		if (page_zonenum(page) > sc->reclaim_idx) {
			list_move(&page->lru, &pages_skipped);
1647
			nr_skipped[page_zonenum(page)]++;
1648 1649 1650
			continue;
		}

1651 1652 1653 1654 1655 1656 1657
		/*
		 * 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++;
1658
		switch (__isolate_lru_page(page, mode)) {
A
Andy Whitcroft 已提交
1659
		case 0:
M
Mel Gorman 已提交
1660 1661 1662
			nr_pages = hpage_nr_pages(page);
			nr_taken += nr_pages;
			nr_zone_taken[page_zonenum(page)] += nr_pages;
A
Andy Whitcroft 已提交
1663 1664 1665 1666 1667 1668 1669
			list_move(&page->lru, dst);
			break;

		case -EBUSY:
			/* else it is being freed elsewhere */
			list_move(&page->lru, src);
			continue;
1670

A
Andy Whitcroft 已提交
1671 1672 1673
		default:
			BUG();
		}
L
Linus Torvalds 已提交
1674 1675
	}

1676 1677 1678 1679 1680 1681 1682
	/*
	 * 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.
	 */
1683 1684 1685
	if (!list_empty(&pages_skipped)) {
		int zid;

1686
		list_splice(&pages_skipped, src);
1687 1688 1689 1690 1691
		for (zid = 0; zid < MAX_NR_ZONES; zid++) {
			if (!nr_skipped[zid])
				continue;

			__count_zid_vm_events(PGSCAN_SKIP, zid, nr_skipped[zid]);
1692
			skipped += nr_skipped[zid];
1693 1694
		}
	}
1695
	*nr_scanned = total_scan;
1696
	trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan,
1697
				    total_scan, skipped, nr_taken, mode, lru);
1698
	update_lru_sizes(lruvec, lru, nr_zone_taken);
L
Linus Torvalds 已提交
1699 1700 1701
	return nr_taken;
}

1702 1703 1704 1705 1706 1707 1708 1709 1710 1711 1712
/**
 * 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
1713 1714 1715
 * 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.
1716 1717 1718 1719 1720
 *
 * The vmstat statistic corresponding to the list on which the page was
 * found will be decremented.
 *
 * Restrictions:
1721
 *
1722 1723 1724 1725 1726 1727 1728 1729 1730 1731
 * (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;

1732
	VM_BUG_ON_PAGE(!page_count(page), page);
1733
	WARN_RATELIMIT(PageTail(page), "trying to isolate tail page");
1734

1735 1736
	if (PageLRU(page)) {
		struct zone *zone = page_zone(page);
1737
		struct lruvec *lruvec;
1738

1739
		spin_lock_irq(zone_lru_lock(zone));
M
Mel Gorman 已提交
1740
		lruvec = mem_cgroup_page_lruvec(page, zone->zone_pgdat);
1741
		if (PageLRU(page)) {
L
Lee Schermerhorn 已提交
1742
			int lru = page_lru(page);
1743
			get_page(page);
1744
			ClearPageLRU(page);
1745 1746
			del_page_from_lru_list(page, lruvec, lru);
			ret = 0;
1747
		}
1748
		spin_unlock_irq(zone_lru_lock(zone));
1749 1750 1751 1752
	}
	return ret;
}

1753
/*
F
Fengguang Wu 已提交
1754 1755 1756 1757 1758
 * 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.
1759
 */
M
Mel Gorman 已提交
1760
static int too_many_isolated(struct pglist_data *pgdat, int file,
1761 1762 1763 1764 1765 1766 1767
		struct scan_control *sc)
{
	unsigned long inactive, isolated;

	if (current_is_kswapd())
		return 0;

1768
	if (!sane_reclaim(sc))
1769 1770 1771
		return 0;

	if (file) {
M
Mel Gorman 已提交
1772 1773
		inactive = node_page_state(pgdat, NR_INACTIVE_FILE);
		isolated = node_page_state(pgdat, NR_ISOLATED_FILE);
1774
	} else {
M
Mel Gorman 已提交
1775 1776
		inactive = node_page_state(pgdat, NR_INACTIVE_ANON);
		isolated = node_page_state(pgdat, NR_ISOLATED_ANON);
1777 1778
	}

1779 1780 1781 1782 1783
	/*
	 * 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.
	 */
1784
	if ((sc->gfp_mask & (__GFP_IO | __GFP_FS)) == (__GFP_IO | __GFP_FS))
1785 1786
		inactive >>= 3;

1787 1788 1789
	return isolated > inactive;
}

1790
static noinline_for_stack void
H
Hugh Dickins 已提交
1791
putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
1792
{
1793
	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
M
Mel Gorman 已提交
1794
	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1795
	LIST_HEAD(pages_to_free);
1796 1797 1798 1799 1800

	/*
	 * Put back any unfreeable pages.
	 */
	while (!list_empty(page_list)) {
1801
		struct page *page = lru_to_page(page_list);
1802
		int lru;
1803

1804
		VM_BUG_ON_PAGE(PageLRU(page), page);
1805
		list_del(&page->lru);
1806
		if (unlikely(!page_evictable(page))) {
M
Mel Gorman 已提交
1807
			spin_unlock_irq(&pgdat->lru_lock);
1808
			putback_lru_page(page);
M
Mel Gorman 已提交
1809
			spin_lock_irq(&pgdat->lru_lock);
1810 1811
			continue;
		}
1812

M
Mel Gorman 已提交
1813
		lruvec = mem_cgroup_page_lruvec(page, pgdat);
1814

1815
		SetPageLRU(page);
1816
		lru = page_lru(page);
1817 1818
		add_page_to_lru_list(page, lruvec, lru);

1819 1820
		if (is_active_lru(lru)) {
			int file = is_file_lru(lru);
1821 1822
			int numpages = hpage_nr_pages(page);
			reclaim_stat->recent_rotated[file] += numpages;
1823
		}
1824 1825 1826
		if (put_page_testzero(page)) {
			__ClearPageLRU(page);
			__ClearPageActive(page);
1827
			del_page_from_lru_list(page, lruvec, lru);
1828 1829

			if (unlikely(PageCompound(page))) {
M
Mel Gorman 已提交
1830
				spin_unlock_irq(&pgdat->lru_lock);
1831
				mem_cgroup_uncharge(page);
1832
				(*get_compound_page_dtor(page))(page);
M
Mel Gorman 已提交
1833
				spin_lock_irq(&pgdat->lru_lock);
1834 1835
			} else
				list_add(&page->lru, &pages_to_free);
1836 1837 1838
		}
	}

1839 1840 1841 1842
	/*
	 * To save our caller's stack, now use input list for pages to free.
	 */
	list_splice(&pages_to_free, page_list);
1843 1844
}

1845 1846 1847 1848 1849 1850 1851 1852 1853 1854 1855 1856 1857
/*
 * 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
1858
/*
1859
 * shrink_inactive_list() is a helper for shrink_node().  It returns the number
A
Andrew Morton 已提交
1860
 * of reclaimed pages
L
Linus Torvalds 已提交
1861
 */
1862
static noinline_for_stack unsigned long
1863
shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1864
		     struct scan_control *sc, enum lru_list lru)
L
Linus Torvalds 已提交
1865 1866
{
	LIST_HEAD(page_list);
1867
	unsigned long nr_scanned;
1868
	unsigned long nr_reclaimed = 0;
1869
	unsigned long nr_taken;
1870
	struct reclaim_stat stat = {};
1871
	isolate_mode_t isolate_mode = 0;
1872
	int file = is_file_lru(lru);
M
Mel Gorman 已提交
1873
	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1874
	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1875
	bool stalled = false;
1876

M
Mel Gorman 已提交
1877
	while (unlikely(too_many_isolated(pgdat, file, sc))) {
1878 1879 1880 1881 1882 1883
		if (stalled)
			return 0;

		/* wait a bit for the reclaimer. */
		msleep(100);
		stalled = true;
1884 1885 1886 1887 1888 1889

		/* 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
1890
	lru_add_drain();
1891 1892

	if (!sc->may_unmap)
1893
		isolate_mode |= ISOLATE_UNMAPPED;
1894

M
Mel Gorman 已提交
1895
	spin_lock_irq(&pgdat->lru_lock);
1896

1897 1898
	nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
				     &nr_scanned, sc, isolate_mode, lru);
1899

M
Mel Gorman 已提交
1900
	__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
1901
	reclaim_stat->recent_scanned[file] += nr_taken;
1902

1903 1904
	if (current_is_kswapd()) {
		if (global_reclaim(sc))
M
Mel Gorman 已提交
1905
			__count_vm_events(PGSCAN_KSWAPD, nr_scanned);
1906 1907 1908 1909
		count_memcg_events(lruvec_memcg(lruvec), PGSCAN_KSWAPD,
				   nr_scanned);
	} else {
		if (global_reclaim(sc))
M
Mel Gorman 已提交
1910
			__count_vm_events(PGSCAN_DIRECT, nr_scanned);
1911 1912
		count_memcg_events(lruvec_memcg(lruvec), PGSCAN_DIRECT,
				   nr_scanned);
1913
	}
M
Mel Gorman 已提交
1914
	spin_unlock_irq(&pgdat->lru_lock);
1915

1916
	if (nr_taken == 0)
1917
		return 0;
A
Andy Whitcroft 已提交
1918

S
Shaohua Li 已提交
1919
	nr_reclaimed = shrink_page_list(&page_list, pgdat, sc, 0,
1920
				&stat, false);
1921

