vmscan.c 109.8 KB
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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.
 */

#include <linux/mm.h>
#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 <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 {
	/* Incremented by the number of inactive pages that were scanned */
	unsigned long nr_scanned;

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	/* Number of pages freed so far during a call to shrink_zones() */
	unsigned long nr_reclaimed;

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

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	unsigned long hibernation_mode;

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

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	/* Can mapped pages be reclaimed? */
	int may_unmap;
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	/* Can pages be swapped as part of reclaim? */
	int may_swap;

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

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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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	/*
	 * Nodemask of nodes allowed by the caller. If NULL, all nodes
	 * are scanned.
	 */
	nodemask_t	*nodemask;
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};

#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))

#ifdef ARCH_HAS_PREFETCH
#define prefetch_prev_lru_page(_page, _base, _field)			\
	do {								\
		if ((_page)->lru.prev != _base) {			\
			struct page *prev;				\
									\
			prev = lru_to_page(&(_page->lru));		\
			prefetch(&prev->_field);			\
		}							\
	} while (0)
#else
#define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
#endif

#ifdef ARCH_HAS_PREFETCHW
#define prefetchw_prev_lru_page(_page, _base, _field)			\
	do {								\
		if ((_page)->lru.prev != _base) {			\
			struct page *prev;				\
									\
			prev = lru_to_page(&(_page->lru));		\
			prefetchw(&prev->_field);			\
		}							\
	} while (0)
#else
#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
#endif

/*
 * From 0 .. 100.  Higher means more swappy.
 */
int vm_swappiness = 60;
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unsigned long vm_total_pages;	/* The total number of pages which the VM controls */
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static LIST_HEAD(shrinker_list);
static DECLARE_RWSEM(shrinker_rwsem);

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#ifdef CONFIG_MEMCG
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static bool global_reclaim(struct scan_control *sc)
{
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	return !sc->target_mem_cgroup;
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}
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#else
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static bool global_reclaim(struct scan_control *sc)
{
	return true;
}
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#endif

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static unsigned long zone_reclaimable_pages(struct zone *zone)
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{
	int nr;

	nr = zone_page_state(zone, NR_ACTIVE_FILE) +
	     zone_page_state(zone, NR_INACTIVE_FILE);

	if (get_nr_swap_pages() > 0)
		nr += zone_page_state(zone, NR_ACTIVE_ANON) +
		      zone_page_state(zone, NR_INACTIVE_ANON);

	return nr;
}

bool zone_reclaimable(struct zone *zone)
{
	return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
}

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static unsigned long get_lru_size(struct lruvec *lruvec, enum lru_list lru)
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{
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	if (!mem_cgroup_disabled())
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		return mem_cgroup_get_lru_size(lruvec, lru);
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	return zone_page_state(lruvec_zone(lruvec), NR_LRU_BASE + lru);
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}

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

	/*
	 * If we only have one possible node in the system anyway, save
	 * ourselves the trouble and disable NUMA aware behavior. This way we
	 * will save memory and some small loop time later.
	 */
	if (nr_node_ids == 1)
		shrinker->flags &= ~SHRINKER_NUMA_AWARE;

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

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

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	down_write(&shrinker_rwsem);
	list_add_tail(&shrinker->list, &shrinker_list);
	up_write(&shrinker_rwsem);
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	return 0;
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}
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EXPORT_SYMBOL(register_shrinker);
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/*
 * Remove one
 */
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void unregister_shrinker(struct shrinker *shrinker)
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{
	down_write(&shrinker_rwsem);
	list_del(&shrinker->list);
	up_write(&shrinker_rwsem);
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	kfree(shrinker->nr_deferred);
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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
shrink_slab_node(struct shrink_control *shrinkctl, struct shrinker *shrinker,
		 unsigned long nr_pages_scanned, unsigned long lru_pages)
{
	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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	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;
	delta = (4 * nr_pages_scanned) / shrinker->seeks;
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	delta *= freeable;
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	do_div(delta, lru_pages + 1);
	total_scan += delta;
	if (total_scan < 0) {
		printk(KERN_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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	}

	/*
	 * 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,
				nr_pages_scanned, lru_pages,
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				freeable, delta, total_scan);
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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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		ret = shrinker->scan_objects(shrinker, shrinkctl);
		if (ret == SHRINK_STOP)
			break;
		freed += ret;
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		count_vm_events(SLABS_SCANNED, nr_to_scan);
		total_scan -= nr_to_scan;
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		cond_resched();
	}

	/*
	 * move the unused scan count back into the shrinker in a
	 * manner that handles concurrent updates. If we exhausted the
	 * scan, there is no need to do an update.
	 */
	if (total_scan > 0)
		new_nr = atomic_long_add_return(total_scan,
						&shrinker->nr_deferred[nid]);
	else
		new_nr = atomic_long_read(&shrinker->nr_deferred[nid]);

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

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/*
 * Call the shrink functions to age shrinkable caches
 *
 * Here we assume it costs one seek to replace a lru page and that it also
 * takes a seek to recreate a cache object.  With this in mind we age equal
 * percentages of the lru and ageable caches.  This should balance the seeks
 * generated by these structures.
 *
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 * If the vm encountered mapped pages on the LRU it increase the pressure on
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 * slab to avoid swapping.
 *
 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
 *
 * `lru_pages' represents the number of on-LRU pages in all the zones which
 * are eligible for the caller's allocation attempt.  It is used for balancing
 * slab reclaim versus page reclaim.
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 *
 * Returns the number of slab objects which we shrunk.
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 */
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unsigned long shrink_slab(struct shrink_control *shrinkctl,
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			  unsigned long nr_pages_scanned,
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			  unsigned long lru_pages)
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{
	struct shrinker *shrinker;
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	unsigned long freed = 0;
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	if (nr_pages_scanned == 0)
		nr_pages_scanned = SWAP_CLUSTER_MAX;
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	if (!down_read_trylock(&shrinker_rwsem)) {
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		/*
		 * If we would return 0, our callers would understand that we
		 * have nothing else to shrink and give up trying. By returning
		 * 1 we keep it going and assume we'll be able to shrink next
		 * time.
		 */
		freed = 1;
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		goto out;
	}
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	list_for_each_entry(shrinker, &shrinker_list, list) {
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		if (!(shrinker->flags & SHRINKER_NUMA_AWARE)) {
			shrinkctl->nid = 0;
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			freed += shrink_slab_node(shrinkctl, shrinker,
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					nr_pages_scanned, lru_pages);
			continue;
		}

		for_each_node_mask(shrinkctl->nid, shrinkctl->nodes_to_scan) {
			if (node_online(shrinkctl->nid))
				freed += shrink_slab_node(shrinkctl, shrinker,
						nr_pages_scanned, lru_pages);
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		}
	}
	up_read(&shrinker_rwsem);
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out:
	cond_resched();
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	return freed;
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}

static inline int is_page_cache_freeable(struct page *page)
{
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	/*
	 * A freeable page cache page is referenced only by the caller
	 * that isolated the page, the page cache radix tree and
	 * optional buffer heads at page->private.
	 */
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	return page_count(page) - page_has_private(page) == 2;
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}

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static int may_write_to_queue(struct backing_dev_info *bdi,
			      struct scan_control *sc)
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{
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	if (current->flags & PF_SWAPWRITE)
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		return 1;
	if (!bdi_write_congested(bdi))
		return 1;
	if (bdi == current->backing_dev_info)
		return 1;
	return 0;
}

/*
 * We detected a synchronous write error writing a page out.  Probably
 * -ENOSPC.  We need to propagate that into the address_space for a subsequent
 * fsync(), msync() or close().
 *
 * The tricky part is that after writepage we cannot touch the mapping: nothing
 * prevents it from being freed up.  But we have a ref on the page and once
 * that page is locked, the mapping is pinned.
 *
 * We're allowed to run sleeping lock_page() here because we know the caller has
 * __GFP_FS.
 */
static void handle_write_error(struct address_space *mapping,
				struct page *page, int error)
{
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	lock_page(page);
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	if (page_mapping(page) == mapping)
		mapping_set_error(mapping, error);
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	unlock_page(page);
}

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/* possible outcome of pageout() */
typedef enum {
	/* failed to write page out, page is locked */
	PAGE_KEEP,
	/* move page to the active list, page is locked */
	PAGE_ACTIVATE,
	/* page has been sent to the disk successfully, page is unlocked */
	PAGE_SUCCESS,
	/* page is clean and locked */
	PAGE_CLEAN,
} pageout_t;

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/*
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 * pageout is called by shrink_page_list() for each dirty page.
 * Calls ->writepage().
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 */
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static pageout_t pageout(struct page *page, struct address_space *mapping,
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			 struct scan_control *sc)
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{
	/*
	 * If the page is dirty, only perform writeback if that write
	 * will be non-blocking.  To prevent this allocation from being
	 * stalled by pagecache activity.  But note that there may be
	 * stalls if we need to run get_block().  We could test
	 * PagePrivate for that.
	 *
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	 * If this process is currently in __generic_file_aio_write() against
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	 * 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.
		 */
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		if (page_has_private(page)) {
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			if (try_to_free_buffers(page)) {
				ClearPageDirty(page);
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				printk("%s: orphaned page\n", __func__);
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				return PAGE_CLEAN;
			}
		}
		return PAGE_KEEP;
	}
	if (mapping->a_ops->writepage == NULL)
		return PAGE_ACTIVATE;
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	if (!may_write_to_queue(mapping->backing_dev_info, sc))
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		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,
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			.range_start = 0,
			.range_end = LLONG_MAX,
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			.for_reclaim = 1,
		};

		SetPageReclaim(page);
		res = mapping->a_ops->writepage(page, &wbc);
		if (res < 0)
			handle_write_error(mapping, page, res);
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		if (res == AOP_WRITEPAGE_ACTIVATE) {
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			ClearPageReclaim(page);
			return PAGE_ACTIVATE;
		}
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		if (!PageWriteback(page)) {
			/* synchronous write or broken a_ops? */
			ClearPageReclaim(page);
		}
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		trace_mm_vmscan_writepage(page, trace_reclaim_flags(page));
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		inc_zone_page_state(page, NR_VMSCAN_WRITE);
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		return PAGE_SUCCESS;
	}

	return PAGE_CLEAN;
}

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/*
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 * Same as remove_mapping, but if the page is removed from the mapping, it
 * gets returned with a refcount of 0.
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 */
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static int __remove_mapping(struct address_space *mapping, struct page *page,
			    bool reclaimed)
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{
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	BUG_ON(!PageLocked(page));
	BUG_ON(mapping != page_mapping(page));
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	spin_lock_irq(&mapping->tree_lock);
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	/*
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	 * The non racy check for a busy page.
	 *
	 * Must be careful with the order of the tests. When someone has
	 * a ref to the page, it may be possible that they dirty it then
	 * drop the reference. So if PageDirty is tested before page_count
	 * here, then the following race may occur:
	 *
	 * get_user_pages(&page);
	 * [user mapping goes away]
	 * write_to(page);
	 *				!PageDirty(page)    [good]
	 * SetPageDirty(page);
	 * put_page(page);
	 *				!page_count(page)   [good, discard it]
	 *
	 * [oops, our write_to data is lost]
	 *
	 * Reversing the order of the tests ensures such a situation cannot
	 * escape unnoticed. The smp_rmb is needed to ensure the page->flags
	 * load is not satisfied before that of page->_count.
	 *
	 * Note that if SetPageDirty is always performed via set_page_dirty,
	 * and thus under tree_lock, then this ordering is not required.
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	 */
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	if (!page_freeze_refs(page, 2))
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		goto cannot_free;
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	/* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
	if (unlikely(PageDirty(page))) {
		page_unfreeze_refs(page, 2);
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		goto cannot_free;
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	}
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	if (PageSwapCache(page)) {
		swp_entry_t swap = { .val = page_private(page) };
		__delete_from_swap_cache(page);
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		spin_unlock_irq(&mapping->tree_lock);
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		swapcache_free(swap, page);
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	} else {
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		void (*freepage)(struct page *);
573
		void *shadow = NULL;
574 575

		freepage = mapping->a_ops->freepage;
576 577 578 579 580 581 582 583 584 585 586 587 588 589
		/*
		 * Remember a shadow entry for reclaimed file cache in
		 * order to detect refaults, thus thrashing, later on.
		 *
		 * But don't store shadows in an address space that is
		 * already exiting.  This is not just an optizimation,
		 * inode reclaim needs to empty out the radix tree or
		 * the nodes are lost.  Don't plant shadows behind its
		 * back.
		 */
		if (reclaimed && page_is_file_cache(page) &&
		    !mapping_exiting(mapping))
			shadow = workingset_eviction(mapping, page);
		__delete_from_page_cache(page, shadow);
N
Nick Piggin 已提交
590
		spin_unlock_irq(&mapping->tree_lock);
591
		mem_cgroup_uncharge_cache_page(page);
592 593 594

		if (freepage != NULL)
			freepage(page);
595 596 597 598 599
	}

	return 1;

cannot_free:
N
Nick Piggin 已提交
600
	spin_unlock_irq(&mapping->tree_lock);
601 602 603
	return 0;
}

N
Nick Piggin 已提交
604 605 606 607 608 609 610 611
/*
 * 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)
{
612
	if (__remove_mapping(mapping, page, false)) {
N
Nick Piggin 已提交
613 614 615 616 617 618 619 620 621 622 623
		/*
		 * Unfreezing the refcount with 1 rather than 2 effectively
		 * drops the pagecache ref for us without requiring another
		 * atomic operation.
		 */
		page_unfreeze_refs(page, 1);
		return 1;
	}
	return 0;
}

L
Lee Schermerhorn 已提交
624 625 626 627 628 629 630 631 632 633 634
/**
 * 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)
{
635
	bool is_unevictable;
636
	int was_unevictable = PageUnevictable(page);
L
Lee Schermerhorn 已提交
637

638
	VM_BUG_ON_PAGE(PageLRU(page), page);
L
Lee Schermerhorn 已提交
639 640 641 642

redo:
	ClearPageUnevictable(page);

643
	if (page_evictable(page)) {
L
Lee Schermerhorn 已提交
644 645 646 647 648 649
		/*
		 * For evictable pages, we can use the cache.
		 * In event of a race, worst case is we end up with an
		 * unevictable page on [in]active list.
		 * We know how to handle that.
		 */
650
		is_unevictable = false;
651
		lru_cache_add(page);
L
Lee Schermerhorn 已提交
652 653 654 655 656
	} else {
		/*
		 * Put unevictable pages directly on zone's unevictable
		 * list.
		 */
657
		is_unevictable = true;
L
Lee Schermerhorn 已提交
658
		add_page_to_unevictable_list(page);
659
		/*
660 661 662
		 * When racing with an mlock or AS_UNEVICTABLE clearing
		 * (page is unlocked) make sure that if the other thread
		 * does not observe our setting of PG_lru and fails
663
		 * isolation/check_move_unevictable_pages,
664
		 * we see PG_mlocked/AS_UNEVICTABLE cleared below and move
665 666
		 * the page back to the evictable list.
		 *
667
		 * The other side is TestClearPageMlocked() or shmem_lock().
668 669
		 */
		smp_mb();
L
Lee Schermerhorn 已提交
670 671 672 673 674 675 676
	}

	/*
	 * page's status can change while we move it among lru. If an evictable
	 * page is on unevictable list, it never be freed. To avoid that,
	 * check after we added it to the list, again.
	 */
677
	if (is_unevictable && page_evictable(page)) {
L
Lee Schermerhorn 已提交
678 679 680 681 682 683 684 685 686 687
		if (!isolate_lru_page(page)) {
			put_page(page);
			goto redo;
		}
		/* This means someone else dropped this page from LRU
		 * So, it will be freed or putback to LRU again. There is
		 * nothing to do here.
		 */
	}