M
Mel Gorman 已提交
1922
	spin_lock_irq(&pgdat->lru_lock);
1923

1924 1925
	if (current_is_kswapd()) {
		if (global_reclaim(sc))
M
Mel Gorman 已提交
1926
			__count_vm_events(PGSTEAL_KSWAPD, nr_reclaimed);
1927 1928 1929 1930
		count_memcg_events(lruvec_memcg(lruvec), PGSTEAL_KSWAPD,
				   nr_reclaimed);
	} else {
		if (global_reclaim(sc))
M
Mel Gorman 已提交
1931
			__count_vm_events(PGSTEAL_DIRECT, nr_reclaimed);
1932 1933
		count_memcg_events(lruvec_memcg(lruvec), PGSTEAL_DIRECT,
				   nr_reclaimed);
Y
Ying Han 已提交
1934
	}
N
Nick Piggin 已提交
1935

1936
	putback_inactive_pages(lruvec, &page_list);
1937

M
Mel Gorman 已提交
1938
	__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
1939

M
Mel Gorman 已提交
1940
	spin_unlock_irq(&pgdat->lru_lock);
1941

1942
	mem_cgroup_uncharge_list(&page_list);
1943
	free_unref_page_list(&page_list);
1944

1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958
	/*
	 * If dirty pages are scanned that are not queued for IO, it
	 * 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.
	 */
	if (stat.nr_unqueued_dirty == nr_taken)
		wakeup_flusher_threads(WB_REASON_VMSCAN);

1959 1960 1961 1962 1963 1964 1965 1966
	sc->nr.dirty += stat.nr_dirty;
	sc->nr.congested += stat.nr_congested;
	sc->nr.unqueued_dirty += stat.nr_unqueued_dirty;
	sc->nr.writeback += stat.nr_writeback;
	sc->nr.immediate += stat.nr_immediate;
	sc->nr.taken += nr_taken;
	if (file)
		sc->nr.file_taken += nr_taken;
1967

M
Mel Gorman 已提交
1968
	trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,
1969
			nr_scanned, nr_reclaimed, &stat, sc->priority, file);
1970
	return nr_reclaimed;
L
Linus Torvalds 已提交
1971 1972 1973 1974 1975 1976 1977 1978 1979
}

/*
 * 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
1980
 * appropriate to hold zone_lru_lock across the whole operation.  But if
L
Linus Torvalds 已提交
1981
 * the pages are mapped, the processing is slow (page_referenced()) so we
1982
 * should drop zone_lru_lock around each page.  It's impossible to balance
L
Linus Torvalds 已提交
1983 1984 1985 1986
 * 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.
 *
1987
 * The downside is that we have to touch page->_refcount against each page.
L
Linus Torvalds 已提交
1988
 * But we had to alter page->flags anyway.
1989 1990
 *
 * Returns the number of pages moved to the given lru.
L
Linus Torvalds 已提交
1991
 */
1992

1993
static unsigned move_active_pages_to_lru(struct lruvec *lruvec,
1994
				     struct list_head *list,
1995
				     struct list_head *pages_to_free,
1996 1997
				     enum lru_list lru)
{
M
Mel Gorman 已提交
1998
	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1999
	struct page *page;
2000
	int nr_pages;
2001
	int nr_moved = 0;
2002 2003 2004

	while (!list_empty(list)) {
		page = lru_to_page(list);
M
Mel Gorman 已提交
2005
		lruvec = mem_cgroup_page_lruvec(page, pgdat);
2006

2007
		VM_BUG_ON_PAGE(PageLRU(page), page);
2008 2009
		SetPageLRU(page);

2010
		nr_pages = hpage_nr_pages(page);
M
Mel Gorman 已提交
2011
		update_lru_size(lruvec, lru, page_zonenum(page), nr_pages);
2012
		list_move(&page->lru, &lruvec->lists[lru]);
2013

2014 2015 2016
		if (put_page_testzero(page)) {
			__ClearPageLRU(page);
			__ClearPageActive(page);
2017
			del_page_from_lru_list(page, lruvec, lru);
2018 2019

			if (unlikely(PageCompound(page))) {
M
Mel Gorman 已提交
2020
				spin_unlock_irq(&pgdat->lru_lock);
2021
				mem_cgroup_uncharge(page);
2022
				(*get_compound_page_dtor(page))(page);
M
Mel Gorman 已提交
2023
				spin_lock_irq(&pgdat->lru_lock);
2024 2025
			} else
				list_add(&page->lru, pages_to_free);
2026 2027
		} else {
			nr_moved += nr_pages;
2028 2029
		}
	}
2030

2031
	if (!is_active_lru(lru)) {
2032
		__count_vm_events(PGDEACTIVATE, nr_moved);
2033 2034 2035
		count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE,
				   nr_moved);
	}
2036 2037

	return nr_moved;
2038
}
2039

H
Hugh Dickins 已提交
2040
static void shrink_active_list(unsigned long nr_to_scan,
2041
			       struct lruvec *lruvec,
2042
			       struct scan_control *sc,
2043
			       enum lru_list lru)
L
Linus Torvalds 已提交
2044
{
2045
	unsigned long nr_taken;
H
Hugh Dickins 已提交
2046
	unsigned long nr_scanned;
2047
	unsigned long vm_flags;
L
Linus Torvalds 已提交
2048
	LIST_HEAD(l_hold);	/* The pages which were snipped off */
2049
	LIST_HEAD(l_active);
2050
	LIST_HEAD(l_inactive);
L
Linus Torvalds 已提交
2051
	struct page *page;
2052
	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
2053 2054
	unsigned nr_deactivate, nr_activate;
	unsigned nr_rotated = 0;
2055
	isolate_mode_t isolate_mode = 0;
2056
	int file = is_file_lru(lru);
M
Mel Gorman 已提交
2057
	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
L
Linus Torvalds 已提交
2058 2059

	lru_add_drain();
2060 2061

	if (!sc->may_unmap)
2062
		isolate_mode |= ISOLATE_UNMAPPED;
2063

M
Mel Gorman 已提交
2064
	spin_lock_irq(&pgdat->lru_lock);
2065

2066 2067
	nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
				     &nr_scanned, sc, isolate_mode, lru);
2068

M
Mel Gorman 已提交
2069
	__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
2070
	reclaim_stat->recent_scanned[file] += nr_taken;
2071

M
Mel Gorman 已提交
2072
	__count_vm_events(PGREFILL, nr_scanned);
2073
	count_memcg_events(lruvec_memcg(lruvec), PGREFILL, nr_scanned);
2074

M
Mel Gorman 已提交
2075
	spin_unlock_irq(&pgdat->lru_lock);
L
Linus Torvalds 已提交
2076 2077 2078 2079 2080

	while (!list_empty(&l_hold)) {
		cond_resched();
		page = lru_to_page(&l_hold);
		list_del(&page->lru);
2081

2082
		if (unlikely(!page_evictable(page))) {
L
Lee Schermerhorn 已提交
2083 2084 2085 2086
			putback_lru_page(page);
			continue;
		}

2087 2088 2089 2090 2091 2092 2093 2094
		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);
			}
		}

2095 2096
		if (page_referenced(page, 0, sc->target_mem_cgroup,
				    &vm_flags)) {
2097
			nr_rotated += hpage_nr_pages(page);
2098 2099 2100 2101 2102 2103 2104 2105 2106
			/*
			 * 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.
			 */
2107
			if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
2108 2109 2110 2111
				list_add(&page->lru, &l_active);
				continue;
			}
		}
2112

2113
		ClearPageActive(page);	/* we are de-activating */
L
Linus Torvalds 已提交
2114 2115 2116
		list_add(&page->lru, &l_inactive);
	}

2117
	/*
2118
	 * Move pages back to the lru list.
2119
	 */
M
Mel Gorman 已提交
2120
	spin_lock_irq(&pgdat->lru_lock);
2121
	/*
2122 2123 2124
	 * 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
2125
	 * get_scan_count.
2126
	 */
2127
	reclaim_stat->recent_rotated[file] += nr_rotated;
2128

2129 2130
	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
2131 2132
	__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
	spin_unlock_irq(&pgdat->lru_lock);
2133

2134
	mem_cgroup_uncharge_list(&l_hold);
2135
	free_unref_page_list(&l_hold);
2136 2137
	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
2138 2139
}

2140 2141 2142
/*
 * The inactive anon list should be small enough that the VM never has
 * to do too much work.
2143
 *
2144 2145 2146
 * 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.
2147
 *
2148 2149
 * Both inactive lists should also be large enough that each inactive
 * page has a chance to be referenced again before it is reclaimed.
2150
 *
2151 2152
 * If that fails and refaulting is observed, the inactive list grows.
 *
2153
 * The inactive_ratio is the target ratio of ACTIVE to INACTIVE pages
2154
 * on this LRU, maintained by the pageout code. An inactive_ratio
2155
 * of 3 means 3:1 or 25% of the pages are kept on the inactive list.
2156
 *
2157 2158 2159 2160 2161 2162 2163 2164 2165 2166
 * 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
2167
 */
2168
static bool inactive_list_is_low(struct lruvec *lruvec, bool file,
2169 2170
				 struct mem_cgroup *memcg,
				 struct scan_control *sc, bool actual_reclaim)
2171
{
2172
	enum lru_list active_lru = file * LRU_FILE + LRU_ACTIVE;
2173 2174 2175 2176 2177
	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;
2178
	unsigned long gb;
2179

2180 2181 2182 2183 2184 2185
	/*
	 * If we don't have swap space, anonymous page deactivation
	 * is pointless.
	 */
	if (!file && !total_swap_pages)
		return false;
2186

2187 2188
	inactive = lruvec_lru_size(lruvec, inactive_lru, sc->reclaim_idx);
	active = lruvec_lru_size(lruvec, active_lru, sc->reclaim_idx);
2189

2190
	if (memcg)
2191
		refaults = memcg_page_state(memcg, WORKINGSET_ACTIVATE);
2192
	else
2193 2194 2195 2196 2197 2198 2199 2200 2201 2202 2203 2204 2205 2206 2207 2208
		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;
	}
2209

2210 2211 2212 2213 2214
	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);
2215

2216
	return inactive * inactive_ratio < active;
2217 2218
}

2219
static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
2220 2221
				 struct lruvec *lruvec, struct mem_cgroup *memcg,
				 struct scan_control *sc)
2222
{
2223
	if (is_active_lru(lru)) {
2224 2225
		if (inactive_list_is_low(lruvec, is_file_lru(lru),
					 memcg, sc, true))
2226
			shrink_active_list(nr_to_scan, lruvec, sc, lru);
2227 2228 2229
		return 0;
	}

2230
	return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
2231 2232
}

2233 2234 2235 2236 2237 2238 2239
enum scan_balance {
	SCAN_EQUAL,
	SCAN_FRACT,
	SCAN_ANON,
	SCAN_FILE,
};

2240 2241 2242 2243 2244 2245
/*
 * 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
2246 2247
 * 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
2248
 */
2249
static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
2250 2251
			   struct scan_control *sc, unsigned long *nr,
			   unsigned long *lru_pages)
2252
{
2253
	int swappiness = mem_cgroup_swappiness(memcg);
2254 2255 2256
	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
	u64 fraction[2];
	u64 denominator = 0;	/* gcc */
M
Mel Gorman 已提交
2257
	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
2258
	unsigned long anon_prio, file_prio;
2259
	enum scan_balance scan_balance;
2260
	unsigned long anon, file;
2261
	unsigned long ap, fp;
H
Hugh Dickins 已提交
2262
	enum lru_list lru;
2263 2264

	/* If we have no swap space, do not bother scanning anon pages. */
2265
	if (!sc->may_swap || mem_cgroup_get_nr_swap_pages(memcg) <= 0) {
2266
		scan_balance = SCAN_FILE;
2267 2268
		goto out;
	}
2269

2270 2271 2272 2273 2274 2275 2276
	/*
	 * 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.
	 */
2277
	if (!global_reclaim(sc) && !swappiness) {
2278
		scan_balance = SCAN_FILE;
2279 2280 2281 2282 2283 2284 2285 2286
		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).
	 */
2287
	if (!sc->priority && swappiness) {
2288
		scan_balance = SCAN_EQUAL;
2289 2290 2291
		goto out;
	}

2292 2293 2294 2295 2296 2297 2298 2299 2300 2301
	/*
	 * 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
2302 2303 2304 2305
		unsigned long pgdatfile;
		unsigned long pgdatfree;
		int z;
		unsigned long total_high_wmark = 0;
2306

M
Mel Gorman 已提交
2307 2308 2309 2310 2311 2312
		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];
2313
			if (!managed_zone(zone))
M
Mel Gorman 已提交
2314 2315 2316 2317
				continue;

			total_high_wmark += high_wmark_pages(zone);
		}
2318

M
Mel Gorman 已提交
2319
		if (unlikely(pgdatfile + pgdatfree <= total_high_wmark)) {
2320 2321 2322 2323 2324 2325 2326 2327 2328 2329 2330
			/*
			 * 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;
			}
2331 2332 2333
		}
	}

2334
	/*
2335 2336 2337 2338 2339 2340 2341
	 * 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.
2342
	 */
2343
	if (!inactive_list_is_low(lruvec, true, memcg, sc, false) &&
2344
	    lruvec_lru_size(lruvec, LRU_INACTIVE_FILE, sc->reclaim_idx) >> sc->priority) {
2345
		scan_balance = SCAN_FILE;
2346 2347 2348
		goto out;
	}

2349 2350
	scan_balance = SCAN_FRACT;

2351 2352 2353 2354
	/*
	 * With swappiness at 100, anonymous and file have the same priority.
	 * This scanning priority is essentially the inverse of IO cost.
	 */
2355
	anon_prio = swappiness;
H
Hugh Dickins 已提交
2356
	file_prio = 200 - anon_prio;
2357

2358 2359 2360 2361 2362 2363 2364 2365 2366 2367 2368
	/*
	 * 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]
	 */
2369

2370 2371 2372 2373
	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);
2374

M
Mel Gorman 已提交
2375
	spin_lock_irq(&pgdat->lru_lock);
2376 2377 2378
	if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
		reclaim_stat->recent_scanned[0] /= 2;
		reclaim_stat->recent_rotated[0] /= 2;
2379 2380
	}

2381 2382 2383
	if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
		reclaim_stat->recent_scanned[1] /= 2;
		reclaim_stat->recent_rotated[1] /= 2;
2384 2385 2386
	}

	/*
2387 2388 2389
	 * 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.
2390
	 */
2391
	ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
2392
	ap /= reclaim_stat->recent_rotated[0] + 1;
2393

2394
	fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
2395
	fp /= reclaim_stat->recent_rotated[1] + 1;
M
Mel Gorman 已提交
2396
	spin_unlock_irq(&pgdat->lru_lock);
2397

2398 2399 2400 2401
	fraction[0] = ap;
	fraction[1] = fp;
	denominator = ap + fp + 1;
out:
2402 2403 2404 2405 2406
	*lru_pages = 0;
	for_each_evictable_lru(lru) {
		int file = is_file_lru(lru);
		unsigned long size;
		unsigned long scan;
2407

2408 2409 2410 2411 2412 2413 2414 2415
		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);
2416

2417 2418 2419 2420 2421
		switch (scan_balance) {
		case SCAN_EQUAL:
			/* Scan lists relative to size */
			break;
		case SCAN_FRACT:
2422
			/*
2423 2424
			 * Scan types proportional to swappiness and
			 * their relative recent reclaim efficiency.
2425
			 */
2426 2427 2428 2429 2430 2431 2432 2433 2434 2435 2436 2437 2438 2439
			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();
2440
		}
2441 2442 2443

		*lru_pages += size;
		nr[lru] = scan;
2444
	}
2445
}
2446

2447
/*
2448
 * This is a basic per-node page freer.  Used by both kswapd and direct reclaim.
2449
 */
2450
static void shrink_node_memcg(struct pglist_data *pgdat, struct mem_cgroup *memcg,
2451
			      struct scan_control *sc, unsigned long *lru_pages)
2452
{
2453
	struct lruvec *lruvec = mem_cgroup_lruvec(pgdat, memcg);
2454
	unsigned long nr[NR_LRU_LISTS];
2455
	unsigned long targets[NR_LRU_LISTS];
2456 2457 2458 2459 2460
	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;
2461
	bool scan_adjusted;
2462

2463
	get_scan_count(lruvec, memcg, sc, nr, lru_pages);
2464

2465 2466 2467
	/* Record the original scan target for proportional adjustments later */
	memcpy(targets, nr, sizeof(nr));

2468 2469 2470 2471 2472 2473 2474 2475 2476 2477 2478 2479 2480 2481
	/*
	 * 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);

2482 2483 2484
	blk_start_plug(&plug);
	while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
					nr[LRU_INACTIVE_FILE]) {
2485 2486 2487
		unsigned long nr_anon, nr_file, percentage;
		unsigned long nr_scanned;

2488 2489 2490 2491 2492 2493
		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,
2494
							    lruvec, memcg, sc);
2495 2496
			}
		}
2497

2498 2499
		cond_resched();

2500 2501 2502 2503 2504
		if (nr_reclaimed < nr_to_reclaim || scan_adjusted)
			continue;

		/*
		 * For kswapd and memcg, reclaim at least the number of pages
2505
		 * requested. Ensure that the anon and file LRUs are scanned
2506 2507 2508 2509 2510 2511 2512
		 * 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];

2513 2514 2515 2516 2517 2518 2519 2520 2521
		/*
		 * 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;

2522 2523 2524 2525 2526 2527 2528 2529 2530 2531 2532 2533 2534 2535 2536 2537 2538 2539 2540 2541 2542 2543 2544 2545 2546 2547 2548 2549 2550 2551 2552
		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;
2553 2554 2555 2556 2557 2558 2559 2560
	}
	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.
	 */
2561
	if (inactive_list_is_low(lruvec, false, memcg, sc, true))
2562 2563 2564 2565
		shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
				   sc, LRU_ACTIVE_ANON);
}

M
Mel Gorman 已提交
2566
/* Use reclaim/compaction for costly allocs or under memory pressure */
2567
static bool in_reclaim_compaction(struct scan_control *sc)
M
Mel Gorman 已提交
2568
{
2569
	if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
M
Mel Gorman 已提交
2570
			(sc->order > PAGE_ALLOC_COSTLY_ORDER ||
2571
			 sc->priority < DEF_PRIORITY - 2))
M
Mel Gorman 已提交
2572 2573 2574 2575 2576
		return true;

	return false;
}

2577
/*
M
Mel Gorman 已提交
2578 2579 2580 2581 2582
 * 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.
2583
 */
2584
static inline bool should_continue_reclaim(struct pglist_data *pgdat,
2585 2586 2587 2588 2589 2590
					unsigned long nr_reclaimed,
					unsigned long nr_scanned,
					struct scan_control *sc)
{
	unsigned long pages_for_compaction;
	unsigned long inactive_lru_pages;
2591
	int z;
2592 2593

	/* If not in reclaim/compaction mode, stop */
2594
	if (!in_reclaim_compaction(sc))
2595 2596
		return false;

2597
	/* Consider stopping depending on scan and reclaim activity */
2598
	if (sc->gfp_mask & __GFP_RETRY_MAYFAIL) {
2599
		/*
2600
		 * For __GFP_RETRY_MAYFAIL allocations, stop reclaiming if the
2601 2602
		 * full LRU list has been scanned and we are still failing
		 * to reclaim pages. This full LRU scan is potentially
2603
		 * expensive but a __GFP_RETRY_MAYFAIL caller really wants to succeed
2604 2605 2606 2607 2608
		 */
		if (!nr_reclaimed && !nr_scanned)
			return false;
	} else {
		/*
2609
		 * For non-__GFP_RETRY_MAYFAIL allocations which can presumably
2610 2611 2612 2613 2614 2615 2616 2617 2618
		 * 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;
	}
2619 2620 2621 2622 2623