688
	if (was_unevictable && !is_unevictable)
689
		count_vm_event(UNEVICTABLE_PGRESCUED);
690
	else if (!was_unevictable && is_unevictable)
691 692
		count_vm_event(UNEVICTABLE_PGCULLED);

L
Lee Schermerhorn 已提交
693 694 695
	put_page(page);		/* drop ref from isolate */
}

696 697 698
enum page_references {
	PAGEREF_RECLAIM,
	PAGEREF_RECLAIM_CLEAN,
699
	PAGEREF_KEEP,
700 701 702 703 704 705
	PAGEREF_ACTIVATE,
};

static enum page_references page_check_references(struct page *page,
						  struct scan_control *sc)
{
706
	int referenced_ptes, referenced_page;
707 708
	unsigned long vm_flags;

709 710
	referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
					  &vm_flags);
711
	referenced_page = TestClearPageReferenced(page);
712 713 714 715 716 717 718 719

	/*
	 * 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;

720
	if (referenced_ptes) {
721
		if (PageSwapBacked(page))
722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738
			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);

739
		if (referenced_page || referenced_ptes > 1)
740 741
			return PAGEREF_ACTIVATE;

742 743 744 745 746 747
		/*
		 * Activate file-backed executable pages after first usage.
		 */
		if (vm_flags & VM_EXEC)
			return PAGEREF_ACTIVATE;

748 749
		return PAGEREF_KEEP;
	}
750 751

	/* Reclaim if clean, defer dirty pages to writeback */
752
	if (referenced_page && !PageSwapBacked(page))
753 754 755
		return PAGEREF_RECLAIM_CLEAN;

	return PAGEREF_RECLAIM;
756 757
}

758 759 760 761
/* Check if a page is dirty or under writeback */
static void page_check_dirty_writeback(struct page *page,
				       bool *dirty, bool *writeback)
{
762 763
	struct address_space *mapping;

764 765 766 767 768 769 770 771 772 773 774 775 776
	/*
	 * Anonymous pages are not handled by flushers and must be written
	 * from reclaim context. Do not stall reclaim based on them
	 */
	if (!page_is_file_cache(page)) {
		*dirty = false;
		*writeback = false;
		return;
	}

	/* By default assume that the page flags are accurate */
	*dirty = PageDirty(page);
	*writeback = PageWriteback(page);
777 778 779 780 781 782 783 784

	/* 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);
785 786
}

L
Linus Torvalds 已提交
787
/*
A
Andrew Morton 已提交
788
 * shrink_page_list() returns the number of reclaimed pages
L
Linus Torvalds 已提交
789
 */
A
Andrew Morton 已提交
790
static unsigned long shrink_page_list(struct list_head *page_list,
791
				      struct zone *zone,
792
				      struct scan_control *sc,
793
				      enum ttu_flags ttu_flags,
794
				      unsigned long *ret_nr_dirty,
795
				      unsigned long *ret_nr_unqueued_dirty,
796
				      unsigned long *ret_nr_congested,
797
				      unsigned long *ret_nr_writeback,
798
				      unsigned long *ret_nr_immediate,
799
				      bool force_reclaim)
L
Linus Torvalds 已提交
800 801
{
	LIST_HEAD(ret_pages);
802
	LIST_HEAD(free_pages);
L
Linus Torvalds 已提交
803
	int pgactivate = 0;
804
	unsigned long nr_unqueued_dirty = 0;
805 806
	unsigned long nr_dirty = 0;
	unsigned long nr_congested = 0;
807
	unsigned long nr_reclaimed = 0;
808
	unsigned long nr_writeback = 0;
809
	unsigned long nr_immediate = 0;
L
Linus Torvalds 已提交
810 811 812

	cond_resched();

813
	mem_cgroup_uncharge_start();
L
Linus Torvalds 已提交
814 815 816 817
	while (!list_empty(page_list)) {
		struct address_space *mapping;
		struct page *page;
		int may_enter_fs;
818
		enum page_references references = PAGEREF_RECLAIM_CLEAN;
819
		bool dirty, writeback;
L
Linus Torvalds 已提交
820 821 822 823 824 825

		cond_resched();

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

N
Nick Piggin 已提交
826
		if (!trylock_page(page))
L
Linus Torvalds 已提交
827 828
			goto keep;

829 830
		VM_BUG_ON_PAGE(PageActive(page), page);
		VM_BUG_ON_PAGE(page_zone(page) != zone, page);
L
Linus Torvalds 已提交
831 832

		sc->nr_scanned++;
833

834
		if (unlikely(!page_evictable(page)))
N
Nick Piggin 已提交
835
			goto cull_mlocked;
L
Lee Schermerhorn 已提交
836

837
		if (!sc->may_unmap && page_mapped(page))
838 839
			goto keep_locked;

L
Linus Torvalds 已提交
840 841 842 843
		/* Double the slab pressure for mapped and swapcache pages */
		if (page_mapped(page) || PageSwapCache(page))
			sc->nr_scanned++;

844 845 846
		may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
			(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));

847 848 849 850 851 852 853 854 855 856 857 858 859
		/*
		 * The number of dirty pages determines if a zone is marked
		 * reclaim_congested which affects wait_iff_congested. kswapd
		 * will stall and start writing pages if the tail of the LRU
		 * is all dirty unqueued pages.
		 */
		page_check_dirty_writeback(page, &dirty, &writeback);
		if (dirty || writeback)
			nr_dirty++;

		if (dirty && !writeback)
			nr_unqueued_dirty++;

860 861 862 863 864 865
		/*
		 * 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.
		 */
866
		mapping = page_mapping(page);
867 868
		if ((mapping && bdi_write_congested(mapping->backing_dev_info)) ||
		    (writeback && PageReclaim(page)))
869 870
			nr_congested++;

871 872 873 874 875 876 877 878 879 880 881
		/*
		 * 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
882 883
		 *    note that the LRU is being scanned too quickly and the
		 *    caller can stall after page list has been processed.
884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907
		 *
		 * 2) Global reclaim encounters a page, memcg encounters a
		 *    page that is not marked for immediate reclaim or
		 *    the caller does not have __GFP_IO. In this case mark
		 *    the page for immediate reclaim and continue scanning.
		 *
		 *    __GFP_IO is checked  because a loop driver thread might
		 *    enter reclaim, and deadlock if it waits on a page for
		 *    which it is needed to do the write (loop masks off
		 *    __GFP_IO|__GFP_FS for this reason); but more thought
		 *    would probably show more reasons.
		 *
		 *    Don't require __GFP_FS, since we're not going into the
		 *    FS, just waiting on its writeback completion. Worryingly,
		 *    ext4 gfs2 and xfs allocate pages with
		 *    grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so testing
		 *    may_enter_fs here is liable to OOM on them.
		 *
		 * 3) memcg encounters a page that is not already marked
		 *    PageReclaim. memcg does not have any dirty pages
		 *    throttling so we could easily OOM just because too many
		 *    pages are in writeback and there is nothing else to
		 *    reclaim. Wait for the writeback to complete.
		 */
908
		if (PageWriteback(page)) {
909 910 911 912
			/* Case 1 above */
			if (current_is_kswapd() &&
			    PageReclaim(page) &&
			    zone_is_reclaim_writeback(zone)) {
913 914
				nr_immediate++;
				goto keep_locked;
915 916 917

			/* Case 2 above */
			} else if (global_reclaim(sc) ||
918 919 920 921 922 923 924 925 926 927 928 929 930
			    !PageReclaim(page) || !(sc->gfp_mask & __GFP_IO)) {
				/*
				 * 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);
931
				nr_writeback++;
932

933
				goto keep_locked;
934 935 936 937

			/* Case 3 above */
			} else {
				wait_on_page_writeback(page);
938
			}
939
		}
L
Linus Torvalds 已提交
940

941 942 943
		if (!force_reclaim)
			references = page_check_references(page, sc);

944 945
		switch (references) {
		case PAGEREF_ACTIVATE:
L
Linus Torvalds 已提交
946
			goto activate_locked;
947 948
		case PAGEREF_KEEP:
			goto keep_locked;
949 950 951 952
		case PAGEREF_RECLAIM:
		case PAGEREF_RECLAIM_CLEAN:
			; /* try to reclaim the page below */
		}
L
Linus Torvalds 已提交
953 954 955 956 957

		/*
		 * Anonymous process memory has backing store?
		 * Try to allocate it some swap space here.
		 */
N
Nick Piggin 已提交
958
		if (PageAnon(page) && !PageSwapCache(page)) {
959 960
			if (!(sc->gfp_mask & __GFP_IO))
				goto keep_locked;
961
			if (!add_to_swap(page, page_list))
L
Linus Torvalds 已提交
962
				goto activate_locked;
963
			may_enter_fs = 1;
L
Linus Torvalds 已提交
964

965 966 967
			/* Adding to swap updated mapping */
			mapping = page_mapping(page);
		}
L
Linus Torvalds 已提交
968 969 970 971 972 973

		/*
		 * The page is mapped into the page tables of one or more
		 * processes. Try to unmap it here.
		 */
		if (page_mapped(page) && mapping) {
974
			switch (try_to_unmap(page, ttu_flags)) {
L
Linus Torvalds 已提交
975 976 977 978
			case SWAP_FAIL:
				goto activate_locked;
			case SWAP_AGAIN:
				goto keep_locked;
N
Nick Piggin 已提交
979 980
			case SWAP_MLOCK:
				goto cull_mlocked;
L
Linus Torvalds 已提交
981 982 983 984 985 986
			case SWAP_SUCCESS:
				; /* try to free the page below */
			}
		}

		if (PageDirty(page)) {
987 988
			/*
			 * Only kswapd can writeback filesystem pages to
989 990
			 * avoid risk of stack overflow but only writeback
			 * if many dirty pages have been encountered.
991
			 */
992
			if (page_is_file_cache(page) &&
993
					(!current_is_kswapd() ||
994
					 !zone_is_reclaim_dirty(zone))) {
995 996 997 998 999 1000 1001 1002 1003
				/*
				 * Immediately reclaim when written back.
				 * Similar in principal to deactivate_page()
				 * except we already have the page isolated
				 * and know it's dirty
				 */
				inc_zone_page_state(page, NR_VMSCAN_IMMEDIATE);
				SetPageReclaim(page);

1004 1005 1006
				goto keep_locked;
			}

1007
			if (references == PAGEREF_RECLAIM_CLEAN)
L
Linus Torvalds 已提交
1008
				goto keep_locked;
1009
			if (!may_enter_fs)
L
Linus Torvalds 已提交
1010
				goto keep_locked;
1011
			if (!sc->may_writepage)
L
Linus Torvalds 已提交
1012 1013 1014
				goto keep_locked;

			/* Page is dirty, try to write it out here */
1015
			switch (pageout(page, mapping, sc)) {
L
Linus Torvalds 已提交
1016 1017 1018 1019 1020
			case PAGE_KEEP:
				goto keep_locked;
			case PAGE_ACTIVATE:
				goto activate_locked;
			case PAGE_SUCCESS:
1021
				if (PageWriteback(page))
1022
					goto keep;
1023
				if (PageDirty(page))
L
Linus Torvalds 已提交
1024
					goto keep;
1025

L
Linus Torvalds 已提交
1026 1027 1028 1029
				/*
				 * A synchronous write - probably a ramdisk.  Go
				 * ahead and try to reclaim the page.
				 */
N
Nick Piggin 已提交
1030
				if (!trylock_page(page))
L
Linus Torvalds 已提交
1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049
					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
1050
		 * will do this, as well as the blockdev mapping.
L
Linus Torvalds 已提交
1051 1052 1053 1054 1055 1056 1057 1058 1059 1060
		 * 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.
		 */
1061
		if (page_has_private(page)) {
L
Linus Torvalds 已提交
1062 1063
			if (!try_to_release_page(page, sc->gfp_mask))
				goto activate_locked;
N
Nick Piggin 已提交
1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079
			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
1080 1081
		}

1082
		if (!mapping || !__remove_mapping(mapping, page, true))
1083
			goto keep_locked;
L
Linus Torvalds 已提交
1084

N
Nick Piggin 已提交
1085 1086 1087 1088 1089 1090 1091 1092
		/*
		 * At this point, we have no other references and there is
		 * no way to pick any more up (removed from LRU, removed
		 * from pagecache). Can use non-atomic bitops now (and
		 * we obviously don't have to worry about waking up a process
		 * waiting on the page lock, because there are no references.
		 */
		__clear_page_locked(page);
N
Nick Piggin 已提交
1093
free_it:
1094
		nr_reclaimed++;
1095 1096 1097 1098 1099 1100

		/*
		 * Is there need to periodically free_page_list? It would
		 * appear not as the counts should be low
		 */
		list_add(&page->lru, &free_pages);
L
Linus Torvalds 已提交
1101 1102
		continue;

N
Nick Piggin 已提交
1103
cull_mlocked:
1104 1105
		if (PageSwapCache(page))
			try_to_free_swap(page);
N
Nick Piggin 已提交
1106 1107 1108 1109
		unlock_page(page);
		putback_lru_page(page);
		continue;

L
Linus Torvalds 已提交
1110
activate_locked:
1111 1112
		/* Not a candidate for swapping, so reclaim swap space. */
		if (PageSwapCache(page) && vm_swap_full())
1113
			try_to_free_swap(page);
1114
		VM_BUG_ON_PAGE(PageActive(page), page);
L
Linus Torvalds 已提交
1115 1116 1117 1118 1119 1120
		SetPageActive(page);
		pgactivate++;
keep_locked:
		unlock_page(page);
keep:
		list_add(&page->lru, &ret_pages);
1121
		VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page);
L
Linus Torvalds 已提交
1122
	}
1123

1124
	free_hot_cold_page_list(&free_pages, 1);
1125

L
Linus Torvalds 已提交
1126
	list_splice(&ret_pages, page_list);
1127
	count_vm_events(PGACTIVATE, pgactivate);
1128
	mem_cgroup_uncharge_end();
1129 1130
	*ret_nr_dirty += nr_dirty;
	*ret_nr_congested += nr_congested;
1131
	*ret_nr_unqueued_dirty += nr_unqueued_dirty;
1132
	*ret_nr_writeback += nr_writeback;
1133
	*ret_nr_immediate += nr_immediate;
1134
	return nr_reclaimed;
L
Linus Torvalds 已提交
1135 1136
}

1137 1138 1139 1140 1141 1142 1143 1144
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,
	};
1145
	unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5;
1146 1147 1148 1149
	struct page *page, *next;
	LIST_HEAD(clean_pages);

	list_for_each_entry_safe(page, next, page_list, lru) {
1150 1151
		if (page_is_file_cache(page) && !PageDirty(page) &&
		    !isolated_balloon_page(page)) {
1152 1153 1154 1155 1156 1157
			ClearPageActive(page);
			list_move(&page->lru, &clean_pages);
		}
	}

	ret = shrink_page_list(&clean_pages, zone, &sc,
1158 1159
			TTU_UNMAP|TTU_IGNORE_ACCESS,
			&dummy1, &dummy2, &dummy3, &dummy4, &dummy5, true);
1160
	list_splice(&clean_pages, page_list);
1161
	mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret);
1162 1163 1164
	return ret;
}

A
Andy Whitcroft 已提交
1165 1166 1167 1168 1169 1170 1171 1172 1173 1174
/*
 * 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.
 */
1175
int __isolate_lru_page(struct page *page, isolate_mode_t mode)
A
Andy Whitcroft 已提交
1176 1177 1178 1179 1180 1181 1182
{
	int ret = -EINVAL;

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

M
Minchan Kim 已提交
1183 1184
	/* Compaction should not handle unevictable pages but CMA can do so */
	if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
L
Lee Schermerhorn 已提交
1185 1186
		return ret;

A
Andy Whitcroft 已提交
1187
	ret = -EBUSY;
K
KAMEZAWA Hiroyuki 已提交
1188

1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221
	/*
	 * To minimise LRU disruption, the caller can indicate that it only
	 * wants to isolate pages it will be able to operate on without
	 * blocking - clean pages for the most part.
	 *
	 * ISOLATE_CLEAN means that only clean pages should be isolated. This
	 * is used by reclaim when it is cannot write to backing storage
	 *
	 * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
	 * that it is possible to migrate without blocking
	 */
	if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) {
		/* All the caller can do on PageWriteback is block */
		if (PageWriteback(page))
			return ret;

		if (PageDirty(page)) {
			struct address_space *mapping;

			/* ISOLATE_CLEAN means only clean pages */
			if (mode & ISOLATE_CLEAN)
				return ret;

			/*
			 * Only pages without mappings or that have a
			 * ->migratepage callback are possible to migrate
			 * without blocking
			 */
			mapping = page_mapping(page);
			if (mapping && !mapping->a_ops->migratepage)
				return ret;
		}
	}
1222

1223 1224 1225
	if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
		return ret;

A
Andy Whitcroft 已提交
1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238
	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;
}

L
Linus Torvalds 已提交
1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249
/*
 * zone->lru_lock is heavily contended.  Some of the functions that
 * shrink the lists perform better by taking out a batch of pages
 * and working on them outside the LRU lock.
 *
 * For pagecache intensive workloads, this function is the hottest
 * spot in the kernel (apart from copy_*_user functions).
 *
 * Appropriate locks must be held before calling this function.
 *
 * @nr_to_scan:	The number of pages to look through on the list.
1250
 * @lruvec:	The LRU vector to pull pages from.
L
Linus Torvalds 已提交
1251
 * @dst:	The temp list to put pages on to.
H
Hugh Dickins 已提交
1252
 * @nr_scanned:	The number of pages that were scanned.
1253
 * @sc:		The scan_control struct for this reclaim session
A
Andy Whitcroft 已提交
1254
 * @mode:	One of the LRU isolation modes
1255
 * @lru:	LRU list id for isolating
L
Linus Torvalds 已提交
1256 1257 1258
 *
 * returns how many pages were moved onto *@dst.
 */
1259
static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1260
		struct lruvec *lruvec, struct list_head *dst,
1261
		unsigned long *nr_scanned, struct scan_control *sc,
1262
		isolate_mode_t mode, enum lru_list lru)
L
Linus Torvalds 已提交
1263
{
H
Hugh Dickins 已提交
1264
	struct list_head *src = &lruvec->lists[lru];
1265
	unsigned long nr_taken = 0;
1266
	unsigned long scan;
L
Linus Torvalds 已提交
1267

1268
	for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
A
Andy Whitcroft 已提交
1269
		struct page *page;
1270
		int nr_pages;
A
Andy Whitcroft 已提交
1271

L
Linus Torvalds 已提交
1272 1273 1274
		page = lru_to_page(src);
		prefetchw_prev_lru_page(page, src, flags);

1275
		VM_BUG_ON_PAGE(!PageLRU(page), page);
N
Nick Piggin 已提交
1276

1277
		switch (__isolate_lru_page(page, mode)) {
A
Andy Whitcroft 已提交
1278
		case 0:
1279 1280
			nr_pages = hpage_nr_pages(page);
			mem_cgroup_update_lru_size(lruvec, lru, -nr_pages);
A
Andy Whitcroft 已提交
1281
			list_move(&page->lru, dst);
1282
			nr_taken += nr_pages;
A
Andy Whitcroft 已提交
1283 1284 1285 1286 1287 1288
			break;

		case -EBUSY:
			/* else it is being freed elsewhere */
			list_move(&page->lru, src);
			continue;
1289

A
Andy Whitcroft 已提交
1290 1291 1292
		default:
			BUG();
		}
L
Linus Torvalds 已提交
1293 1294
	}

H
Hugh Dickins 已提交
1295
	*nr_scanned = scan;
H
Hugh Dickins 已提交
1296 1297
	trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
				    nr_taken, mode, is_file_lru(lru));
L
Linus Torvalds 已提交
1298 1299 1300
	return nr_taken;
}

1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311
/**
 * 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
1312 1313 1314
 * 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.
1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329
 *
 * The vmstat statistic corresponding to the list on which the page was
 * found will be decremented.
 *
 * Restrictions:
 * (1) Must be called with an elevated refcount on the page. This is a
 *     fundamentnal difference from isolate_lru_pages (which is called
 *     without a stable reference).
 * (2) the lru_lock must not be held.
 * (3) interrupts must be enabled.
 */
int isolate_lru_page(struct page *page)
{
	int ret = -EBUSY;

1330
	VM_BUG_ON_PAGE(!page_count(page), page);
1331

1332 1333
	if (PageLRU(page)) {
		struct zone *zone = page_zone(page);
1334
		struct lruvec *lruvec;
1335 1336

		spin_lock_irq(&zone->lru_lock);
1337
		lruvec = mem_cgroup_page_lruvec(page, zone);
1338
		if (PageLRU(page)) {
L
Lee Schermerhorn 已提交
1339
			int lru = page_lru(page);
1340
			get_page(page);
1341
			ClearPageLRU(page);
1342 1343
			del_page_from_lru_list(page, lruvec, lru);
			ret = 0;
1344 1345 1346 1347 1348 1349
		}
		spin_unlock_irq(&zone->lru_lock);
	}
	return ret;
}

1350
/*
F
Fengguang Wu 已提交
1351 1352 1353 1354 1355
 * 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.
1356 1357 1358 1359 1360 1361 1362 1363 1364
 */
static int too_many_isolated(struct zone *zone, int file,
		struct scan_control *sc)
{
	unsigned long inactive, isolated;

	if (current_is_kswapd())
		return 0;

1365
	if (!global_reclaim(sc))
1366 1367 1368 1369 1370 1371 1372 1373 1374 1375
		return 0;

	if (file) {
		inactive = zone_page_state(zone, NR_INACTIVE_FILE);
		isolated = zone_page_state(zone, NR_ISOLATED_FILE);
	} else {
		inactive = zone_page_state(zone, NR_INACTIVE_ANON);
		isolated = zone_page_state(zone, NR_ISOLATED_ANON);
	}

1376 1377 1378 1379 1380 1381 1382 1383
	/*
	 * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they
	 * won't get blocked by normal direct-reclaimers, forming a circular
	 * deadlock.
	 */
	if ((sc->gfp_mask & GFP_IOFS) == GFP_IOFS)
		inactive >>= 3;

1384 1385 1386
	return isolated > inactive;
}

1387
static noinline_for_stack void
H
Hugh Dickins 已提交
1388
putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
1389
{
1390 1391
	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
	struct zone *zone = lruvec_zone(lruvec);
1392
	LIST_HEAD(pages_to_free);
1393 1394 1395 1396 1397

	/*
	 * Put back any unfreeable pages.
	 */
	while (!list_empty(page_list)) {
1398
		struct page *page = lru_to_page(page_list);
1399
		int lru;
1400

1401
		VM_BUG_ON_PAGE(PageLRU(page), page);
1402
		list_del(&page->lru);
1403
		if (unlikely(!page_evictable(page))) {
1404 1405 1406 1407 1408
			spin_unlock_irq(&zone->lru_lock);
			putback_lru_page(page);
			spin_lock_irq(&zone->lru_lock);
			continue;
		}
1409 1410 1411

		lruvec = mem_cgroup_page_lruvec(page, zone);

1412
		SetPageLRU(page);
1413
		lru = page_lru(page);
1414 1415
		add_page_to_lru_list(page, lruvec, lru);

1416 1417
		if (is_active_lru(lru)) {
			int file = is_file_lru(lru);
1418 1419
			int numpages = hpage_nr_pages(page);
			reclaim_stat->recent_rotated[file] += numpages;
1420
		}
1421 1422 1423
		if (put_page_testzero(page)) {
			__ClearPageLRU(page);
			__ClearPageActive(page);
1424
			del_page_from_lru_list(page, lruvec, lru);
1425 1426 1427 1428 1429 1430 1431

			if (unlikely(PageCompound(page))) {
				spin_unlock_irq(&zone->lru_lock);
				(*get_compound_page_dtor(page))(page);
				spin_lock_irq(&zone->lru_lock);
			} else
				list_add(&page->lru, &pages_to_free);
1432 1433 1434
		}
	}

1435 1436 1437 1438
	/*
	 * To save our caller's stack, now use input list for pages to free.
	 */
	list_splice(&pages_to_free, page_list);
1439 1440
}

1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453
/*
 * 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
1454
/*
A
Andrew Morton 已提交
1455 1456
 * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
 * of reclaimed pages
L
Linus Torvalds 已提交
1457
 */
1458
static noinline_for_stack unsigned long
1459
shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1460
		     struct scan_control *sc, enum lru_list lru)
L
Linus Torvalds 已提交
1461 1462
{
	LIST_HEAD(page_list);
1463
	unsigned long nr_scanned;
1464
	unsigned long nr_reclaimed = 0;
1465
	unsigned long nr_taken;
1466 1467
	unsigned long nr_dirty = 0;
	unsigned long nr_congested = 0;
1468
	unsigned long nr_unqueued_dirty = 0;
1469
	unsigned long nr_writeback = 0;
1470
	unsigned long nr_immediate = 0;
1471
	isolate_mode_t isolate_mode = 0;
1472
	int file = is_file_lru(lru);
1473 1474
	struct zone *zone = lruvec_zone(lruvec);
	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1475

1476
	while (unlikely(too_many_isolated(zone, file, sc))) {
1477
		congestion_wait(BLK_RW_ASYNC, HZ/10);
1478 1479 1480 1481 1482 1483

		/* 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
1484
	lru_add_drain();
1485 1486

	if (!sc->may_unmap)
1487
		isolate_mode |= ISOLATE_UNMAPPED;
1488
	if (!sc->may_writepage)
1489
		isolate_mode |= ISOLATE_CLEAN;
1490

L
Linus Torvalds 已提交
1491
	spin_lock_irq(&zone->lru_lock);
1492

1493 1494
	nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
				     &nr_scanned, sc, isolate_mode, lru);
1495 1496 1497 1498

	__mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);

1499
	if (global_reclaim(sc)) {
1500 1501
		zone->pages_scanned += nr_scanned;
		if (current_is_kswapd())
H
Hugh Dickins 已提交
1502
			__count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scanned);
1503
		else
H
Hugh Dickins 已提交
1504
			__count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scanned);
1505
	}
1506
	spin_unlock_irq(&zone->lru_lock);
1507

1508
	if (nr_taken == 0)
1509
		return 0;
A
Andy Whitcroft 已提交
1510

1511
	nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
1512 1513 1514
				&nr_dirty, &nr_unqueued_dirty, &nr_congested,
				&nr_writeback, &nr_immediate,
				false);
1515

1516 1517
	spin_lock_irq(&zone->lru_lock);

1518
	reclaim_stat->recent_scanned[file] += nr_taken;
1519

Y
Ying Han 已提交
1520 1521 1522 1523 1524 1525 1526 1527
	if (global_reclaim(sc)) {
		if (current_is_kswapd())
			__count_zone_vm_events(PGSTEAL_KSWAPD, zone,
					       nr_reclaimed);
		else
			__count_zone_vm_events(PGSTEAL_DIRECT, zone,
					       nr_reclaimed);
	}
N
Nick Piggin 已提交
1528

1529
	putback_inactive_pages(lruvec, &page_list);
1530

1531
	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1532 1533 1534 1535

	spin_unlock_irq(&zone->lru_lock);

	free_hot_cold_page_list(&page_list, 1);
1536

1537 1538 1539 1540 1541 1542 1543 1544 1545 1546
	/*
	 * 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.
	 *
1547 1548 1549
	 * Once a zone is flagged ZONE_WRITEBACK, kswapd will count the number
	 * of pages under pages flagged for immediate reclaim and stall if any
	 * are encountered in the nr_immediate check below.
1550
	 */
1551
	if (nr_writeback && nr_writeback == nr_taken)
1552
		zone_set_flag(zone, ZONE_WRITEBACK);
1553

1554
	/*
1555 1556
	 * memcg will stall in page writeback so only consider forcibly
	 * stalling for global reclaim
1557
	 */
1558
	if (global_reclaim(sc)) {
1559 1560 1561 1562 1563 1564 1565
		/*
		 * Tag a zone as congested if all the dirty pages scanned were
		 * backed by a congested BDI and wait_iff_congested will stall.
		 */
		if (nr_dirty && nr_dirty == nr_congested)
			zone_set_flag(zone, ZONE_CONGESTED);

1566 1567 1568 1569 1570 1571 1572 1573 1574 1575 1576 1577 1578 1579 1580 1581
		/*
		 * If dirty pages are scanned that are not queued for IO, it
		 * implies that flushers are not keeping up. In this case, flag
		 * the zone ZONE_TAIL_LRU_DIRTY and kswapd will start writing
		 * pages from reclaim context. It will forcibly stall in the
		 * next check.
		 */
		if (nr_unqueued_dirty == nr_taken)
			zone_set_flag(zone, ZONE_TAIL_LRU_DIRTY);

		/*
		 * In addition, 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.
		 */
1582 1583
		if ((nr_unqueued_dirty == nr_taken || nr_immediate) &&
		    current_may_throttle())
1584
			congestion_wait(BLK_RW_ASYNC, HZ/10);
1585
	}
1586

1587 1588 1589 1590 1591
	/*
	 * Stall direct reclaim for IO completions if underlying BDIs or zone
	 * is congested. Allow kswapd to continue until it starts encountering
	 * unqueued dirty pages or cycling through the LRU too quickly.
	 */
1592 1593
	if (!sc->hibernation_mode && !current_is_kswapd() &&
	    current_may_throttle())
1594 1595
		wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);

1596 1597 1598
	trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
		zone_idx(zone),
		nr_scanned, nr_reclaimed,
1599
		sc->priority,
M
Mel Gorman 已提交
1600
		trace_shrink_flags(file));
1601
	return nr_reclaimed;
L
Linus Torvalds 已提交
1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620
}

/*
 * This moves pages from the active list to the inactive list.
 *
 * We move them the other way if the page is referenced by one or more
 * processes, from rmap.
 *
 * If the pages are mostly unmapped, the processing is fast and it is
 * appropriate to hold zone->lru_lock across the whole operation.  But if
 * the pages are mapped, the processing is slow (page_referenced()) so we
 * should drop zone->lru_lock around each page.  It's impossible to balance
 * this, so instead we remove the pages from the LRU while processing them.
 * It is safe to rely on PG_active against the non-LRU pages in here because
 * nobody will play with that bit on a non-LRU page.
 *
 * The downside is that we have to touch page->_count against each page.
 * But we had to alter page->flags anyway.
 */
1621

1622
static void move_active_pages_to_lru(struct lruvec *lruvec,
1623
				     struct list_head *list,
1624
				     struct list_head *pages_to_free,
1625 1626
				     enum lru_list lru)
{
1627
	struct zone *zone = lruvec_zone(lruvec);
1628 1629
	unsigned long pgmoved = 0;
	struct page *page;
1630
	int nr_pages;
1631 1632 1633

	while (!list_empty(list)) {
		page = lru_to_page(list);
1634
		lruvec = mem_cgroup_page_lruvec(page, zone);
1635