	/*
	 * If we have not reclaimed enough pages for compaction and the
	 * inactive lists are large enough, continue reclaiming
	 */
2624
	pages_for_compaction = compact_gap(sc->order);
2625
	inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE);
2626
	if (get_nr_swap_pages() > 0)
2627
		inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);
2628 2629 2630 2631 2632
	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 */
2633 2634
	for (z = 0; z <= sc->reclaim_idx; z++) {
		struct zone *zone = &pgdat->node_zones[z];
2635
		if (!managed_zone(zone))
2636 2637 2638
			continue;

		switch (compaction_suitable(zone, sc->order, 0, sc->reclaim_idx)) {
2639
		case COMPACT_SUCCESS:
2640 2641 2642 2643 2644 2645
		case COMPACT_CONTINUE:
			return false;
		default:
			/* check next zone */
			;
		}
2646
	}
2647
	return true;
2648 2649
}

2650 2651 2652 2653 2654 2655
static bool pgdat_memcg_congested(pg_data_t *pgdat, struct mem_cgroup *memcg)
{
	return test_bit(PGDAT_CONGESTED, &pgdat->flags) ||
		(memcg && memcg_congested(pgdat, memcg));
}

2656
static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
L
Linus Torvalds 已提交
2657
{
2658
	struct reclaim_state *reclaim_state = current->reclaim_state;
2659
	unsigned long nr_reclaimed, nr_scanned;
2660
	bool reclaimable = false;
L
Linus Torvalds 已提交
2661

2662 2663 2664
	do {
		struct mem_cgroup *root = sc->target_mem_cgroup;
		struct mem_cgroup_reclaim_cookie reclaim = {
2665
			.pgdat = pgdat,
2666 2667
			.priority = sc->priority,
		};
2668
		unsigned long node_lru_pages = 0;
2669
		struct mem_cgroup *memcg;
2670

2671 2672
		memset(&sc->nr, 0, sizeof(sc->nr));

2673 2674
		nr_reclaimed = sc->nr_reclaimed;
		nr_scanned = sc->nr_scanned;
L
Linus Torvalds 已提交
2675

2676 2677
		memcg = mem_cgroup_iter(root, NULL, &reclaim);
		do {
2678
			unsigned long lru_pages;
2679
			unsigned long reclaimed;
2680
			unsigned long scanned;
2681

R
Roman Gushchin 已提交
2682 2683 2684 2685 2686 2687 2688 2689 2690 2691 2692 2693 2694 2695
			switch (mem_cgroup_protected(root, memcg)) {
			case MEMCG_PROT_MIN:
				/*
				 * Hard protection.
				 * If there is no reclaimable memory, OOM.
				 */
				continue;
			case MEMCG_PROT_LOW:
				/*
				 * Soft protection.
				 * Respect the protection only as long as
				 * there is an unprotected supply
				 * of reclaimable memory from other cgroups.
				 */
2696 2697
				if (!sc->memcg_low_reclaim) {
					sc->memcg_low_skipped = 1;
2698
					continue;
2699
				}
2700
				memcg_memory_event(memcg, MEMCG_LOW);
R
Roman Gushchin 已提交
2701 2702 2703
				break;
			case MEMCG_PROT_NONE:
				break;
2704 2705
			}

2706
			reclaimed = sc->nr_reclaimed;
2707
			scanned = sc->nr_scanned;
2708 2709
			shrink_node_memcg(pgdat, memcg, sc, &lru_pages);
			node_lru_pages += lru_pages;
2710

2711
			if (memcg)
2712
				shrink_slab(sc->gfp_mask, pgdat->node_id,
2713
					    memcg, sc->priority);
2714

2715 2716 2717 2718 2719
			/* Record the group's reclaim efficiency */
			vmpressure(sc->gfp_mask, memcg, false,
				   sc->nr_scanned - scanned,
				   sc->nr_reclaimed - reclaimed);

2720
			/*
2721 2722
			 * Direct reclaim and kswapd have to scan all memory
			 * cgroups to fulfill the overall scan target for the
2723
			 * node.
2724 2725 2726 2727 2728
			 *
			 * 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.
2729
			 */
2730 2731
			if (!global_reclaim(sc) &&
					sc->nr_reclaimed >= sc->nr_to_reclaim) {
2732 2733 2734
				mem_cgroup_iter_break(root, memcg);
				break;
			}
2735
		} while ((memcg = mem_cgroup_iter(root, memcg, &reclaim)));
2736

2737
		if (global_reclaim(sc))
2738
			shrink_slab(sc->gfp_mask, pgdat->node_id, NULL,
2739
				    sc->priority);
2740 2741 2742 2743

		if (reclaim_state) {
			sc->nr_reclaimed += reclaim_state->reclaimed_slab;
			reclaim_state->reclaimed_slab = 0;
2744 2745
		}

2746 2747
		/* Record the subtree's reclaim efficiency */
		vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true,
2748 2749 2750
			   sc->nr_scanned - nr_scanned,
			   sc->nr_reclaimed - nr_reclaimed);

2751 2752 2753
		if (sc->nr_reclaimed - nr_reclaimed)
			reclaimable = true;

2754 2755 2756 2757 2758 2759 2760 2761 2762 2763 2764 2765 2766 2767 2768 2769 2770 2771 2772 2773
		if (current_is_kswapd()) {
			/*
			 * If reclaim is isolating dirty pages under writeback,
			 * it implies that the long-lived page allocation rate
			 * is exceeding the page laundering rate. Either the
			 * global limits are not being effective at throttling
			 * processes due to the page distribution throughout
			 * zones or there is heavy usage of a slow backing
			 * device. The only option is to throttle from reclaim
			 * context which is not ideal as there is no guarantee
			 * the dirtying process is throttled in the same way
			 * balance_dirty_pages() manages.
			 *
			 * Once a node is flagged PGDAT_WRITEBACK, kswapd will
			 * count the number of pages under pages flagged for
			 * immediate reclaim and stall if any are encountered
			 * in the nr_immediate check below.
			 */
			if (sc->nr.writeback && sc->nr.writeback == sc->nr.taken)
				set_bit(PGDAT_WRITEBACK, &pgdat->flags);
2774 2775 2776 2777 2778 2779 2780 2781 2782 2783 2784 2785 2786 2787 2788 2789 2790 2791 2792 2793 2794 2795 2796

			/*
			 * Tag a node as congested if all the dirty pages
			 * scanned were backed by a congested BDI and
			 * wait_iff_congested will stall.
			 */
			if (sc->nr.dirty && sc->nr.dirty == sc->nr.congested)
				set_bit(PGDAT_CONGESTED, &pgdat->flags);

			/* Allow kswapd to start writing pages during reclaim.*/
			if (sc->nr.unqueued_dirty == sc->nr.file_taken)
				set_bit(PGDAT_DIRTY, &pgdat->flags);

			/*
			 * If kswapd scans pages marked marked for immediate
			 * reclaim and under writeback (nr_immediate), it
			 * implies that pages are cycling through the LRU
			 * faster than they are written so also forcibly stall.
			 */
			if (sc->nr.immediate)
				congestion_wait(BLK_RW_ASYNC, HZ/10);
		}

2797 2798 2799 2800 2801 2802 2803 2804
		/*
		 * Legacy memcg will stall in page writeback so avoid forcibly
		 * stalling in wait_iff_congested().
		 */
		if (!global_reclaim(sc) && sane_reclaim(sc) &&
		    sc->nr.dirty && sc->nr.dirty == sc->nr.congested)
			set_memcg_congestion(pgdat, root, true);

2805 2806 2807 2808 2809 2810 2811
		/*
		 * Stall direct reclaim for IO completions if underlying BDIs
		 * and node is congested. Allow kswapd to continue until it
		 * starts encountering unqueued dirty pages or cycling through
		 * the LRU too quickly.
		 */
		if (!sc->hibernation_mode && !current_is_kswapd() &&
2812 2813
		   current_may_throttle() && pgdat_memcg_congested(pgdat, root))
			wait_iff_congested(BLK_RW_ASYNC, HZ/10);
2814

2815
	} while (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed,
2816
					 sc->nr_scanned - nr_scanned, sc));
2817

2818 2819 2820 2821 2822 2823 2824 2825 2826
	/*
	 * 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;

2827
	return reclaimable;
2828 2829
}

2830
/*
2831 2832 2833
 * 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.
2834
 */
2835
static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
2836
{
M
Mel Gorman 已提交
2837
	unsigned long watermark;
2838
	enum compact_result suitable;
2839

2840 2841 2842 2843 2844 2845 2846
	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;
2847

2848
	/*
2849 2850 2851 2852 2853 2854 2855
	 * 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.
2856
	 */
2857
	watermark = high_wmark_pages(zone) + compact_gap(sc->order);
2858

2859
	return zone_watermark_ok_safe(zone, 0, watermark, sc->reclaim_idx);
2860 2861
}

L
Linus Torvalds 已提交
2862 2863 2864 2865 2866 2867 2868 2869
/*
 * 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
2870
static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
L
Linus Torvalds 已提交
2871
{
2872
	struct zoneref *z;
2873
	struct zone *zone;
2874 2875
	unsigned long nr_soft_reclaimed;
	unsigned long nr_soft_scanned;
2876
	gfp_t orig_mask;
2877
	pg_data_t *last_pgdat = NULL;
2878