1636
		VM_BUG_ON_PAGE(PageLRU(page), page);
1637 1638
		SetPageLRU(page);

1639 1640
		nr_pages = hpage_nr_pages(page);
		mem_cgroup_update_lru_size(lruvec, lru, nr_pages);
1641
		list_move(&page->lru, &lruvec->lists[lru]);
1642
		pgmoved += nr_pages;
1643

1644 1645 1646
		if (put_page_testzero(page)) {
			__ClearPageLRU(page);
			__ClearPageActive(page);
1647
			del_page_from_lru_list(page, lruvec, lru);
1648 1649 1650 1651 1652 1653 1654

			if (unlikely(PageCompound(page))) {
				spin_unlock_irq(&zone->lru_lock);
				(*get_compound_page_dtor(page))(page);
				spin_lock_irq(&zone->lru_lock);
			} else
				list_add(&page->lru, pages_to_free);
1655 1656 1657 1658 1659 1660
		}
	}
	__mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
	if (!is_active_lru(lru))
		__count_vm_events(PGDEACTIVATE, pgmoved);
}
1661

H
Hugh Dickins 已提交
1662
static void shrink_active_list(unsigned long nr_to_scan,
1663
			       struct lruvec *lruvec,
1664
			       struct scan_control *sc,
1665
			       enum lru_list lru)
L
Linus Torvalds 已提交
1666
{
1667
	unsigned long nr_taken;
H
Hugh Dickins 已提交
1668
	unsigned long nr_scanned;
1669
	unsigned long vm_flags;
L
Linus Torvalds 已提交
1670
	LIST_HEAD(l_hold);	/* The pages which were snipped off */
1671
	LIST_HEAD(l_active);
1672
	LIST_HEAD(l_inactive);
L
Linus Torvalds 已提交
1673
	struct page *page;
1674
	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1675
	unsigned long nr_rotated = 0;
1676
	isolate_mode_t isolate_mode = 0;
1677
	int file = is_file_lru(lru);
1678
	struct zone *zone = lruvec_zone(lruvec);
L
Linus Torvalds 已提交
1679 1680

	lru_add_drain();
1681 1682

	if (!sc->may_unmap)
1683
		isolate_mode |= ISOLATE_UNMAPPED;
1684
	if (!sc->may_writepage)
1685
		isolate_mode |= ISOLATE_CLEAN;
1686

L
Linus Torvalds 已提交
1687
	spin_lock_irq(&zone->lru_lock);
1688

1689 1690
	nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
				     &nr_scanned, sc, isolate_mode, lru);
1691
	if (global_reclaim(sc))
H
Hugh Dickins 已提交
1692
		zone->pages_scanned += nr_scanned;
1693

1694
	reclaim_stat->recent_scanned[file] += nr_taken;
1695

H
Hugh Dickins 已提交
1696
	__count_zone_vm_events(PGREFILL, zone, nr_scanned);
1697
	__mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
K
KOSAKI Motohiro 已提交
1698
	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
L
Linus Torvalds 已提交
1699 1700 1701 1702 1703 1704
	spin_unlock_irq(&zone->lru_lock);

	while (!list_empty(&l_hold)) {
		cond_resched();
		page = lru_to_page(&l_hold);
		list_del(&page->lru);
1705

1706
		if (unlikely(!page_evictable(page))) {
L
Lee Schermerhorn 已提交
1707 1708 1709 1710
			putback_lru_page(page);
			continue;
		}

1711 1712 1713 1714 1715 1716 1717 1718
		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);
			}
		}

1719 1720
		if (page_referenced(page, 0, sc->target_mem_cgroup,
				    &vm_flags)) {
1721
			nr_rotated += hpage_nr_pages(page);
1722 1723 1724 1725 1726 1727 1728 1729 1730
			/*
			 * 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.
			 */
1731
			if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1732 1733 1734 1735
				list_add(&page->lru, &l_active);
				continue;
			}
		}
1736

1737
		ClearPageActive(page);	/* we are de-activating */
L
Linus Torvalds 已提交
1738 1739 1740
		list_add(&page->lru, &l_inactive);
	}

1741
	/*
1742
	 * Move pages back to the lru list.
1743
	 */
1744
	spin_lock_irq(&zone->lru_lock);
1745
	/*
1746 1747 1748 1749
	 * Count referenced pages from currently used mappings as rotated,
	 * even though only some of them are actually re-activated.  This
	 * helps balance scan pressure between file and anonymous pages in
	 * get_scan_ratio.
1750
	 */
1751
	reclaim_stat->recent_rotated[file] += nr_rotated;
1752

1753 1754
	move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
	move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
K
KOSAKI Motohiro 已提交
1755
	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1756
	spin_unlock_irq(&zone->lru_lock);
1757 1758

	free_hot_cold_page_list(&l_hold, 1);
L
Linus Torvalds 已提交
1759 1760
}

1761
#ifdef CONFIG_SWAP
1762
static int inactive_anon_is_low_global(struct zone *zone)
1763 1764 1765 1766 1767 1768 1769 1770 1771 1772 1773 1774
{
	unsigned long active, inactive;

	active = zone_page_state(zone, NR_ACTIVE_ANON);
	inactive = zone_page_state(zone, NR_INACTIVE_ANON);

	if (inactive * zone->inactive_ratio < active)
		return 1;

	return 0;
}

1775 1776
/**
 * inactive_anon_is_low - check if anonymous pages need to be deactivated
1777
 * @lruvec: LRU vector to check
1778 1779 1780 1781
 *
 * Returns true if the zone does not have enough inactive anon pages,
 * meaning some active anon pages need to be deactivated.
 */
1782
static int inactive_anon_is_low(struct lruvec *lruvec)
1783
{
1784 1785 1786 1787 1788 1789 1790
	/*
	 * If we don't have swap space, anonymous page deactivation
	 * is pointless.
	 */
	if (!total_swap_pages)
		return 0;

1791
	if (!mem_cgroup_disabled())
1792
		return mem_cgroup_inactive_anon_is_low(lruvec);
1793

1794
	return inactive_anon_is_low_global(lruvec_zone(lruvec));
1795
}
1796
#else
1797
static inline int inactive_anon_is_low(struct lruvec *lruvec)
1798 1799 1800 1801
{
	return 0;
}
#endif
1802

1803 1804
/**
 * inactive_file_is_low - check if file pages need to be deactivated
1805
 * @lruvec: LRU vector to check
1806 1807 1808 1809 1810 1811 1812 1813 1814 1815 1816
 *
 * When the system is doing streaming IO, memory pressure here
 * ensures that active file pages get deactivated, until more
 * than half of the file pages are on the inactive list.
 *
 * Once we get to that situation, protect the system's working
 * set from being evicted by disabling active file page aging.
 *
 * This uses a different ratio than the anonymous pages, because
 * the page cache uses a use-once replacement algorithm.
 */
1817
static int inactive_file_is_low(struct lruvec *lruvec)
1818
{
1819 1820 1821 1822 1823
	unsigned long inactive;
	unsigned long active;

	inactive = get_lru_size(lruvec, LRU_INACTIVE_FILE);
	active = get_lru_size(lruvec, LRU_ACTIVE_FILE);
1824

1825
	return active > inactive;
1826 1827
}

H
Hugh Dickins 已提交
1828
static int inactive_list_is_low(struct lruvec *lruvec, enum lru_list lru)
1829
{
H
Hugh Dickins 已提交
1830
	if (is_file_lru(lru))
1831
		return inactive_file_is_low(lruvec);
1832
	else
1833
		return inactive_anon_is_low(lruvec);
1834 1835
}

1836
static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1837
				 struct lruvec *lruvec, struct scan_control *sc)
1838
{
1839
	if (is_active_lru(lru)) {
H
Hugh Dickins 已提交
1840
		if (inactive_list_is_low(lruvec, lru))
1841
			shrink_active_list(nr_to_scan, lruvec, sc, lru);
1842 1843 1844
		return 0;
	}

1845
	return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
1846 1847
}

1848
static int vmscan_swappiness(struct scan_control *sc)
1849
{
1850
	if (global_reclaim(sc))
1851
		return vm_swappiness;
1852
	return mem_cgroup_swappiness(sc->target_mem_cgroup);
1853 1854
}

1855 1856 1857 1858 1859 1860 1861
enum scan_balance {
	SCAN_EQUAL,
	SCAN_FRACT,
	SCAN_ANON,
	SCAN_FILE,
};

1862 1863 1864 1865 1866 1867
/*
 * 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
1868 1869
 * 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
1870
 */
1871
static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
1872
			   unsigned long *nr)
1873
{
1874 1875 1876 1877
	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
	u64 fraction[2];
	u64 denominator = 0;	/* gcc */
	struct zone *zone = lruvec_zone(lruvec);
1878
	unsigned long anon_prio, file_prio;
1879
	enum scan_balance scan_balance;
1880
	unsigned long anon, file;
1881
	bool force_scan = false;
1882
	unsigned long ap, fp;
H
Hugh Dickins 已提交
1883
	enum lru_list lru;
1884 1885
	bool some_scanned;
	int pass;
1886

1887 1888 1889 1890 1891 1892 1893 1894 1895 1896
	/*
	 * If the zone or memcg is small, nr[l] can be 0.  This
	 * results in no scanning on this priority and a potential
	 * priority drop.  Global direct reclaim can go to the next
	 * zone and tends to have no problems. Global kswapd is for
	 * zone balancing and it needs to scan a minimum amount. When
	 * reclaiming for a memcg, a priority drop can cause high
	 * latencies, so it's better to scan a minimum amount there as
	 * well.
	 */
1897
	if (current_is_kswapd() && !zone_reclaimable(zone))
1898
		force_scan = true;
1899
	if (!global_reclaim(sc))
1900
		force_scan = true;
1901 1902

	/* If we have no swap space, do not bother scanning anon pages. */
1903
	if (!sc->may_swap || (get_nr_swap_pages() <= 0)) {
1904
		scan_balance = SCAN_FILE;
1905 1906
		goto out;
	}
1907

1908 1909 1910 1911 1912 1913 1914 1915
	/*
	 * Global reclaim will swap to prevent OOM even with no
	 * swappiness, but memcg users want to use this knob to
	 * disable swapping for individual groups completely when
	 * using the memory controller's swap limit feature would be
	 * too expensive.
	 */
	if (!global_reclaim(sc) && !vmscan_swappiness(sc)) {
1916
		scan_balance = SCAN_FILE;
1917 1918 1919 1920 1921 1922 1923 1924 1925
		goto out;
	}

	/*
	 * Do not apply any pressure balancing cleverness when the
	 * system is close to OOM, scan both anon and file equally
	 * (unless the swappiness setting disagrees with swapping).
	 */
	if (!sc->priority && vmscan_swappiness(sc)) {
1926
		scan_balance = SCAN_EQUAL;
1927 1928 1929
		goto out;
	}

1930 1931 1932 1933
	anon  = get_lru_size(lruvec, LRU_ACTIVE_ANON) +
		get_lru_size(lruvec, LRU_INACTIVE_ANON);
	file  = get_lru_size(lruvec, LRU_ACTIVE_FILE) +
		get_lru_size(lruvec, LRU_INACTIVE_FILE);
1934

1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952
	/*
	 * Prevent the reclaimer from falling into the cache trap: as
	 * cache pages start out inactive, every cache fault will tip
	 * the scan balance towards the file LRU.  And as the file LRU
	 * shrinks, so does the window for rotation from references.
	 * This means we have a runaway feedback loop where a tiny
	 * thrashing file LRU becomes infinitely more attractive than
	 * anon pages.  Try to detect this based on file LRU size.
	 */
	if (global_reclaim(sc)) {
		unsigned long free = zone_page_state(zone, NR_FREE_PAGES);

		if (unlikely(file + free <= high_wmark_pages(zone))) {
			scan_balance = SCAN_ANON;
			goto out;
		}
	}

1953 1954 1955 1956 1957
	/*
	 * There is enough inactive page cache, do not reclaim
	 * anything from the anonymous working set right now.
	 */
	if (!inactive_file_is_low(lruvec)) {
1958
		scan_balance = SCAN_FILE;
1959 1960 1961
		goto out;
	}

1962 1963
	scan_balance = SCAN_FRACT;

1964 1965 1966 1967
	/*
	 * With swappiness at 100, anonymous and file have the same priority.
	 * This scanning priority is essentially the inverse of IO cost.
	 */
1968
	anon_prio = vmscan_swappiness(sc);
H
Hugh Dickins 已提交
1969
	file_prio = 200 - anon_prio;
1970

1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981
	/*
	 * 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]
	 */
1982
	spin_lock_irq(&zone->lru_lock);
1983 1984 1985
	if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
		reclaim_stat->recent_scanned[0] /= 2;
		reclaim_stat->recent_rotated[0] /= 2;
1986 1987
	}

1988 1989 1990
	if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
		reclaim_stat->recent_scanned[1] /= 2;
		reclaim_stat->recent_rotated[1] /= 2;
1991 1992 1993
	}

	/*
1994 1995 1996
	 * 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.
1997
	 */
1998
	ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
1999
	ap /= reclaim_stat->recent_rotated[0] + 1;
2000

2001
	fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
2002
	fp /= reclaim_stat->recent_rotated[1] + 1;
2003
	spin_unlock_irq(&zone->lru_lock);
2004

2005 2006 2007 2008
	fraction[0] = ap;
	fraction[1] = fp;
	denominator = ap + fp + 1;
out:
2009 2010 2011 2012 2013 2014 2015
	some_scanned = false;
	/* Only use force_scan on second pass. */
	for (pass = 0; !some_scanned && pass < 2; pass++) {
		for_each_evictable_lru(lru) {
			int file = is_file_lru(lru);
			unsigned long size;
			unsigned long scan;
2016

2017 2018
			size = get_lru_size(lruvec, lru);
			scan = size >> sc->priority;
2019

2020 2021
			if (!scan && pass && force_scan)
				scan = min(size, SWAP_CLUSTER_MAX);
2022

2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035 2036 2037 2038 2039 2040 2041 2042 2043 2044 2045
			switch (scan_balance) {
			case SCAN_EQUAL:
				/* Scan lists relative to size */
				break;
			case SCAN_FRACT:
				/*
				 * Scan types proportional to swappiness and
				 * their relative recent reclaim efficiency.
				 */
				scan = div64_u64(scan * fraction[file],
							denominator);
				break;
			case SCAN_FILE:
			case SCAN_ANON:
				/* Scan one type exclusively */
				if ((scan_balance == SCAN_FILE) != file)
					scan = 0;
				break;
			default:
				/* Look ma, no brain */
				BUG();
			}
			nr[lru] = scan;
2046
			/*
2047 2048
			 * Skip the second pass and don't force_scan,
			 * if we found something to scan.
2049
			 */
2050
			some_scanned |= !!scan;
2051
		}
2052
	}
2053
}
2054

2055 2056 2057 2058 2059 2060
/*
 * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
 */
static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
{
	unsigned long nr[NR_LRU_LISTS];
2061
	unsigned long targets[NR_LRU_LISTS];
2062 2063 2064 2065 2066
	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;
2067
	bool scan_adjusted = false;
2068 2069 2070

	get_scan_count(lruvec, sc, nr);

2071 2072 2073
	/* Record the original scan target for proportional adjustments later */
	memcpy(targets, nr, sizeof(nr));

2074 2075 2076
	blk_start_plug(&plug);
	while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
					nr[LRU_INACTIVE_FILE]) {
2077 2078 2079
		unsigned long nr_anon, nr_file, percentage;
		unsigned long nr_scanned;