2879 2880 2881 2882 2883
	/*
	 * 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
	 */
2884
	orig_mask = sc->gfp_mask;
2885
	if (buffer_heads_over_limit) {
2886
		sc->gfp_mask |= __GFP_HIGHMEM;
2887
		sc->reclaim_idx = gfp_zone(sc->gfp_mask);
2888
	}
2889

2890
	for_each_zone_zonelist_nodemask(zone, z, zonelist,
2891
					sc->reclaim_idx, sc->nodemask) {
2892 2893 2894 2895
		/*
		 * Take care memory controller reclaiming has small influence
		 * to global LRU.
		 */
2896
		if (global_reclaim(sc)) {
2897 2898
			if (!cpuset_zone_allowed(zone,
						 GFP_KERNEL | __GFP_HARDWALL))
2899
				continue;
2900

2901 2902 2903 2904 2905 2906 2907 2908 2909 2910 2911
			/*
			 * 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 &&
2912
			    compaction_ready(zone, sc)) {
2913 2914
				sc->compaction_ready = true;
				continue;
2915
			}
2916

2917 2918 2919 2920 2921 2922 2923 2924 2925
			/*
			 * 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;

2926 2927 2928 2929 2930 2931 2932
			/*
			 * 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;
2933
			nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone->zone_pgdat,
2934 2935 2936 2937
						sc->order, sc->gfp_mask,
						&nr_soft_scanned);
			sc->nr_reclaimed += nr_soft_reclaimed;
			sc->nr_scanned += nr_soft_scanned;
2938
			/* need some check for avoid more shrink_zone() */
2939
		}
2940

2941 2942 2943 2944
		/* See comment about same check for global reclaim above */
		if (zone->zone_pgdat == last_pgdat)
			continue;
		last_pgdat = zone->zone_pgdat;
2945
		shrink_node(zone->zone_pgdat, sc);
L
Linus Torvalds 已提交
2946
	}
2947

2948 2949 2950 2951 2952
	/*
	 * 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
2953
}
2954

2955 2956 2957 2958 2959 2960 2961 2962 2963 2964
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)
2965
			refaults = memcg_page_state(memcg, WORKINGSET_ACTIVATE);
2966 2967 2968 2969 2970 2971 2972 2973
		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
2974 2975 2976 2977 2978 2979 2980 2981
/*
 * 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
2982 2983 2984 2985
 * 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.
2986 2987 2988
 *
 * returns:	0, if no pages reclaimed
 * 		else, the number of pages reclaimed
L
Linus Torvalds 已提交
2989
 */
2990
static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2991
					  struct scan_control *sc)
L
Linus Torvalds 已提交
2992
{
2993
	int initial_priority = sc->priority;
2994 2995 2996
	pg_data_t *last_pgdat;
	struct zoneref *z;
	struct zone *zone;
2997
retry:
2998 2999
	delayacct_freepages_start();

3000
	if (global_reclaim(sc))
3001
		__count_zid_vm_events(ALLOCSTALL, sc->reclaim_idx, 1);
L
Linus Torvalds 已提交
3002

3003
	do {
3004 3005
		vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
				sc->priority);
3006
		sc->nr_scanned = 0;
M
Michal Hocko 已提交
3007
		shrink_zones(zonelist, sc);
3008

3009
		if (sc->nr_reclaimed >= sc->nr_to_reclaim)
3010 3011 3012 3013
			break;

		if (sc->compaction_ready)
			break;
L
Linus Torvalds 已提交
3014

3015 3016 3017 3018 3019 3020
		/*
		 * If we're getting trouble reclaiming, start doing
		 * writepage even in laptop mode.
		 */
		if (sc->priority < DEF_PRIORITY - 2)
			sc->may_writepage = 1;
3021
	} while (--sc->priority >= 0);
3022

3023 3024 3025 3026 3027 3028 3029
	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);
3030
		set_memcg_congestion(last_pgdat, sc->target_mem_cgroup, false);
3031 3032
	}

3033 3034
	delayacct_freepages_end();

3035 3036 3037
	if (sc->nr_reclaimed)
		return sc->nr_reclaimed;

3038
	/* Aborted reclaim to try compaction? don't OOM, then */
3039
	if (sc->compaction_ready)
3040 3041
		return 1;

3042
	/* Untapped cgroup reserves?  Don't OOM, retry. */
3043
	if (sc->memcg_low_skipped) {
3044
		sc->priority = initial_priority;
3045 3046
		sc->memcg_low_reclaim = 1;
		sc->memcg_low_skipped = 0;
3047 3048 3049
		goto retry;
	}

3050
	return 0;
L
Linus Torvalds 已提交
3051 3052
}

3053
static bool allow_direct_reclaim(pg_data_t *pgdat)
3054 3055 3056 3057 3058 3059 3060
{
	struct zone *zone;
	unsigned long pfmemalloc_reserve = 0;
	unsigned long free_pages = 0;
	int i;
	bool wmark_ok;

3061 3062 3063
	if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
		return true;

3064 3065
	for (i = 0; i <= ZONE_NORMAL; i++) {
		zone = &pgdat->node_zones[i];
3066 3067 3068 3069
		if (!managed_zone(zone))
			continue;

		if (!zone_reclaimable_pages(zone))
3070 3071
			continue;

3072 3073 3074 3075
		pfmemalloc_reserve += min_wmark_pages(zone);
		free_pages += zone_page_state(zone, NR_FREE_PAGES);
	}

3076 3077 3078 3079
	/* If there are no reserves (unexpected config) then do not throttle */
	if (!pfmemalloc_reserve)
		return true;

3080 3081 3082 3083
	wmark_ok = free_pages > pfmemalloc_reserve / 2;

	/* kswapd must be awake if processes are being throttled */
	if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
3084
		pgdat->kswapd_classzone_idx = min(pgdat->kswapd_classzone_idx,
3085 3086 3087 3088 3089 3090 3091 3092 3093 3094 3095
						(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
3096 3097 3098 3099
 * 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.
3100
 */
3101
static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
3102 3103
					nodemask_t *nodemask)
{
3104
	struct zoneref *z;
3105
	struct zone *zone;
3106
	pg_data_t *pgdat = NULL;
3107 3108 3109 3110 3111 3112 3113 3114 3115

	/*
	 * 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)
3116 3117 3118 3119 3120 3121 3122 3123
		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;
3124

3125 3126 3127 3128 3129 3130 3131 3132 3133 3134 3135 3136 3137 3138 3139
	/*
	 * 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,
3140
					gfp_zone(gfp_mask), nodemask) {
3141 3142 3143 3144 3145
		if (zone_idx(zone) > ZONE_NORMAL)
			continue;

		/* Throttle based on the first usable node */
		pgdat = zone->zone_pgdat;
3146
		if (allow_direct_reclaim(pgdat))
3147 3148 3149 3150 3151 3152
			goto out;
		break;
	}

	/* If no zone was usable by the allocation flags then do not throttle */
	if (!pgdat)
3153
		goto out;
3154

3155 3156 3157
	/* Account for the throttling */
	count_vm_event(PGSCAN_DIRECT_THROTTLE);

3158 3159 3160 3161 3162 3163 3164 3165 3166 3167
	/*
	 * 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,
3168
			allow_direct_reclaim(pgdat), HZ);
3169 3170

		goto check_pending;
3171 3172 3173 3174
	}

	/* Throttle until kswapd wakes the process */
	wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
3175
		allow_direct_reclaim(pgdat));
3176 3177 3178 3179 3180 3181 3182

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

out:
	return false;
3183 3184
}

3185
unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
3186
				gfp_t gfp_mask, nodemask_t *nodemask)
3187
{
3188
	unsigned long nr_reclaimed;
3189
	struct scan_control sc = {
3190
		.nr_to_reclaim = SWAP_CLUSTER_MAX,
3191
		.gfp_mask = current_gfp_context(gfp_mask),
3192
		.reclaim_idx = gfp_zone(gfp_mask),
3193 3194 3195
		.order = order,
		.nodemask = nodemask,
		.priority = DEF_PRIORITY,
3196
		.may_writepage = !laptop_mode,
3197
		.may_unmap = 1,
3198
		.may_swap = 1,
3199 3200
	};

G
Greg Thelen 已提交
3201 3202 3203 3204 3205 3206 3207 3208
	/*
	 * scan_control uses s8 fields for order, priority, and reclaim_idx.
	 * Confirm they are large enough for max values.
	 */
	BUILD_BUG_ON(MAX_ORDER > S8_MAX);
	BUILD_BUG_ON(DEF_PRIORITY > S8_MAX);
	BUILD_BUG_ON(MAX_NR_ZONES > S8_MAX);

3209
	/*
3210 3211 3212
	 * 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.
3213
	 */
3214
	if (throttle_direct_reclaim(sc.gfp_mask, zonelist, nodemask))
3215 3216
		return 1;

3217 3218
	trace_mm_vmscan_direct_reclaim_begin(order,
				sc.may_writepage,
3219
				sc.gfp_mask,
3220
				sc.reclaim_idx);
3221

3222
	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3223 3224 3225 3226

	trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);

	return nr_reclaimed;
3227 3228
}

A
Andrew Morton 已提交
3229
#ifdef CONFIG_MEMCG
3230

3231
unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg,
3232
						gfp_t gfp_mask, bool noswap,
3233
						pg_data_t *pgdat,
3234
						unsigned long *nr_scanned)
3235 3236
{
	struct scan_control sc = {
3237
		.nr_to_reclaim = SWAP_CLUSTER_MAX,
3238
		.target_mem_cgroup = memcg,
3239 3240
		.may_writepage = !laptop_mode,
		.may_unmap = 1,
3241
		.reclaim_idx = MAX_NR_ZONES - 1,
3242 3243
		.may_swap = !noswap,
	};
3244
	unsigned long lru_pages;
3245