2080 2081 2082 2083 2084 2085 2086 2087 2088
		for_each_evictable_lru(lru) {
			if (nr[lru]) {
				nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
				nr[lru] -= nr_to_scan;

				nr_reclaimed += shrink_list(lru, nr_to_scan,
							    lruvec, sc);
			}
		}
2089 2090 2091 2092

		if (nr_reclaimed < nr_to_reclaim || scan_adjusted)
			continue;

2093
		/*
2094 2095 2096 2097
		 * For global direct reclaim, reclaim only the number of pages
		 * requested. Less care is taken to scan proportionally as it
		 * is more important to minimise direct reclaim stall latency
		 * than it is to properly age the LRU lists.
2098
		 */
2099
		if (global_reclaim(sc) && !current_is_kswapd())
2100
			break;
2101 2102 2103 2104 2105 2106 2107 2108 2109 2110 2111 2112 2113 2114 2115 2116 2117 2118 2119 2120 2121 2122 2123 2124 2125 2126 2127 2128 2129 2130 2131 2132 2133 2134 2135 2136 2137 2138 2139 2140 2141 2142

		/*
		 * For kswapd and memcg, reclaim at least the number of pages
		 * requested. Ensure that the anon and file LRUs shrink
		 * 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];

		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;
2143 2144 2145 2146 2147 2148 2149 2150 2151 2152 2153 2154 2155 2156 2157
	}
	blk_finish_plug(&plug);
	sc->nr_reclaimed += nr_reclaimed;

	/*
	 * Even if we did not try to evict anon pages at all, we want to
	 * rebalance the anon lru active/inactive ratio.
	 */
	if (inactive_anon_is_low(lruvec))
		shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
				   sc, LRU_ACTIVE_ANON);

	throttle_vm_writeout(sc->gfp_mask);
}

M
Mel Gorman 已提交
2158
/* Use reclaim/compaction for costly allocs or under memory pressure */
2159
static bool in_reclaim_compaction(struct scan_control *sc)
M
Mel Gorman 已提交
2160
{
2161
	if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
M
Mel Gorman 已提交
2162
			(sc->order > PAGE_ALLOC_COSTLY_ORDER ||
2163
			 sc->priority < DEF_PRIORITY - 2))
M
Mel Gorman 已提交
2164 2165 2166 2167 2168
		return true;

	return false;
}

2169
/*
M
Mel Gorman 已提交
2170 2171 2172 2173 2174
 * 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.
2175
 */
2176
static inline bool should_continue_reclaim(struct zone *zone,
2177 2178 2179 2180 2181 2182 2183 2184
					unsigned long nr_reclaimed,
					unsigned long nr_scanned,
					struct scan_control *sc)
{
	unsigned long pages_for_compaction;
	unsigned long inactive_lru_pages;

	/* If not in reclaim/compaction mode, stop */
2185
	if (!in_reclaim_compaction(sc))
2186 2187
		return false;

2188 2189 2190 2191 2192 2193 2194 2195 2196 2197 2198 2199 2200 2201 2202 2203 2204 2205 2206 2207 2208 2209
	/* Consider stopping depending on scan and reclaim activity */
	if (sc->gfp_mask & __GFP_REPEAT) {
		/*
		 * For __GFP_REPEAT allocations, stop reclaiming if the
		 * full LRU list has been scanned and we are still failing
		 * to reclaim pages. This full LRU scan is potentially
		 * expensive but a __GFP_REPEAT caller really wants to succeed
		 */
		if (!nr_reclaimed && !nr_scanned)
			return false;
	} else {
		/*
		 * For non-__GFP_REPEAT allocations which can presumably
		 * fail without consequence, stop if we failed to reclaim
		 * any pages from the last SWAP_CLUSTER_MAX number of
		 * pages that were scanned. This will return to the
		 * caller faster at the risk reclaim/compaction and
		 * the resulting allocation attempt fails
		 */
		if (!nr_reclaimed)
			return false;
	}
2210 2211 2212 2213 2214 2215

	/*
	 * If we have not reclaimed enough pages for compaction and the
	 * inactive lists are large enough, continue reclaiming
	 */
	pages_for_compaction = (2UL << sc->order);
2216
	inactive_lru_pages = zone_page_state(zone, NR_INACTIVE_FILE);
2217
	if (get_nr_swap_pages() > 0)
2218
		inactive_lru_pages += zone_page_state(zone, NR_INACTIVE_ANON);
2219 2220 2221 2222 2223
	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 */
2224
	switch (compaction_suitable(zone, sc->order)) {
2225 2226 2227 2228 2229 2230 2231 2232
	case COMPACT_PARTIAL:
	case COMPACT_CONTINUE:
		return false;
	default:
		return true;
	}
}

2233
static void shrink_zone(struct zone *zone, struct scan_control *sc)
L
Linus Torvalds 已提交
2234
{
2235
	unsigned long nr_reclaimed, nr_scanned;
L
Linus Torvalds 已提交
2236

2237 2238 2239 2240 2241 2242
	do {
		struct mem_cgroup *root = sc->target_mem_cgroup;
		struct mem_cgroup_reclaim_cookie reclaim = {
			.zone = zone,
			.priority = sc->priority,
		};
2243
		struct mem_cgroup *memcg;
2244

2245 2246
		nr_reclaimed = sc->nr_reclaimed;
		nr_scanned = sc->nr_scanned;
L
Linus Torvalds 已提交
2247

2248 2249
		memcg = mem_cgroup_iter(root, NULL, &reclaim);
		do {
2250
			struct lruvec *lruvec;
2251

2252
			lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2253

2254
			shrink_lruvec(lruvec, sc);
2255

2256
			/*
2257 2258
			 * Direct reclaim and kswapd have to scan all memory
			 * cgroups to fulfill the overall scan target for the
2259
			 * zone.
2260 2261 2262 2263 2264
			 *
			 * 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.
2265
			 */
2266 2267
			if (!global_reclaim(sc) &&
					sc->nr_reclaimed >= sc->nr_to_reclaim) {
2268 2269 2270
				mem_cgroup_iter_break(root, memcg);
				break;
			}
2271 2272
			memcg = mem_cgroup_iter(root, memcg, &reclaim);
		} while (memcg);
2273 2274 2275 2276 2277

		vmpressure(sc->gfp_mask, sc->target_mem_cgroup,
			   sc->nr_scanned - nr_scanned,
			   sc->nr_reclaimed - nr_reclaimed);

2278 2279
	} while (should_continue_reclaim(zone, sc->nr_reclaimed - nr_reclaimed,
					 sc->nr_scanned - nr_scanned, sc));
2280 2281
}

2282 2283 2284 2285 2286 2287 2288 2289 2290 2291 2292 2293 2294 2295 2296 2297 2298
/* Returns true if compaction should go ahead for a high-order request */
static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
{
	unsigned long balance_gap, watermark;
	bool watermark_ok;

	/* Do not consider compaction for orders reclaim is meant to satisfy */
	if (sc->order <= PAGE_ALLOC_COSTLY_ORDER)
		return false;

	/*
	 * Compaction takes time to run and there are potentially other
	 * callers using the pages just freed. Continue reclaiming until
	 * there is a buffer of free pages available to give compaction
	 * a reasonable chance of completing and allocating the page
	 */
	balance_gap = min(low_wmark_pages(zone),
2299
		(zone->managed_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2300 2301 2302 2303 2304 2305 2306 2307
			KSWAPD_ZONE_BALANCE_GAP_RATIO);
	watermark = high_wmark_pages(zone) + balance_gap + (2UL << sc->order);
	watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0);

	/*
	 * If compaction is deferred, reclaim up to a point where
	 * compaction will have a chance of success when re-enabled
	 */
2308
	if (compaction_deferred(zone, sc->order))
2309 2310 2311 2312 2313 2314 2315 2316 2317
		return watermark_ok;

	/* If compaction is not ready to start, keep reclaiming */
	if (!compaction_suitable(zone, sc->order))
		return false;

	return watermark_ok;
}

L
Linus Torvalds 已提交
2318 2319 2320 2321 2322
/*
 * 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.
 *
2323 2324
 * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
 * Because:
L
Linus Torvalds 已提交
2325 2326
 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
 *    allocation or
2327 2328 2329
 * b) The target zone may be at high_wmark_pages(zone) but the lower zones
 *    must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
 *    zone defense algorithm.
L
Linus Torvalds 已提交
2330 2331 2332
 *
 * If a zone is deemed to be full of pinned pages then just give it a light
 * scan then give up on it.
2333 2334
 *
 * This function returns true if a zone is being reclaimed for a costly
2335
 * high-order allocation and compaction is ready to begin. This indicates to
2336 2337
 * the caller that it should consider retrying the allocation instead of
 * further reclaim.
L
Linus Torvalds 已提交
2338
 */
2339
static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
L
Linus Torvalds 已提交
2340
{
2341
	struct zoneref *z;
2342
	struct zone *zone;
2343 2344
	unsigned long nr_soft_reclaimed;
	unsigned long nr_soft_scanned;
2345
	unsigned long lru_pages = 0;
2346
	bool aborted_reclaim = false;
2347
	struct reclaim_state *reclaim_state = current->reclaim_state;
2348
	gfp_t orig_mask;
2349 2350 2351
	struct shrink_control shrink = {
		.gfp_mask = sc->gfp_mask,
	};
2352
	enum zone_type requested_highidx = gfp_zone(sc->gfp_mask);
2353

2354 2355 2356 2357 2358
	/*
	 * 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
	 */
2359
	orig_mask = sc->gfp_mask;
2360 2361 2362
	if (buffer_heads_over_limit)
		sc->gfp_mask |= __GFP_HIGHMEM;

2363
	nodes_clear(shrink.nodes_to_scan);
2364

2365 2366
	for_each_zone_zonelist_nodemask(zone, z, zonelist,
					gfp_zone(sc->gfp_mask), sc->nodemask) {
2367
		if (!populated_zone(zone))
L
Linus Torvalds 已提交
2368
			continue;
2369 2370 2371 2372
		/*
		 * Take care memory controller reclaiming has small influence
		 * to global LRU.
		 */
2373
		if (global_reclaim(sc)) {
2374 2375
			if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
				continue;
2376 2377

			lru_pages += zone_reclaimable_pages(zone);
2378
			node_set(zone_to_nid(zone), shrink.nodes_to_scan);
2379

2380 2381
			if (sc->priority != DEF_PRIORITY &&
			    !zone_reclaimable(zone))
2382
				continue;	/* Let kswapd poll it */
2383
			if (IS_ENABLED(CONFIG_COMPACTION)) {
2384
				/*
2385 2386 2387 2388 2389
				 * 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
2390 2391
				 * noticeable problem, like transparent huge
				 * page allocations.
2392
				 */
2393 2394
				if ((zonelist_zone_idx(z) <= requested_highidx)
				    && compaction_ready(zone, sc)) {
2395
					aborted_reclaim = true;
2396
					continue;
2397
				}
2398
			}
2399 2400 2401 2402 2403 2404 2405 2406 2407 2408 2409 2410
			/*
			 * This steals pages from memory cgroups over softlimit
			 * and returns the number of reclaimed pages and
			 * scanned pages. This works for global memory pressure
			 * and balancing, not for a memcg's limit.
			 */
			nr_soft_scanned = 0;
			nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
						sc->order, sc->gfp_mask,
						&nr_soft_scanned);
			sc->nr_reclaimed += nr_soft_reclaimed;
			sc->nr_scanned += nr_soft_scanned;
2411
			/* need some check for avoid more shrink_zone() */
2412
		}
2413

2414
		shrink_zone(zone, sc);
L
Linus Torvalds 已提交
2415
	}
2416

2417 2418 2419 2420 2421 2422 2423
	/*
	 * Don't shrink slabs when reclaiming memory from over limit cgroups
	 * but do shrink slab at least once when aborting reclaim for
	 * compaction to avoid unevenly scanning file/anon LRU pages over slab
	 * pages.
	 */
	if (global_reclaim(sc)) {
2424
		shrink_slab(&shrink, sc->nr_scanned, lru_pages);
2425 2426 2427 2428 2429 2430
		if (reclaim_state) {
			sc->nr_reclaimed += reclaim_state->reclaimed_slab;
			reclaim_state->reclaimed_slab = 0;
		}
	}

2431 2432 2433 2434 2435 2436
	/*
	 * Restore to original mask to avoid the impact on the caller if we
	 * promoted it to __GFP_HIGHMEM.
	 */
	sc->gfp_mask = orig_mask;

2437
	return aborted_reclaim;
2438 2439
}

2440
/* All zones in zonelist are unreclaimable? */
2441 2442 2443 2444 2445 2446 2447 2448 2449 2450 2451 2452
static bool all_unreclaimable(struct zonelist *zonelist,
		struct scan_control *sc)
{
	struct zoneref *z;
	struct zone *zone;

	for_each_zone_zonelist_nodemask(zone, z, zonelist,
			gfp_zone(sc->gfp_mask), sc->nodemask) {
		if (!populated_zone(zone))
			continue;
		if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
			continue;
2453
		if (zone_reclaimable(zone))
2454
			return false;
2455 2456
	}

2457
	return true;
L
Linus Torvalds 已提交
2458
}
2459

L
Linus Torvalds 已提交
2460 2461 2462 2463 2464 2465 2466 2467
/*
 * 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
2468 2469 2470 2471
 * 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.
2472 2473 2474
 *
 * returns:	0, if no pages reclaimed
 * 		else, the number of pages reclaimed
L
Linus Torvalds 已提交
2475
 */
2476
static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2477
					  struct scan_control *sc)
L
Linus Torvalds 已提交
2478
{
2479
	unsigned long total_scanned = 0;
2480
	unsigned long writeback_threshold;
2481
	bool aborted_reclaim;
L
Linus Torvalds 已提交
2482

2483 2484
	delayacct_freepages_start();

2485
	if (global_reclaim(sc))
2486
		count_vm_event(ALLOCSTALL);
L
Linus Torvalds 已提交
2487

2488
	do {
2489 2490
		vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
				sc->priority);
2491
		sc->nr_scanned = 0;
2492
		aborted_reclaim = shrink_zones(zonelist, sc);
2493

2494
		total_scanned += sc->nr_scanned;
2495
		if (sc->nr_reclaimed >= sc->nr_to_reclaim)
L
Linus Torvalds 已提交
2496 2497
			goto out;

2498 2499 2500 2501 2502 2503 2504
		/*
		 * If we're getting trouble reclaiming, start doing
		 * writepage even in laptop mode.
		 */
		if (sc->priority < DEF_PRIORITY - 2)
			sc->may_writepage = 1;

L
Linus Torvalds 已提交
2505 2506 2507 2508 2509 2510 2511
		/*
		 * Try to write back as many pages as we just scanned.  This
		 * tends to cause slow streaming writers to write data to the
		 * disk smoothly, at the dirtying rate, which is nice.   But
		 * that's undesirable in laptop mode, where we *want* lumpy
		 * writeout.  So in laptop mode, write out the whole world.
		 */
2512 2513
		writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
		if (total_scanned > writeback_threshold) {
2514 2515
			wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
						WB_REASON_TRY_TO_FREE_PAGES);
2516
			sc->may_writepage = 1;
L
Linus Torvalds 已提交
2517
		}
2518
	} while (--sc->priority >= 0 && !aborted_reclaim);
2519

L
Linus Torvalds 已提交
2520
out:
2521 2522
	delayacct_freepages_end();

2523 2524 2525
	if (sc->nr_reclaimed)
		return sc->nr_reclaimed;