3246 3247
	sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
			(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
3248

3249
	trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
3250
						      sc.may_writepage,
3251 3252
						      sc.gfp_mask,
						      sc.reclaim_idx);
3253

3254 3255 3256
	/*
	 * NOTE: Although we can get the priority field, using it
	 * here is not a good idea, since it limits the pages we can scan.
3257
	 * if we don't reclaim here, the shrink_node from balance_pgdat
3258 3259 3260
	 * will pick up pages from other mem cgroup's as well. We hack
	 * the priority and make it zero.
	 */
3261
	shrink_node_memcg(pgdat, memcg, &sc, &lru_pages);
3262 3263 3264

	trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);

3265
	*nr_scanned = sc.nr_scanned;
3266 3267 3268
	return sc.nr_reclaimed;
}

3269
unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
3270
					   unsigned long nr_pages,
K
KOSAKI Motohiro 已提交
3271
					   gfp_t gfp_mask,
3272
					   bool may_swap)
3273
{
3274
	struct zonelist *zonelist;
3275
	unsigned long nr_reclaimed;
3276
	int nid;
3277
	unsigned int noreclaim_flag;
3278
	struct scan_control sc = {
3279
		.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3280
		.gfp_mask = (current_gfp_context(gfp_mask) & GFP_RECLAIM_MASK) |
3281
				(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
3282
		.reclaim_idx = MAX_NR_ZONES - 1,
3283 3284 3285 3286
		.target_mem_cgroup = memcg,
		.priority = DEF_PRIORITY,
		.may_writepage = !laptop_mode,
		.may_unmap = 1,
3287
		.may_swap = may_swap,
3288
	};
3289

3290 3291 3292 3293 3294
	/*
	 * 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.
	 */
3295
	nid = mem_cgroup_select_victim_node(memcg);
3296

3297
	zonelist = &NODE_DATA(nid)->node_zonelists[ZONELIST_FALLBACK];
3298 3299 3300

	trace_mm_vmscan_memcg_reclaim_begin(0,
					    sc.may_writepage,
3301 3302
					    sc.gfp_mask,
					    sc.reclaim_idx);
3303

3304
	noreclaim_flag = memalloc_noreclaim_save();
3305
	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3306
	memalloc_noreclaim_restore(noreclaim_flag);
3307 3308 3309 3310

	trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);

	return nr_reclaimed;
3311 3312 3313
}
#endif

3314
static void age_active_anon(struct pglist_data *pgdat,
3315
				struct scan_control *sc)
3316
{
3317
	struct mem_cgroup *memcg;
3318

3319 3320 3321 3322 3323
	if (!total_swap_pages)
		return;

	memcg = mem_cgroup_iter(NULL, NULL, NULL);
	do {
3324
		struct lruvec *lruvec = mem_cgroup_lruvec(pgdat, memcg);
3325

3326
		if (inactive_list_is_low(lruvec, false, memcg, sc, true))
3327
			shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
3328
					   sc, LRU_ACTIVE_ANON);
3329 3330 3331

		memcg = mem_cgroup_iter(NULL, memcg, NULL);
	} while (memcg);
3332 3333
}

3334 3335 3336 3337 3338
/*
 * 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)
3339
{
3340 3341 3342
	int i;
	unsigned long mark = -1;
	struct zone *zone;
3343

3344 3345
	for (i = 0; i <= classzone_idx; i++) {
		zone = pgdat->node_zones + i;
3346

3347 3348 3349 3350 3351 3352 3353 3354 3355 3356 3357 3358 3359 3360 3361 3362 3363
		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;
3364 3365
}

3366 3367 3368 3369 3370 3371 3372 3373
/* 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);
}

3374 3375 3376 3377 3378 3379
/*
 * 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
 */
3380
static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, int classzone_idx)
3381
{
3382
	/*
3383
	 * The throttled processes are normally woken up in balance_pgdat() as
3384
	 * soon as allow_direct_reclaim() is true. But there is a potential
3385 3386 3387 3388 3389 3390 3391 3392 3393
	 * 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().
3394
	 */
3395 3396
	if (waitqueue_active(&pgdat->pfmemalloc_wait))
		wake_up_all(&pgdat->pfmemalloc_wait);
3397

3398 3399 3400 3401
	/* Hopeless node, leave it to direct reclaim */
	if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
		return true;

3402 3403 3404
	if (pgdat_balanced(pgdat, order, classzone_idx)) {
		clear_pgdat_congested(pgdat);
		return true;
3405 3406
	}

3407
	return false;
3408 3409
}

3410
/*
3411 3412
 * kswapd shrinks a node of pages that are at or below the highest usable
 * zone that is currently unbalanced.
3413 3414
 *
 * Returns true if kswapd scanned at least the requested number of pages to
3415 3416
 * 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.
3417
 */
3418
static bool kswapd_shrink_node(pg_data_t *pgdat,
3419
			       struct scan_control *sc)
3420
{
3421 3422
	struct zone *zone;
	int z;
3423

3424 3425
	/* Reclaim a number of pages proportional to the number of zones */
	sc->nr_to_reclaim = 0;
3426
	for (z = 0; z <= sc->reclaim_idx; z++) {
3427
		zone = pgdat->node_zones + z;
3428
		if (!managed_zone(zone))
3429
			continue;
3430

3431 3432
		sc->nr_to_reclaim += max(high_wmark_pages(zone), SWAP_CLUSTER_MAX);
	}
3433 3434

	/*
3435 3436
	 * Historically care was taken to put equal pressure on all zones but
	 * now pressure is applied based on node LRU order.
3437
	 */
3438
	shrink_node(pgdat, sc);
3439

3440
	/*
3441 3442 3443 3444 3445
	 * 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.
3446
	 */
3447
	if (sc->order && sc->nr_reclaimed >= compact_gap(sc->order))
3448
		sc->order = 0;
3449

3450
	return sc->nr_scanned >= sc->nr_to_reclaim;
3451 3452
}

L
Linus Torvalds 已提交
3453
/*
3454 3455 3456
 * 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
3457
 *
3458
 * Returns the order kswapd finished reclaiming at.
L
Linus Torvalds 已提交
3459 3460
 *
 * kswapd scans the zones in the highmem->normal->dma direction.  It skips
3461
 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
3462 3463 3464
 * 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
3465
 */
3466
static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
L
Linus Torvalds 已提交
3467 3468
{
	int i;
3469 3470
	unsigned long nr_soft_reclaimed;
	unsigned long nr_soft_scanned;
3471
	struct zone *zone;
3472 3473
	struct scan_control sc = {
		.gfp_mask = GFP_KERNEL,
3474
		.order = order,
3475
		.priority = DEF_PRIORITY,
3476
		.may_writepage = !laptop_mode,
3477
		.may_unmap = 1,
3478
		.may_swap = 1,
3479
	};
3480 3481 3482

	__fs_reclaim_acquire();

3483
	count_vm_event(PAGEOUTRUN);
L
Linus Torvalds 已提交
3484

3485
	do {
3486
		unsigned long nr_reclaimed = sc.nr_reclaimed;
3487
		bool raise_priority = true;
3488
		bool ret;
3489

3490
		sc.reclaim_idx = classzone_idx;
L
Linus Torvalds 已提交
3491

3492
		/*
3493 3494 3495 3496 3497 3498 3499 3500
		 * 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.
3501 3502 3503 3504
		 */
		if (buffer_heads_over_limit) {
			for (i = MAX_NR_ZONES - 1; i >= 0; i--) {
				zone = pgdat->node_zones + i;
3505
				if (!managed_zone(zone))
3506
					continue;
3507

3508
				sc.reclaim_idx = i;
A
Andrew Morton 已提交
3509
				break;
L
Linus Torvalds 已提交
3510 3511
			}
		}
3512

3513
		/*
3514 3515 3516
		 * 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.
3517
		 */
3518 3519
		if (pgdat_balanced(pgdat, sc.order, classzone_idx))
			goto out;
A
Andrew Morton 已提交
3520

3521 3522 3523 3524 3525 3526
		/*
		 * 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.
		 */
3527
		age_active_anon(pgdat, &sc);
3528

3529 3530 3531 3532
		/*
		 * If we're getting trouble reclaiming, start doing writepage
		 * even in laptop mode.
		 */
3533
		if (sc.priority < DEF_PRIORITY - 2)
3534 3535
			sc.may_writepage = 1;

3536 3537 3538
		/* Call soft limit reclaim before calling shrink_node. */
		sc.nr_scanned = 0;
		nr_soft_scanned = 0;
3539
		nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(pgdat, sc.order,
3540 3541 3542
						sc.gfp_mask, &nr_soft_scanned);
		sc.nr_reclaimed += nr_soft_reclaimed;

L
Linus Torvalds 已提交
3543
		/*
3544 3545 3546
		 * 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
3547
		 */
3548
		if (kswapd_shrink_node(pgdat, &sc))
3549
			raise_priority = false;
3550 3551 3552 3553 3554 3555 3556

		/*
		 * 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) &&
3557
				allow_direct_reclaim(pgdat))
3558
			wake_up_all(&pgdat->pfmemalloc_wait);
3559

3560
		/* Check if kswapd should be suspending */
3561 3562 3563 3564
		__fs_reclaim_release();
		ret = try_to_freeze();
		__fs_reclaim_acquire();
		if (ret || kthread_should_stop())
3565
			break;
3566

3567
		/*
3568 3569
		 * Raise priority if scanning rate is too low or there was no
		 * progress in reclaiming pages
3570
		 */
3571 3572
		nr_reclaimed = sc.nr_reclaimed - nr_reclaimed;
		if (raise_priority || !nr_reclaimed)
3573
			sc.priority--;
3574
	} while (sc.priority >= 1);
L
Linus Torvalds 已提交
3575