2526 2527 2528 2529 2530 2531 2532 2533
	/*
	 * As hibernation is going on, kswapd is freezed so that it can't mark
	 * the zone into all_unreclaimable. Thus bypassing all_unreclaimable
	 * check.
	 */
	if (oom_killer_disabled)
		return 0;

2534 2535
	/* Aborted reclaim to try compaction? don't OOM, then */
	if (aborted_reclaim)
2536 2537
		return 1;

2538
	/* top priority shrink_zones still had more to do? don't OOM, then */
2539
	if (global_reclaim(sc) && !all_unreclaimable(zonelist, sc))
2540 2541 2542
		return 1;

	return 0;
L
Linus Torvalds 已提交
2543 2544
}

2545 2546 2547 2548 2549 2550 2551 2552 2553 2554
static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
{
	struct zone *zone;
	unsigned long pfmemalloc_reserve = 0;
	unsigned long free_pages = 0;
	int i;
	bool wmark_ok;

	for (i = 0; i <= ZONE_NORMAL; i++) {
		zone = &pgdat->node_zones[i];
2555 2556 2557
		if (!populated_zone(zone))
			continue;

2558 2559 2560 2561
		pfmemalloc_reserve += min_wmark_pages(zone);
		free_pages += zone_page_state(zone, NR_FREE_PAGES);
	}

2562 2563 2564 2565
	/* If there are no reserves (unexpected config) then do not throttle */
	if (!pfmemalloc_reserve)
		return true;

2566 2567 2568 2569 2570 2571 2572 2573 2574 2575 2576 2577 2578 2579 2580 2581
	wmark_ok = free_pages > pfmemalloc_reserve / 2;

	/* kswapd must be awake if processes are being throttled */
	if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
		pgdat->classzone_idx = min(pgdat->classzone_idx,
						(enum zone_type)ZONE_NORMAL);
		wake_up_interruptible(&pgdat->kswapd_wait);
	}

	return wmark_ok;
}

/*
 * Throttle direct reclaimers if backing storage is backed by the network
 * and the PFMEMALLOC reserve for the preferred node is getting dangerously
 * depleted. kswapd will continue to make progress and wake the processes
2582 2583 2584 2585
 * 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.
2586
 */
2587
static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
2588 2589
					nodemask_t *nodemask)
{
2590
	struct zoneref *z;
2591
	struct zone *zone;
2592
	pg_data_t *pgdat = NULL;
2593 2594 2595 2596 2597 2598 2599 2600 2601

	/*
	 * 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)
2602 2603 2604 2605 2606 2607 2608 2609
		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;
2610

2611 2612 2613 2614 2615 2616 2617 2618 2619 2620 2621 2622 2623 2624 2625 2626 2627 2628 2629 2630 2631 2632 2633 2634 2635 2636 2637 2638
	/*
	 * Check if the pfmemalloc reserves are ok by finding the first node
	 * with a usable ZONE_NORMAL or lower zone. The expectation is that
	 * GFP_KERNEL will be required for allocating network buffers when
	 * swapping over the network so ZONE_HIGHMEM is unusable.
	 *
	 * Throttling is based on the first usable node and throttled processes
	 * wait on a queue until kswapd makes progress and wakes them. There
	 * is an affinity then between processes waking up and where reclaim
	 * progress has been made assuming the process wakes on the same node.
	 * More importantly, processes running on remote nodes will not compete
	 * for remote pfmemalloc reserves and processes on different nodes
	 * should make reasonable progress.
	 */
	for_each_zone_zonelist_nodemask(zone, z, zonelist,
					gfp_mask, nodemask) {
		if (zone_idx(zone) > ZONE_NORMAL)
			continue;

		/* Throttle based on the first usable node */
		pgdat = zone->zone_pgdat;
		if (pfmemalloc_watermark_ok(pgdat))
			goto out;
		break;
	}

	/* If no zone was usable by the allocation flags then do not throttle */
	if (!pgdat)
2639
		goto out;
2640

2641 2642 2643
	/* Account for the throttling */
	count_vm_event(PGSCAN_DIRECT_THROTTLE);

2644 2645 2646 2647 2648 2649 2650 2651 2652 2653 2654
	/*
	 * If the caller cannot enter the filesystem, it's possible that it
	 * is due to the caller holding an FS lock or performing a journal
	 * transaction in the case of a filesystem like ext[3|4]. In this case,
	 * it is not safe to block on pfmemalloc_wait as kswapd could be
	 * blocked waiting on the same lock. Instead, throttle for up to a
	 * second before continuing.
	 */
	if (!(gfp_mask & __GFP_FS)) {
		wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
			pfmemalloc_watermark_ok(pgdat), HZ);
2655 2656

		goto check_pending;
2657 2658 2659 2660 2661
	}

	/* Throttle until kswapd wakes the process */
	wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
		pfmemalloc_watermark_ok(pgdat));
2662 2663 2664 2665 2666 2667 2668

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

out:
	return false;
2669 2670
}

2671
unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2672
				gfp_t gfp_mask, nodemask_t *nodemask)
2673
{
2674
	unsigned long nr_reclaimed;
2675
	struct scan_control sc = {
2676
		.gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
2677
		.may_writepage = !laptop_mode,
2678
		.nr_to_reclaim = SWAP_CLUSTER_MAX,
2679
		.may_unmap = 1,
2680
		.may_swap = 1,
2681
		.order = order,
2682
		.priority = DEF_PRIORITY,
2683
		.target_mem_cgroup = NULL,
2684
		.nodemask = nodemask,
2685 2686
	};

2687
	/*
2688 2689 2690
	 * 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.
2691
	 */
2692
	if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask))
2693 2694
		return 1;

2695 2696 2697 2698
	trace_mm_vmscan_direct_reclaim_begin(order,
				sc.may_writepage,
				gfp_mask);

2699
	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
2700 2701 2702 2703

	trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);

	return nr_reclaimed;
2704 2705
}

A
Andrew Morton 已提交
2706
#ifdef CONFIG_MEMCG
2707

2708
unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
2709
						gfp_t gfp_mask, bool noswap,
2710 2711
						struct zone *zone,
						unsigned long *nr_scanned)
2712 2713
{
	struct scan_control sc = {
2714
		.nr_scanned = 0,
2715
		.nr_to_reclaim = SWAP_CLUSTER_MAX,
2716 2717 2718 2719
		.may_writepage = !laptop_mode,
		.may_unmap = 1,
		.may_swap = !noswap,
		.order = 0,
2720
		.priority = 0,
2721
		.target_mem_cgroup = memcg,
2722
	};
2723
	struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2724

2725 2726
	sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
			(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2727

2728
	trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
2729 2730 2731
						      sc.may_writepage,
						      sc.gfp_mask);

2732 2733 2734 2735 2736 2737 2738
	/*
	 * NOTE: Although we can get the priority field, using it
	 * here is not a good idea, since it limits the pages we can scan.
	 * if we don't reclaim here, the shrink_zone from balance_pgdat
	 * will pick up pages from other mem cgroup's as well. We hack
	 * the priority and make it zero.
	 */
2739
	shrink_lruvec(lruvec, &sc);
2740 2741 2742

	trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);

2743
	*nr_scanned = sc.nr_scanned;
2744 2745 2746
	return sc.nr_reclaimed;
}

2747
unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
K
KOSAKI Motohiro 已提交
2748
					   gfp_t gfp_mask,
2749
					   bool noswap)
2750
{
2751
	struct zonelist *zonelist;
2752
	unsigned long nr_reclaimed;
2753
	int nid;
2754 2755
	struct scan_control sc = {
		.may_writepage = !laptop_mode,
2756
		.may_unmap = 1,
2757
		.may_swap = !noswap,
2758
		.nr_to_reclaim = SWAP_CLUSTER_MAX,
2759
		.order = 0,
2760
		.priority = DEF_PRIORITY,
2761
		.target_mem_cgroup = memcg,
2762
		.nodemask = NULL, /* we don't care the placement */
2763 2764 2765
		.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
				(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
	};
2766

2767 2768 2769 2770 2771
	/*
	 * 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.
	 */
2772
	nid = mem_cgroup_select_victim_node(memcg);
2773 2774

	zonelist = NODE_DATA(nid)->node_zonelists;
2775 2776 2777 2778 2779

	trace_mm_vmscan_memcg_reclaim_begin(0,
					    sc.may_writepage,
					    sc.gfp_mask);

2780
	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
2781 2782 2783 2784

	trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);

	return nr_reclaimed;
2785 2786 2787
}
#endif

2788
static void age_active_anon(struct zone *zone, struct scan_control *sc)
2789
{
2790
	struct mem_cgroup *memcg;
2791

2792 2793 2794 2795 2796
	if (!total_swap_pages)
		return;

	memcg = mem_cgroup_iter(NULL, NULL, NULL);
	do {
2797
		struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2798

2799
		if (inactive_anon_is_low(lruvec))
2800
			shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2801
					   sc, LRU_ACTIVE_ANON);
2802 2803 2804

		memcg = mem_cgroup_iter(NULL, memcg, NULL);
	} while (memcg);
2805 2806
}

2807 2808 2809 2810 2811 2812 2813
static bool zone_balanced(struct zone *zone, int order,
			  unsigned long balance_gap, int classzone_idx)
{
	if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone) +
				    balance_gap, classzone_idx, 0))
		return false;

2814 2815
	if (IS_ENABLED(CONFIG_COMPACTION) && order &&
	    !compaction_suitable(zone, order))
2816 2817 2818 2819 2820
		return false;

	return true;
}

2821
/*
2822 2823 2824 2825 2826 2827 2828 2829 2830 2831
 * pgdat_balanced() is used when checking if a node is balanced.
 *
 * For order-0, all zones must be balanced!
 *
 * For high-order allocations only zones that meet watermarks and are in a
 * zone allowed by the callers classzone_idx are added to balanced_pages. The
 * total of balanced pages must be at least 25% of the zones allowed by
 * classzone_idx for the node to be considered balanced. Forcing all zones to
 * be balanced for high orders can cause excessive reclaim when there are
 * imbalanced zones.
2832 2833 2834 2835
 * The choice of 25% is due to
 *   o a 16M DMA zone that is balanced will not balance a zone on any
 *     reasonable sized machine
 *   o On all other machines, the top zone must be at least a reasonable
L
Lucas De Marchi 已提交
2836
 *     percentage of the middle zones. For example, on 32-bit x86, highmem
2837 2838 2839 2840
 *     would need to be at least 256M for it to be balance a whole node.
 *     Similarly, on x86-64 the Normal zone would need to be at least 1G
 *     to balance a node on its own. These seemed like reasonable ratios.
 */
2841
static bool pgdat_balanced(pg_data_t *pgdat, int order, int classzone_idx)
2842
{
2843
	unsigned long managed_pages = 0;
2844
	unsigned long balanced_pages = 0;
2845 2846
	int i;

2847 2848 2849
	/* Check the watermark levels */
	for (i = 0; i <= classzone_idx; i++) {
		struct zone *zone = pgdat->node_zones + i;
2850

2851 2852 2853
		if (!populated_zone(zone))
			continue;

2854
		managed_pages += zone->managed_pages;
2855 2856 2857 2858 2859 2860 2861 2862

		/*
		 * A special case here:
		 *
		 * balance_pgdat() skips over all_unreclaimable after
		 * DEF_PRIORITY. Effectively, it considers them balanced so
		 * they must be considered balanced here as well!
		 */
2863
		if (!zone_reclaimable(zone)) {
2864
			balanced_pages += zone->managed_pages;
2865 2866 2867 2868
			continue;
		}

		if (zone_balanced(zone, order, 0, i))
2869
			balanced_pages += zone->managed_pages;
2870 2871 2872 2873 2874
		else if (!order)
			return false;
	}

	if (order)
2875
		return balanced_pages >= (managed_pages >> 2);
2876 2877
	else
		return true;
2878 2879
}

2880 2881 2882 2883 2884 2885 2886
/*
 * Prepare kswapd for sleeping. This verifies that there are no processes
 * waiting in throttle_direct_reclaim() and that watermarks have been met.
 *
 * Returns true if kswapd is ready to sleep
 */
static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
2887
					int classzone_idx)
2888 2889 2890
{
	/* If a direct reclaimer woke kswapd within HZ/10, it's premature */
	if (remaining)
2891 2892 2893 2894 2895 2896 2897 2898 2899 2900 2901 2902 2903 2904 2905
		return false;

	/*
	 * There is a potential race between when kswapd checks its watermarks
	 * and a process gets throttled. There is also a potential race if
	 * processes get throttled, kswapd wakes, a large process exits therby
	 * balancing the zones that causes kswapd to miss a wakeup. If kswapd
	 * is going to sleep, no process should be sleeping on pfmemalloc_wait
	 * so wake them now if necessary. If necessary, processes will wake
	 * kswapd and get throttled again
	 */
	if (waitqueue_active(&pgdat->pfmemalloc_wait)) {
		wake_up(&pgdat->pfmemalloc_wait);
		return false;
	}
2906

2907
	return pgdat_balanced(pgdat, order, classzone_idx);
2908 2909
}

2910 2911 2912
/*
 * kswapd shrinks the zone by the number of pages required to reach
 * the high watermark.
2913 2914
 *
 * Returns true if kswapd scanned at least the requested number of pages to
2915 2916
 * 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.
2917
 */
2918
static bool kswapd_shrink_zone(struct zone *zone,
2919
			       int classzone_idx,
2920
			       struct scan_control *sc,
2921 2922
			       unsigned long lru_pages,
			       unsigned long *nr_attempted)
2923
{
2924 2925
	int testorder = sc->order;
	unsigned long balance_gap;
2926 2927 2928 2929
	struct reclaim_state *reclaim_state = current->reclaim_state;
	struct shrink_control shrink = {
		.gfp_mask = sc->gfp_mask,
	};
2930
	bool lowmem_pressure;
2931 2932 2933

	/* Reclaim above the high watermark. */
	sc->nr_to_reclaim = max(SWAP_CLUSTER_MAX, high_wmark_pages(zone));
2934 2935 2936 2937 2938 2939 2940 2941 2942 2943 2944 2945 2946 2947 2948 2949 2950 2951 2952 2953 2954 2955 2956 2957 2958 2959 2960 2961 2962 2963 2964

	/*
	 * Kswapd reclaims only single pages with compaction enabled. Trying
	 * too hard to reclaim until contiguous free pages have become
	 * available can hurt performance by evicting too much useful data
	 * from memory. Do not reclaim more than needed for compaction.
	 */
	if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
			compaction_suitable(zone, sc->order) !=
				COMPACT_SKIPPED)
		testorder = 0;

	/*
	 * We put equal pressure on every zone, unless one zone has way too
	 * many pages free already. The "too many pages" is defined as the
	 * high wmark plus a "gap" where the gap is either the low
	 * watermark or 1% of the zone, whichever is smaller.
	 */
	balance_gap = min(low_wmark_pages(zone),
		(zone->managed_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
		KSWAPD_ZONE_BALANCE_GAP_RATIO);

	/*
	 * If there is no low memory pressure or the zone is balanced then no
	 * reclaim is necessary
	 */
	lowmem_pressure = (buffer_heads_over_limit && is_highmem(zone));
	if (!lowmem_pressure && zone_balanced(zone, testorder,
						balance_gap, classzone_idx))
		return true;

2965
	shrink_zone(zone, sc);
D
Dave Chinner 已提交
2966 2967
	nodes_clear(shrink.nodes_to_scan);
	node_set(zone_to_nid(zone), shrink.nodes_to_scan);
2968 2969

	reclaim_state->reclaimed_slab = 0;
2970
	shrink_slab(&shrink, sc->nr_scanned, lru_pages);
2971 2972
	sc->nr_reclaimed += reclaim_state->reclaimed_slab;

2973 2974 2975
	/* Account for the number of pages attempted to reclaim */
	*nr_attempted += sc->nr_to_reclaim;

2976 2977
	zone_clear_flag(zone, ZONE_WRITEBACK);

2978 2979 2980 2981 2982 2983
	/*
	 * If a zone reaches its high watermark, consider it to be no longer
	 * congested. It's possible there are dirty pages backed by congested
	 * BDIs but as pressure is relieved, speculatively avoid congestion
	 * waits.
	 */
2984
	if (zone_reclaimable(zone) &&
2985 2986 2987 2988 2989
	    zone_balanced(zone, testorder, 0, classzone_idx)) {
		zone_clear_flag(zone, ZONE_CONGESTED);
		zone_clear_flag(zone, ZONE_TAIL_LRU_DIRTY);
	}

2990
	return sc->nr_scanned >= sc->nr_to_reclaim;
2991 2992
}

L
Linus Torvalds 已提交
2993 2994
/*
 * For kswapd, balance_pgdat() will work across all this node's zones until
2995
 * they are all at high_wmark_pages(zone).
L
Linus Torvalds 已提交
2996
 *
2997
 * Returns the final order kswapd was reclaiming at
L
Linus Torvalds 已提交
2998 2999 3000 3001 3002 3003 3004 3005 3006 3007
 *
 * There is special handling here for zones which are full of pinned pages.
 * This can happen if the pages are all mlocked, or if they are all used by
 * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
 * What we do is to detect the case where all pages in the zone have been
 * scanned twice and there has been zero successful reclaim.  Mark the zone as
 * dead and from now on, only perform a short scan.  Basically we're polling
 * the zone for when the problem goes away.
 *
 * kswapd scans the zones in the highmem->normal->dma direction.  It skips
3008 3009 3010 3011 3012
 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
 * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
 * lower zones regardless of the number of free pages in the lower zones. This
 * interoperates with the page allocator fallback scheme to ensure that aging
 * of pages is balanced across the zones.
L
Linus Torvalds 已提交
3013
 */
3014
static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
3015
							int *classzone_idx)
L
Linus Torvalds 已提交
3016 3017
{
	int i;
3018
	int end_zone = 0;	/* Inclusive.  0 = ZONE_DMA */
3019 3020
	unsigned long nr_soft_reclaimed;
	unsigned long nr_soft_scanned;
3021 3022
	struct scan_control sc = {
		.gfp_mask = GFP_KERNEL,
3023
		.priority = DEF_PRIORITY,
3024
		.may_unmap = 1,
3025
		.may_swap = 1,
3026
		.may_writepage = !laptop_mode,
A
Andy Whitcroft 已提交
3027
		.order = order,
3028
		.target_mem_cgroup = NULL,
3029
	};
3030
	count_vm_event(PAGEOUTRUN);
L
Linus Torvalds 已提交
3031

3032
	do {
L
Linus Torvalds 已提交
3033
		unsigned long lru_pages = 0;
3034
		unsigned long nr_attempted = 0;
3035
		bool raise_priority = true;
3036
		bool pgdat_needs_compaction = (order > 0);
3037 3038

		sc.nr_reclaimed = 0;
L
Linus Torvalds 已提交
3039

3040 3041 3042 3043 3044 3045
		/*
		 * Scan in the highmem->dma direction for the highest
		 * zone which needs scanning
		 */
		for (i = pgdat->nr_zones - 1; i >= 0; i--) {
			struct zone *zone = pgdat->node_zones + i;
L
Linus Torvalds 已提交
3046

3047 3048
			if (!populated_zone(zone))
				continue;
L
Linus Torvalds 已提交
3049

3050 3051
			if (sc.priority != DEF_PRIORITY &&
			    !zone_reclaimable(zone))
3052
				continue;
L
Linus Torvalds 已提交
3053

3054 3055 3056 3057
			/*
			 * Do some background aging of the anon list, to give
			 * pages a chance to be referenced before reclaiming.
			 */
3058
			age_active_anon(zone, &sc);
3059

3060 3061 3062 3063 3064 3065 3066 3067 3068 3069 3070
			/*
			 * If the number of buffer_heads in the machine
			 * exceeds the maximum allowed level and this node
			 * has a highmem zone, force kswapd to reclaim from
			 * it to relieve lowmem pressure.
			 */
			if (buffer_heads_over_limit && is_highmem_idx(i)) {
				end_zone = i;
				break;
			}

3071
			if (!zone_balanced(zone, order, 0, 0)) {
3072
				end_zone = i;
A
Andrew Morton 已提交
3073
				break;
3074
			} else {
3075 3076 3077 3078
				/*
				 * If balanced, clear the dirty and congested
				 * flags
				 */
3079
				zone_clear_flag(zone, ZONE_CONGESTED);
3080
				zone_clear_flag(zone, ZONE_TAIL_LRU_DIRTY);
L
Linus Torvalds 已提交
3081 3082
			}
		}
3083

3084
		if (i < 0)
A
Andrew Morton 已提交
3085 3086
			goto out;

L
Linus Torvalds 已提交
3087 3088 3089
		for (i = 0; i <= end_zone; i++) {
			struct zone *zone = pgdat->node_zones + i;

3090 3091 3092
			if (!populated_zone(zone))
				continue;

3093
			lru_pages += zone_reclaimable_pages(zone);
3094 3095 3096 3097 3098 3099 3100 3101 3102 3103 3104

			/*
			 * If any zone is currently balanced then kswapd will
			 * not call compaction as it is expected that the
			 * necessary pages are already available.
			 */
			if (pgdat_needs_compaction &&
					zone_watermark_ok(zone, order,
						low_wmark_pages(zone),
						*classzone_idx, 0))
				pgdat_needs_compaction = false;
L
Linus Torvalds 已提交
3105 3106
		}

3107 3108 3109 3110 3111 3112 3113
		/*
		 * If we're getting trouble reclaiming, start doing writepage
		 * even in laptop mode.
		 */
		if (sc.priority < DEF_PRIORITY - 2)
			sc.may_writepage = 1;

L
Linus Torvalds 已提交
3114 3115 3116 3117 3118 3119 3120 3121 3122 3123 3124 3125
		/*
		 * Now scan the zone in the dma->highmem direction, stopping
		 * at the last zone which needs scanning.
		 *
		 * We do this because the page allocator works in the opposite
		 * direction.  This prevents the page allocator from allocating
		 * pages behind kswapd's direction of progress, which would
		 * cause too much scanning of the lower zones.
		 */
		for (i = 0; i <= end_zone; i++) {
			struct zone *zone = pgdat->node_zones + i;

3126
			if (!populated_zone(zone))
L
Linus Torvalds 已提交
3127 3128
				continue;

3129 3130
			if (sc.priority != DEF_PRIORITY &&
			    !zone_reclaimable(zone))
L
Linus Torvalds 已提交
3131 3132 3133
				continue;

			sc.nr_scanned = 0;
3134

3135 3136 3137 3138 3139 3140 3141 3142 3143
			nr_soft_scanned = 0;
			/*
			 * Call soft limit reclaim before calling shrink_zone.
			 */
			nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
							order, sc.gfp_mask,
							&nr_soft_scanned);
			sc.nr_reclaimed += nr_soft_reclaimed;

3144
			/*
3145 3146 3147 3148
			 * 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.
3149
			 */
3150 3151 3152
			if (kswapd_shrink_zone(zone, end_zone, &sc,
					lru_pages, &nr_attempted))
				raise_priority = false;
L
Linus Torvalds 已提交
3153
		}
3154 3155 3156 3157 3158 3159 3160 3161 3162 3163

		/*
		 * If the low watermark is met there is no need for processes
		 * to be throttled on pfmemalloc_wait as they should not be
		 * able to safely make forward progress. Wake them
		 */
		if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
				pfmemalloc_watermark_ok(pgdat))
			wake_up(&pgdat->pfmemalloc_wait);

L
Linus Torvalds 已提交
3164
		/*
3165 3166 3167 3168 3169 3170
		 * Fragmentation may mean that the system cannot be rebalanced
		 * for high-order allocations in all zones. If twice the
		 * allocation size has been reclaimed and the zones are still
		 * not balanced then recheck the watermarks at order-0 to
		 * prevent kswapd reclaiming excessively. Assume that a
		 * process requested a high-order can direct reclaim/compact.
L
Linus Torvalds 已提交
3171
		 */
3172 3173
		if (order && sc.nr_reclaimed >= 2UL << order)
			order = sc.order = 0;
3174

3175 3176 3177
		/* Check if kswapd should be suspending */
		if (try_to_freeze() || kthread_should_stop())
			break;
3178

3179 3180 3181 3182 3183 3184 3185
		/*
		 * Compact if necessary and kswapd is reclaiming at least the
		 * high watermark number of pages as requsted
		 */
		if (pgdat_needs_compaction && sc.nr_reclaimed > nr_attempted)
			compact_pgdat(pgdat, order);

3186
		/*
3187 3188
		 * Raise priority if scanning rate is too low or there was no
		 * progress in reclaiming pages
3189
		 */
3190 3191
		if (raise_priority || !sc.nr_reclaimed)
			sc.priority--;
3192
	} while (sc.priority >= 1 &&
3193
		 !pgdat_balanced(pgdat, order, *classzone_idx));
L
Linus Torvalds 已提交
3194

3195
out:
3196
	/*
3197
	 * Return the order we were reclaiming at so prepare_kswapd_sleep()
3198 3199 3200 3201
	 * makes a decision on the order we were last reclaiming at. However,
	 * if another caller entered the allocator slow path while kswapd
	 * was awake, order will remain at the higher level
	 */
3202
	*classzone_idx = end_zone;
3203
	return order;
L
Linus Torvalds 已提交
3204 3205
}

3206
static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
3207 3208 3209 3210 3211 3212 3213 3214 3215 3216
{
	long remaining = 0;
	DEFINE_WAIT(wait);

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

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

	/* Try to sleep for a short interval */
3217
	if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
3218 3219 3220 3221 3222 3223 3224 3225 3226
		remaining = schedule_timeout(HZ/10);
		finish_wait(&pgdat->kswapd_wait, &wait);
		prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
	}

	/*
	 * After a short sleep, check if it was a premature sleep. If not, then
	 * go fully to sleep until explicitly woken up.
	 */
3227
	if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
3228 3229 3230 3231 3232 3233 3234 3235 3236 3237 3238
		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);
3239

3240 3241 3242 3243 3244 3245 3246 3247
		/*
		 * 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);

3248 3249 3250
		if (!kthread_should_stop())
			schedule();

3251 3252 3253 3254 3255 3256 3257 3258 3259 3260
		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
3261 3262
/*
 * The background pageout daemon, started as a kernel thread
3263
 * from the init process.
L
Linus Torvalds 已提交
3264 3265 3266 3267 3268 3269 3270 3271 3272 3273 3274 3275
 *
 * 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)
{
3276
	unsigned long order, new_order;
3277
	unsigned balanced_order;
3278
	int classzone_idx, new_classzone_idx;
3279
	int balanced_classzone_idx;
L
Linus Torvalds 已提交
3280 3281
	pg_data_t *pgdat = (pg_data_t*)p;
	struct task_struct *tsk = current;
3282

L
Linus Torvalds 已提交
3283 3284 3285
	struct reclaim_state reclaim_state = {
		.reclaimed_slab = 0,
	};
3286
	const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
L
Linus Torvalds 已提交
3287

3288 3289
	lockdep_set_current_reclaim_state(GFP_KERNEL);

R
Rusty Russell 已提交
3290
	if (!cpumask_empty(cpumask))
3291
		set_cpus_allowed_ptr(tsk, cpumask);
L
Linus Torvalds 已提交
3292 3293 3294 3295 3296 3297 3298 3299 3300 3301 3302 3303 3304 3305
	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).
	 */
3306
	tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
3307
	set_freezable();
L
Linus Torvalds 已提交
3308

3309
	order = new_order = 0;
3310
	balanced_order = 0;
3311
	classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
3312
	balanced_classzone_idx = classzone_idx;
L
Linus Torvalds 已提交
3313
	for ( ; ; ) {
3314
		bool ret;
3315

3316 3317 3318 3319 3320
		/*
		 * If the last balance_pgdat was unsuccessful it's unlikely a
		 * new request of a similar or harder type will succeed soon
		 * so consider going to sleep on the basis we reclaimed at
		 */
3321 3322
		if (balanced_classzone_idx >= new_classzone_idx &&
					balanced_order == new_order) {
3323 3324 3325 3326 3327 3328
			new_order = pgdat->kswapd_max_order;
			new_classzone_idx = pgdat->classzone_idx;
			pgdat->kswapd_max_order =  0;
			pgdat->classzone_idx = pgdat->nr_zones - 1;
		}

3329
		if (order < new_order || classzone_idx > new_classzone_idx) {
L
Linus Torvalds 已提交
3330 3331
			/*
			 * Don't sleep if someone wants a larger 'order'
3332
			 * allocation or has tigher zone constraints
L
Linus Torvalds 已提交
3333 3334
			 */
			order = new_order;
3335
			classzone_idx = new_classzone_idx;
L
Linus Torvalds 已提交
3336
		} else {
3337 3338
			kswapd_try_to_sleep(pgdat, balanced_order,
						balanced_classzone_idx);
L
Linus Torvalds 已提交
3339
			order = pgdat->kswapd_max_order;
3340
			classzone_idx = pgdat->classzone_idx;
3341 3342
			new_order = order;
			new_classzone_idx = classzone_idx;
3343
			pgdat->kswapd_max_order = 0;
3344
			pgdat->classzone_idx = pgdat->nr_zones - 1;
L
Linus Torvalds 已提交
3345 3346
		}

3347 3348 3349 3350 3351 3352 3353 3354
		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
		 */
3355 3356
		if (!ret) {
			trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
3357 3358 3359
			balanced_classzone_idx = classzone_idx;
			balanced_order = balance_pgdat(pgdat, order,
						&balanced_classzone_idx);
3360
		}
L
Linus Torvalds 已提交
3361
	}
3362 3363

	current->reclaim_state = NULL;
L
Linus Torvalds 已提交
3364 3365 3366 3367 3368 3369
	return 0;
}

/*
 * A zone is low on free memory, so wake its kswapd task to service it.
 */
3370
void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
L
Linus Torvalds 已提交
3371 3372 3373
{
	pg_data_t *pgdat;

3374
	if (!populated_zone(zone))
L
Linus Torvalds 已提交
3375 3376
		return;

3377
	if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
L
Linus Torvalds 已提交
3378
		return;
3379
	pgdat = zone->zone_pgdat;
3380
	if (pgdat->kswapd_max_order < order) {
L
Linus Torvalds 已提交
3381
		pgdat->kswapd_max_order = order;
3382 3383
		pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
	}
3384
	if (!waitqueue_active(&pgdat->kswapd_wait))
L
Linus Torvalds 已提交
3385
		return;
3386
	if (zone_balanced(zone, order, 0, 0))
3387 3388 3389
		return;

	trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
3390
	wake_up_interruptible(&pgdat->kswapd_wait);
L
Linus Torvalds 已提交
3391 3392
}