3576 3577 3578
	if (!sc.nr_reclaimed)
		pgdat->kswapd_failures++;

3579
out:
3580
	snapshot_refaults(NULL, pgdat);
3581
	__fs_reclaim_release();
3582
	/*
3583 3584 3585 3586
	 * 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.
3587
	 */
3588
	return sc.order;
L
Linus Torvalds 已提交
3589 3590
}

3591 3592 3593 3594 3595 3596 3597 3598 3599 3600 3601 3602 3603 3604 3605 3606
/*
 * 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);
}

3607 3608
static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_order,
				unsigned int classzone_idx)
3609 3610 3611 3612 3613 3614 3615 3616 3617
{
	long remaining = 0;
	DEFINE_WAIT(wait);

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

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

3618 3619 3620 3621 3622 3623 3624
	/*
	 * 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.
	 */
3625
	if (prepare_kswapd_sleep(pgdat, reclaim_order, classzone_idx)) {
3626 3627 3628 3629 3630 3631 3632 3633 3634 3635 3636 3637
		/*
		 * 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.
		 */
3638
		wakeup_kcompactd(pgdat, alloc_order, classzone_idx);
3639

3640
		remaining = schedule_timeout(HZ/10);
3641 3642 3643 3644 3645 3646 3647

		/*
		 * 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) {
3648
			pgdat->kswapd_classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx);
3649 3650 3651
			pgdat->kswapd_order = max(pgdat->kswapd_order, reclaim_order);
		}

3652 3653 3654 3655 3656 3657 3658 3659
		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.
	 */
3660 3661
	if (!remaining &&
	    prepare_kswapd_sleep(pgdat, reclaim_order, classzone_idx)) {
3662 3663 3664 3665 3666 3667 3668 3669 3670 3671 3672
		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);
3673 3674 3675 3676

		if (!kthread_should_stop())
			schedule();

3677 3678 3679 3680 3681 3682 3683 3684 3685 3686
		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
3687 3688
/*
 * The background pageout daemon, started as a kernel thread
3689
 * from the init process.
L
Linus Torvalds 已提交
3690 3691 3692 3693 3694 3695 3696 3697 3698 3699 3700 3701
 *
 * 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)
{
3702 3703
	unsigned int alloc_order, reclaim_order;
	unsigned int classzone_idx = MAX_NR_ZONES - 1;
L
Linus Torvalds 已提交
3704 3705
	pg_data_t *pgdat = (pg_data_t*)p;
	struct task_struct *tsk = current;
3706

L
Linus Torvalds 已提交
3707 3708 3709
	struct reclaim_state reclaim_state = {
		.reclaimed_slab = 0,
	};
3710
	const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
L
Linus Torvalds 已提交
3711

R
Rusty Russell 已提交
3712
	if (!cpumask_empty(cpumask))
3713
		set_cpus_allowed_ptr(tsk, cpumask);
L
Linus Torvalds 已提交
3714 3715 3716 3717 3718 3719 3720 3721 3722 3723 3724 3725 3726 3727
	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).
	 */
3728
	tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
3729
	set_freezable();
L
Linus Torvalds 已提交
3730

3731 3732
	pgdat->kswapd_order = 0;
	pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
L
Linus Torvalds 已提交
3733
	for ( ; ; ) {
3734
		bool ret;
3735

3736 3737 3738
		alloc_order = reclaim_order = pgdat->kswapd_order;
		classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx);

3739 3740 3741
kswapd_try_sleep:
		kswapd_try_to_sleep(pgdat, alloc_order, reclaim_order,
					classzone_idx);
3742

3743 3744
		/* Read the new order and classzone_idx */
		alloc_order = reclaim_order = pgdat->kswapd_order;
3745
		classzone_idx = kswapd_classzone_idx(pgdat, 0);
3746
		pgdat->kswapd_order = 0;
3747
		pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
L
Linus Torvalds 已提交
3748

3749 3750 3751 3752 3753 3754 3755 3756
		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
		 */
3757 3758 3759 3760 3761 3762 3763 3764 3765 3766 3767
		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).
		 */
3768 3769
		trace_mm_vmscan_kswapd_wake(pgdat->node_id, classzone_idx,
						alloc_order);
3770 3771 3772
		reclaim_order = balance_pgdat(pgdat, alloc_order, classzone_idx);
		if (reclaim_order < alloc_order)
			goto kswapd_try_sleep;
L
Linus Torvalds 已提交
3773
	}
3774

3775
	tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD);
3776
	current->reclaim_state = NULL;
3777

L
Linus Torvalds 已提交
3778 3779 3780 3781
	return 0;
}

/*
3782 3783 3784 3785 3786
 * A zone is low on free memory or too fragmented for high-order memory.  If
 * kswapd should reclaim (direct reclaim is deferred), wake it up for the zone's
 * pgdat.  It will wake up kcompactd after reclaiming memory.  If kswapd reclaim
 * has failed or is not needed, still wake up kcompactd if only compaction is
 * needed.
L
Linus Torvalds 已提交
3787
 */
3788 3789
void wakeup_kswapd(struct zone *zone, gfp_t gfp_flags, int order,
		   enum zone_type classzone_idx)
L
Linus Torvalds 已提交
3790 3791 3792
{
	pg_data_t *pgdat;

3793
	if (!managed_zone(zone))
L
Linus Torvalds 已提交
3794 3795
		return;

3796
	if (!cpuset_zone_allowed(zone, gfp_flags))
L
Linus Torvalds 已提交
3797
		return;
3798
	pgdat = zone->zone_pgdat;
3799 3800
	pgdat->kswapd_classzone_idx = kswapd_classzone_idx(pgdat,
							   classzone_idx);
3801
	pgdat->kswapd_order = max(pgdat->kswapd_order, order);
3802
	if (!waitqueue_active(&pgdat->kswapd_wait))
L
Linus Torvalds 已提交
3803
		return;
3804

3805 3806 3807 3808 3809 3810 3811 3812 3813 3814 3815 3816
	/* Hopeless node, leave it to direct reclaim if possible */
	if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES ||
	    pgdat_balanced(pgdat, order, classzone_idx)) {
		/*
		 * There may be plenty of free memory available, but it's too
		 * fragmented for high-order allocations.  Wake up kcompactd
		 * and rely on compaction_suitable() to determine if it's
		 * needed.  If it fails, it will defer subsequent attempts to
		 * ratelimit its work.
		 */
		if (!(gfp_flags & __GFP_DIRECT_RECLAIM))
			wakeup_kcompactd(pgdat, order, classzone_idx);
3817
		return;
3818
	}
3819

3820 3821
	trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, classzone_idx, order,
				      gfp_flags);
3822
	wake_up_interruptible(&pgdat->kswapd_wait);
L
Linus Torvalds 已提交
3823 3824
}

3825
#ifdef CONFIG_HIBERNATION
L
Linus Torvalds 已提交
3826
/*
3827
 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
3828 3829 3830 3831 3832
 * 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
3833
 */
3834
unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
L
Linus Torvalds 已提交
3835
{
3836 3837
	struct reclaim_state reclaim_state;
	struct scan_control sc = {
3838
		.nr_to_reclaim = nr_to_reclaim,
3839
		.gfp_mask = GFP_HIGHUSER_MOVABLE,
3840
		.reclaim_idx = MAX_NR_ZONES - 1,
3841
		.priority = DEF_PRIORITY,
3842
		.may_writepage = 1,
3843 3844
		.may_unmap = 1,
		.may_swap = 1,
3845
		.hibernation_mode = 1,
L
Linus Torvalds 已提交
3846
	};
3847
	struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3848 3849
	struct task_struct *p = current;
	unsigned long nr_reclaimed;
3850
	unsigned int noreclaim_flag;
L
Linus Torvalds 已提交
3851

3852
	fs_reclaim_acquire(sc.gfp_mask);
3853
	noreclaim_flag = memalloc_noreclaim_save();
3854 3855
	reclaim_state.reclaimed_slab = 0;
	p->reclaim_state = &reclaim_state;
3856

3857
	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3858

3859
	p->reclaim_state = NULL;
3860
	memalloc_noreclaim_restore(noreclaim_flag);
3861
	fs_reclaim_release(sc.gfp_mask);
3862

3863
	return nr_reclaimed;
L
Linus Torvalds 已提交
3864
}
3865
#endif /* CONFIG_HIBERNATION */
L
Linus Torvalds 已提交
3866 3867 3868 3869 3870

/* 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. */
3871
static int kswapd_cpu_online(unsigned int cpu)
L
Linus Torvalds 已提交
3872
{
3873
	int nid;
L
Linus Torvalds 已提交
3874

3875 3876 3877
	for_each_node_state(nid, N_MEMORY) {
		pg_data_t *pgdat = NODE_DATA(nid);
		const struct cpumask *mask;
3878

3879
		mask = cpumask_of_node(pgdat->node_id);
3880

3881 3882 3883
		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
3884
	}
3885
	return 0;
L
Linus Torvalds 已提交
3886 3887
}

3888 3889 3890 3891 3892 3893 3894 3895 3896 3897 3898 3899 3900 3901 3902
/*
 * 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 */
3903
		BUG_ON(system_state < SYSTEM_RUNNING);
3904 3905
		pr_err("Failed to start kswapd on node %d\n", nid);
		ret = PTR_ERR(pgdat->kswapd);
3906
		pgdat->kswapd = NULL;
3907 3908 3909 3910
	}
	return ret;
}

3911
/*
3912
 * Called by memory hotplug when all memory in a node is offlined.  Caller must
3913
 * hold mem_hotplug_begin/end().
3914 3915 3916 3917 3918
 */
void kswapd_stop(int nid)
{
	struct task_struct *kswapd = NODE_DATA(nid)->kswapd;