3393
#ifdef CONFIG_HIBERNATION
L
Linus Torvalds 已提交
3394
/*
3395
 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
3396 3397 3398 3399 3400
 * 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
3401
 */
3402
unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
L
Linus Torvalds 已提交
3403
{
3404 3405
	struct reclaim_state reclaim_state;
	struct scan_control sc = {
3406 3407 3408
		.gfp_mask = GFP_HIGHUSER_MOVABLE,
		.may_swap = 1,
		.may_unmap = 1,
3409
		.may_writepage = 1,
3410 3411 3412
		.nr_to_reclaim = nr_to_reclaim,
		.hibernation_mode = 1,
		.order = 0,
3413
		.priority = DEF_PRIORITY,
L
Linus Torvalds 已提交
3414
	};
3415
	struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3416 3417
	struct task_struct *p = current;
	unsigned long nr_reclaimed;
L
Linus Torvalds 已提交
3418

3419 3420 3421 3422
	p->flags |= PF_MEMALLOC;
	lockdep_set_current_reclaim_state(sc.gfp_mask);
	reclaim_state.reclaimed_slab = 0;
	p->reclaim_state = &reclaim_state;
3423

3424
	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3425

3426 3427 3428
	p->reclaim_state = NULL;
	lockdep_clear_current_reclaim_state();
	p->flags &= ~PF_MEMALLOC;
3429

3430
	return nr_reclaimed;
L
Linus Torvalds 已提交
3431
}
3432
#endif /* CONFIG_HIBERNATION */
L
Linus Torvalds 已提交
3433 3434 3435 3436 3437

/* 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. */
3438 3439
static int cpu_callback(struct notifier_block *nfb, unsigned long action,
			void *hcpu)
L
Linus Torvalds 已提交
3440
{
3441
	int nid;
L
Linus Torvalds 已提交
3442

3443
	if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
3444
		for_each_node_state(nid, N_MEMORY) {
3445
			pg_data_t *pgdat = NODE_DATA(nid);
3446 3447 3448
			const struct cpumask *mask;

			mask = cpumask_of_node(pgdat->node_id);
3449

3450
			if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
L
Linus Torvalds 已提交
3451
				/* One of our CPUs online: restore mask */
3452
				set_cpus_allowed_ptr(pgdat->kswapd, mask);
L
Linus Torvalds 已提交
3453 3454 3455 3456 3457
		}
	}
	return NOTIFY_OK;
}

3458 3459 3460 3461 3462 3463 3464 3465 3466 3467 3468 3469 3470 3471 3472 3473
/*
 * This kswapd start function will be called by init and node-hot-add.
 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
 */
int kswapd_run(int nid)
{
	pg_data_t *pgdat = NODE_DATA(nid);
	int ret = 0;

	if (pgdat->kswapd)
		return 0;

	pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
	if (IS_ERR(pgdat->kswapd)) {
		/* failure at boot is fatal */
		BUG_ON(system_state == SYSTEM_BOOTING);
3474 3475
		pr_err("Failed to start kswapd on node %d\n", nid);
		ret = PTR_ERR(pgdat->kswapd);
3476
		pgdat->kswapd = NULL;
3477 3478 3479 3480
	}
	return ret;
}

3481
/*
3482
 * Called by memory hotplug when all memory in a node is offlined.  Caller must
3483
 * hold mem_hotplug_begin/end().
3484 3485 3486 3487 3488
 */
void kswapd_stop(int nid)
{
	struct task_struct *kswapd = NODE_DATA(nid)->kswapd;

3489
	if (kswapd) {
3490
		kthread_stop(kswapd);
3491 3492
		NODE_DATA(nid)->kswapd = NULL;
	}
3493 3494
}

L
Linus Torvalds 已提交
3495 3496
static int __init kswapd_init(void)
{
3497
	int nid;
3498

L
Linus Torvalds 已提交
3499
	swap_setup();
3500
	for_each_node_state(nid, N_MEMORY)
3501
 		kswapd_run(nid);
L
Linus Torvalds 已提交
3502 3503 3504 3505 3506
	hotcpu_notifier(cpu_callback, 0);
	return 0;
}

module_init(kswapd_init)
3507 3508 3509 3510 3511 3512 3513 3514 3515 3516

#ifdef CONFIG_NUMA
/*
 * Zone reclaim mode
 *
 * If non-zero call zone_reclaim when the number of free pages falls below
 * the watermarks.
 */
int zone_reclaim_mode __read_mostly;

3517
#define RECLAIM_OFF 0
3518
#define RECLAIM_ZONE (1<<0)	/* Run shrink_inactive_list on the zone */
3519 3520 3521
#define RECLAIM_WRITE (1<<1)	/* Writeout pages during reclaim */
#define RECLAIM_SWAP (1<<2)	/* Swap pages out during reclaim */

3522 3523 3524 3525 3526 3527 3528
/*
 * Priority for ZONE_RECLAIM. This determines the fraction of pages
 * of a node considered for each zone_reclaim. 4 scans 1/16th of
 * a zone.
 */
#define ZONE_RECLAIM_PRIORITY 4

3529 3530 3531 3532 3533 3534
/*
 * Percentage of pages in a zone that must be unmapped for zone_reclaim to
 * occur.
 */
int sysctl_min_unmapped_ratio = 1;

3535 3536 3537 3538 3539 3540
/*
 * 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;

3541 3542 3543 3544 3545 3546 3547 3548 3549 3550 3551 3552 3553 3554 3555 3556 3557 3558 3559 3560 3561 3562 3563 3564 3565 3566 3567 3568 3569 3570 3571 3572 3573 3574 3575 3576 3577 3578 3579 3580 3581 3582
static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
{
	unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
	unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
		zone_page_state(zone, NR_ACTIVE_FILE);

	/*
	 * It's possible for there to be more file mapped pages than
	 * accounted for by the pages on the file LRU lists because
	 * tmpfs pages accounted for as ANON can also be FILE_MAPPED
	 */
	return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
}

/* Work out how many page cache pages we can reclaim in this reclaim_mode */
static long zone_pagecache_reclaimable(struct zone *zone)
{
	long nr_pagecache_reclaimable;
	long delta = 0;

	/*
	 * If RECLAIM_SWAP is set, then all file pages are considered
	 * potentially reclaimable. Otherwise, we have to worry about
	 * pages like swapcache and zone_unmapped_file_pages() provides
	 * a better estimate
	 */
	if (zone_reclaim_mode & RECLAIM_SWAP)
		nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
	else
		nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);

	/* If we can't clean pages, remove dirty pages from consideration */
	if (!(zone_reclaim_mode & RECLAIM_WRITE))
		delta += zone_page_state(zone, NR_FILE_DIRTY);

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

	return nr_pagecache_reclaimable - delta;
}

3583 3584 3585
/*
 * Try to free up some pages from this zone through reclaim.
 */
3586
static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3587
{
3588
	/* Minimum pages needed in order to stay on node */
3589
	const unsigned long nr_pages = 1 << order;
3590 3591
	struct task_struct *p = current;
	struct reclaim_state reclaim_state;
3592 3593
	struct scan_control sc = {
		.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
3594
		.may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
3595
		.may_swap = 1,
3596
		.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3597
		.gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
3598
		.order = order,
3599
		.priority = ZONE_RECLAIM_PRIORITY,
3600
	};
3601 3602 3603
	struct shrink_control shrink = {
		.gfp_mask = sc.gfp_mask,
	};
3604
	unsigned long nr_slab_pages0, nr_slab_pages1;
3605 3606

	cond_resched();
3607 3608 3609 3610 3611 3612
	/*
	 * We need to be able to allocate from the reserves for RECLAIM_SWAP
	 * and we also need to be able to write out pages for RECLAIM_WRITE
	 * and RECLAIM_SWAP.
	 */
	p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
3613
	lockdep_set_current_reclaim_state(gfp_mask);
3614 3615
	reclaim_state.reclaimed_slab = 0;
	p->reclaim_state = &reclaim_state;
3616

3617
	if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
3618 3619 3620 3621 3622
		/*
		 * Free memory by calling shrink zone with increasing
		 * priorities until we have enough memory freed.
		 */
		do {
3623 3624
			shrink_zone(zone, &sc);
		} while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
3625
	}
3626

3627 3628
	nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
	if (nr_slab_pages0 > zone->min_slab_pages) {
3629
		/*
3630
		 * shrink_slab() does not currently allow us to determine how
3631 3632 3633 3634
		 * many pages were freed in this zone. So we take the current
		 * number of slab pages and shake the slab until it is reduced
		 * by the same nr_pages that we used for reclaiming unmapped
		 * pages.
3635
		 */
D
Dave Chinner 已提交
3636 3637
		nodes_clear(shrink.nodes_to_scan);
		node_set(zone_to_nid(zone), shrink.nodes_to_scan);
3638 3639 3640 3641
		for (;;) {
			unsigned long lru_pages = zone_reclaimable_pages(zone);

			/* No reclaimable slab or very low memory pressure */
3642
			if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages))
3643 3644 3645 3646 3647 3648 3649 3650
				break;

			/* Freed enough memory */
			nr_slab_pages1 = zone_page_state(zone,
							NR_SLAB_RECLAIMABLE);
			if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
				break;
		}
3651 3652 3653 3654 3655

		/*
		 * Update nr_reclaimed by the number of slab pages we
		 * reclaimed from this zone.
		 */
3656 3657 3658
		nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
		if (nr_slab_pages1 < nr_slab_pages0)
			sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1;
3659 3660
	}

3661
	p->reclaim_state = NULL;
3662
	current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
3663
	lockdep_clear_current_reclaim_state();
3664
	return sc.nr_reclaimed >= nr_pages;
3665
}
3666 3667 3668 3669

int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
{
	int node_id;
3670
	int ret;
3671 3672

	/*
3673 3674
	 * Zone reclaim reclaims unmapped file backed pages and
	 * slab pages if we are over the defined limits.
3675
	 *
3676 3677 3678 3679 3680
	 * A small portion of unmapped file backed pages is needed for
	 * file I/O otherwise pages read by file I/O will be immediately
	 * thrown out if the zone is overallocated. So we do not reclaim
	 * if less than a specified percentage of the zone is used by
	 * unmapped file backed pages.
3681
	 */
3682 3683
	if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
	    zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
3684
		return ZONE_RECLAIM_FULL;
3685

3686
	if (!zone_reclaimable(zone))
3687
		return ZONE_RECLAIM_FULL;
3688

3689
	/*
3690
	 * Do not scan if the allocation should not be delayed.
3691
	 */
3692
	if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
3693
		return ZONE_RECLAIM_NOSCAN;
3694 3695 3696 3697 3698 3699 3700

	/*
	 * Only run zone reclaim on the local zone or on zones that do not
	 * have associated processors. This will favor the local processor
	 * over remote processors and spread off node memory allocations
	 * as wide as possible.
	 */
3701
	node_id = zone_to_nid(zone);
3702
	if (node_state(node_id, N_CPU) && node_id != numa_node_id())
3703
		return ZONE_RECLAIM_NOSCAN;
3704 3705

	if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
3706 3707
		return ZONE_RECLAIM_NOSCAN;

3708 3709 3710
	ret = __zone_reclaim(zone, gfp_mask, order);
	zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);

3711 3712 3713
	if (!ret)
		count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);

3714
	return ret;
3715
}
3716
#endif
L
Lee Schermerhorn 已提交
3717 3718 3719 3720 3721 3722

/*
 * 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
3723
 * lists vs unevictable list.
L
Lee Schermerhorn 已提交
3724 3725
 *
 * Reasons page might not be evictable:
3726
 * (1) page's mapping marked unevictable
N
Nick Piggin 已提交
3727
 * (2) page is part of an mlocked VMA
3728
 *
L
Lee Schermerhorn 已提交
3729
 */
3730
int page_evictable(struct page *page)
L
Lee Schermerhorn 已提交
3731
{
3732
	return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
L
Lee Schermerhorn 已提交
3733
}
3734

3735
#ifdef CONFIG_SHMEM
3736
/**
3737 3738 3739
 * 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
3740
 *
3741
 * Checks pages for evictability and moves them to the appropriate lru list.
3742 3743
 *
 * This function is only used for SysV IPC SHM_UNLOCK.
3744
 */
3745
void check_move_unevictable_pages(struct page **pages, int nr_pages)
3746
{
3747
	struct lruvec *lruvec;
3748 3749 3750 3751
	struct zone *zone = NULL;
	int pgscanned = 0;
	int pgrescued = 0;
	int i;
3752

3753 3754 3755
	for (i = 0; i < nr_pages; i++) {
		struct page *page = pages[i];
		struct zone *pagezone;
3756

3757 3758 3759 3760 3761 3762 3763 3764
		pgscanned++;
		pagezone = page_zone(page);
		if (pagezone != zone) {
			if (zone)
				spin_unlock_irq(&zone->lru_lock);
			zone = pagezone;
			spin_lock_irq(&zone->lru_lock);
		}
3765
		lruvec = mem_cgroup_page_lruvec(page, zone);
3766

3767 3768
		if (!PageLRU(page) || !PageUnevictable(page))
			continue;
3769

3770
		if (page_evictable(page)) {
3771 3772
			enum lru_list lru = page_lru_base_type(page);

3773
			VM_BUG_ON_PAGE(PageActive(page), page);
3774
			ClearPageUnevictable(page);
3775 3776
			del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
			add_page_to_lru_list(page, lruvec, lru);
3777
			pgrescued++;
3778
		}
3779
	}
3780

3781 3782 3783 3784
	if (zone) {
		__count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
		__count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
		spin_unlock_irq(&zone->lru_lock);
3785 3786
	}
}
3787
#endif /* CONFIG_SHMEM */
3788

3789
static void warn_scan_unevictable_pages(void)
3790
{
3791
	printk_once(KERN_WARNING
3792
		    "%s: The scan_unevictable_pages sysctl/node-interface has been "
3793
		    "disabled for lack of a legitimate use case.  If you have "
3794 3795
		    "one, please send an email to linux-mm@kvack.org.\n",
		    current->comm);
3796 3797 3798 3799 3800 3801 3802 3803 3804
}

/*
 * scan_unevictable_pages [vm] sysctl handler.  On demand re-scan of
 * all nodes' unevictable lists for evictable pages
 */
unsigned long scan_unevictable_pages;

int scan_unevictable_handler(struct ctl_table *table, int write,
3805
			   void __user *buffer,
3806 3807
			   size_t *length, loff_t *ppos)
{
3808
	warn_scan_unevictable_pages();
3809
	proc_doulongvec_minmax(table, write, buffer, length, ppos);
3810 3811 3812 3813
	scan_unevictable_pages = 0;
	return 0;
}

3814
#ifdef CONFIG_NUMA
3815 3816 3817 3818 3819
/*
 * per node 'scan_unevictable_pages' attribute.  On demand re-scan of
 * a specified node's per zone unevictable lists for evictable pages.
 */

3820 3821
static ssize_t read_scan_unevictable_node(struct device *dev,
					  struct device_attribute *attr,
3822 3823
					  char *buf)
{
3824
	warn_scan_unevictable_pages();
3825 3826 3827
	return sprintf(buf, "0\n");	/* always zero; should fit... */
}

3828 3829
static ssize_t write_scan_unevictable_node(struct device *dev,
					   struct device_attribute *attr,
3830 3831
					const char *buf, size_t count)
{
3832
	warn_scan_unevictable_pages();
3833 3834 3835 3836
	return 1;
}


3837
static DEVICE_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
3838 3839 3840 3841 3842
			read_scan_unevictable_node,
			write_scan_unevictable_node);

int scan_unevictable_register_node(struct node *node)
{
3843
	return device_create_file(&node->dev, &dev_attr_scan_unevictable_pages);
3844 3845 3846 3847
}

void scan_unevictable_unregister_node(struct node *node)
{
3848
	device_remove_file(&node->dev, &dev_attr_scan_unevictable_pages);
3849
}
3850
#endif