3919
	if (kswapd) {
3920
		kthread_stop(kswapd);
3921 3922
		NODE_DATA(nid)->kswapd = NULL;
	}
3923 3924
}

L
Linus Torvalds 已提交
3925 3926
static int __init kswapd_init(void)
{
3927
	int nid, ret;
3928

L
Linus Torvalds 已提交
3929
	swap_setup();
3930
	for_each_node_state(nid, N_MEMORY)
3931
 		kswapd_run(nid);
3932 3933 3934 3935
	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
3936 3937 3938 3939
	return 0;
}

module_init(kswapd_init)
3940 3941 3942

#ifdef CONFIG_NUMA
/*
3943
 * Node reclaim mode
3944
 *
3945
 * If non-zero call node_reclaim when the number of free pages falls below
3946 3947
 * the watermarks.
 */
3948
int node_reclaim_mode __read_mostly;
3949

3950
#define RECLAIM_OFF 0
3951
#define RECLAIM_ZONE (1<<0)	/* Run shrink_inactive_list on the zone */
3952
#define RECLAIM_WRITE (1<<1)	/* Writeout pages during reclaim */
3953
#define RECLAIM_UNMAP (1<<2)	/* Unmap pages during reclaim */
3954

3955
/*
3956
 * Priority for NODE_RECLAIM. This determines the fraction of pages
3957 3958 3959
 * of a node considered for each zone_reclaim. 4 scans 1/16th of
 * a zone.
 */
3960
#define NODE_RECLAIM_PRIORITY 4
3961

3962
/*
3963
 * Percentage of pages in a zone that must be unmapped for node_reclaim to
3964 3965 3966 3967
 * occur.
 */
int sysctl_min_unmapped_ratio = 1;

3968 3969 3970 3971 3972 3973
/*
 * 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;

3974
static inline unsigned long node_unmapped_file_pages(struct pglist_data *pgdat)
3975
{
3976 3977 3978
	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);
3979 3980 3981 3982 3983 3984 3985 3986 3987 3988

	/*
	 * 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 */
3989
static unsigned long node_pagecache_reclaimable(struct pglist_data *pgdat)
3990
{
3991 3992
	unsigned long nr_pagecache_reclaimable;
	unsigned long delta = 0;
3993 3994

	/*
3995
	 * If RECLAIM_UNMAP is set, then all file pages are considered
3996
	 * potentially reclaimable. Otherwise, we have to worry about
3997
	 * pages like swapcache and node_unmapped_file_pages() provides
3998 3999
	 * a better estimate
	 */
4000 4001
	if (node_reclaim_mode & RECLAIM_UNMAP)
		nr_pagecache_reclaimable = node_page_state(pgdat, NR_FILE_PAGES);
4002
	else
4003
		nr_pagecache_reclaimable = node_unmapped_file_pages(pgdat);
4004 4005

	/* If we can't clean pages, remove dirty pages from consideration */
4006 4007
	if (!(node_reclaim_mode & RECLAIM_WRITE))
		delta += node_page_state(pgdat, NR_FILE_DIRTY);
4008 4009 4010 4011 4012 4013 4014 4015

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

	return nr_pagecache_reclaimable - delta;
}

4016
/*
4017
 * Try to free up some pages from this node through reclaim.
4018
 */
4019
static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
4020
{
4021
	/* Minimum pages needed in order to stay on node */
4022
	const unsigned long nr_pages = 1 << order;
4023 4024
	struct task_struct *p = current;
	struct reclaim_state reclaim_state;
4025
	unsigned int noreclaim_flag;
4026
	struct scan_control sc = {
4027
		.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
4028
		.gfp_mask = current_gfp_context(gfp_mask),
4029
		.order = order,
4030 4031 4032
		.priority = NODE_RECLAIM_PRIORITY,
		.may_writepage = !!(node_reclaim_mode & RECLAIM_WRITE),
		.may_unmap = !!(node_reclaim_mode & RECLAIM_UNMAP),
4033
		.may_swap = 1,
4034
		.reclaim_idx = gfp_zone(gfp_mask),
4035
	};
4036 4037

	cond_resched();
4038
	fs_reclaim_acquire(sc.gfp_mask);
4039
	/*
4040
	 * We need to be able to allocate from the reserves for RECLAIM_UNMAP
4041
	 * and we also need to be able to write out pages for RECLAIM_WRITE
4042
	 * and RECLAIM_UNMAP.
4043
	 */
4044 4045
	noreclaim_flag = memalloc_noreclaim_save();
	p->flags |= PF_SWAPWRITE;
4046 4047
	reclaim_state.reclaimed_slab = 0;
	p->reclaim_state = &reclaim_state;
4048

4049
	if (node_pagecache_reclaimable(pgdat) > pgdat->min_unmapped_pages) {
4050
		/*
4051
		 * Free memory by calling shrink node with increasing
4052 4053 4054
		 * priorities until we have enough memory freed.
		 */
		do {
4055
			shrink_node(pgdat, &sc);
4056
		} while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
4057
	}
4058

4059
	p->reclaim_state = NULL;
4060 4061
	current->flags &= ~PF_SWAPWRITE;
	memalloc_noreclaim_restore(noreclaim_flag);
4062
	fs_reclaim_release(sc.gfp_mask);
4063
	return sc.nr_reclaimed >= nr_pages;
4064
}
4065

4066
int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
4067
{
4068
	int ret;
4069 4070

	/*
4071
	 * Node reclaim reclaims unmapped file backed pages and
4072
	 * slab pages if we are over the defined limits.
4073
	 *
4074 4075
	 * A small portion of unmapped file backed pages is needed for
	 * file I/O otherwise pages read by file I/O will be immediately
4076 4077
	 * thrown out if the node is overallocated. So we do not reclaim
	 * if less than a specified percentage of the node is used by
4078
	 * unmapped file backed pages.
4079
	 */
4080
	if (node_pagecache_reclaimable(pgdat) <= pgdat->min_unmapped_pages &&
4081
	    node_page_state(pgdat, NR_SLAB_RECLAIMABLE) <= pgdat->min_slab_pages)
4082
		return NODE_RECLAIM_FULL;
4083 4084

	/*
4085
	 * Do not scan if the allocation should not be delayed.
4086
	 */
4087
	if (!gfpflags_allow_blocking(gfp_mask) || (current->flags & PF_MEMALLOC))
4088
		return NODE_RECLAIM_NOSCAN;
4089 4090

	/*
4091
	 * Only run node reclaim on the local node or on nodes that do not
4092 4093 4094 4095
	 * have associated processors. This will favor the local processor
	 * over remote processors and spread off node memory allocations
	 * as wide as possible.
	 */
4096 4097
	if (node_state(pgdat->node_id, N_CPU) && pgdat->node_id != numa_node_id())
		return NODE_RECLAIM_NOSCAN;
4098

4099 4100
	if (test_and_set_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags))
		return NODE_RECLAIM_NOSCAN;
4101

4102 4103
	ret = __node_reclaim(pgdat, gfp_mask, order);
	clear_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags);
4104

4105 4106 4107
	if (!ret)
		count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);

4108
	return ret;
4109
}
4110
#endif
L
Lee Schermerhorn 已提交
4111 4112 4113 4114 4115 4116

/*
 * 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
4117
 * lists vs unevictable list.
L
Lee Schermerhorn 已提交
4118 4119
 *
 * Reasons page might not be evictable:
4120
 * (1) page's mapping marked unevictable
N
Nick Piggin 已提交
4121
 * (2) page is part of an mlocked VMA
4122
 *
L
Lee Schermerhorn 已提交
4123
 */
4124
int page_evictable(struct page *page)
L
Lee Schermerhorn 已提交
4125
{
4126 4127 4128 4129 4130 4131 4132
	int ret;

	/* Prevent address_space of inode and swap cache from being freed */
	rcu_read_lock();
	ret = !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
	rcu_read_unlock();
	return ret;
L
Lee Schermerhorn 已提交
4133
}
4134

4135
#ifdef CONFIG_SHMEM
4136
/**
4137 4138 4139
 * 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
4140
 *
4141
 * Checks pages for evictability and moves them to the appropriate lru list.
4142 4143
 *
 * This function is only used for SysV IPC SHM_UNLOCK.
4144
 */
4145
void check_move_unevictable_pages(struct page **pages, int nr_pages)
4146
{
4147
	struct lruvec *lruvec;
4148
	struct pglist_data *pgdat = NULL;
4149 4150 4151
	int pgscanned = 0;
	int pgrescued = 0;
	int i;
4152

4153 4154
	for (i = 0; i < nr_pages; i++) {
		struct page *page = pages[i];
4155
		struct pglist_data *pagepgdat = page_pgdat(page);
4156

4157
		pgscanned++;
4158 4159 4160 4161 4162
		if (pagepgdat != pgdat) {
			if (pgdat)
				spin_unlock_irq(&pgdat->lru_lock);
			pgdat = pagepgdat;
			spin_lock_irq(&pgdat->lru_lock);
4163
		}
4164
		lruvec = mem_cgroup_page_lruvec(page, pgdat);
4165

4166 4167
		if (!PageLRU(page) || !PageUnevictable(page))
			continue;
4168

4169
		if (page_evictable(page)) {
4170 4171
			enum lru_list lru = page_lru_base_type(page);

4172
			VM_BUG_ON_PAGE(PageActive(page), page);
4173
			ClearPageUnevictable(page);
4174 4175
			del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
			add_page_to_lru_list(page, lruvec, lru);
4176
			pgrescued++;
4177
		}
4178
	}
4179

4180
	if (pgdat) {
4181 4182
		__count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
		__count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
4183
		spin_unlock_irq(&pgdat->lru_lock);
4184 4185
	}
}
4186
#endif /* CONFIG_SHMEM */