vmscan.c 99.7 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/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 "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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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 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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/*
 * Add a shrinker callback to be called from the vm
 */
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void register_shrinker(struct shrinker *shrinker)
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{
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	atomic_long_set(&shrinker->nr_in_batch, 0);
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	down_write(&shrinker_rwsem);
	list_add_tail(&shrinker->list, &shrinker_list);
	up_write(&shrinker_rwsem);
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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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EXPORT_SYMBOL(unregister_shrinker);
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static inline int do_shrinker_shrink(struct shrinker *shrinker,
				     struct shrink_control *sc,
				     unsigned long nr_to_scan)
{
	sc->nr_to_scan = nr_to_scan;
	return (*shrinker->shrink)(shrinker, sc);
}

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#define SHRINK_BATCH 128
/*
 * 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 *shrink,
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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 ret = 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)) {
		/* Assume we'll be able to shrink next time */
		ret = 1;
		goto out;
	}
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	list_for_each_entry(shrinker, &shrinker_list, list) {
		unsigned long long delta;
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		long total_scan;
		long max_pass;
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		int shrink_ret = 0;
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		long nr;
		long new_nr;
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		long batch_size = shrinker->batch ? shrinker->batch
						  : SHRINK_BATCH;
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		max_pass = do_shrinker_shrink(shrinker, shrink, 0);
		if (max_pass <= 0)
			continue;

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		/*
		 * 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.
		 */
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		nr = atomic_long_xchg(&shrinker->nr_in_batch, 0);
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		total_scan = nr;
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		delta = (4 * nr_pages_scanned) / shrinker->seeks;
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		delta *= max_pass;
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		do_div(delta, lru_pages + 1);
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		total_scan += delta;
		if (total_scan < 0) {
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			printk(KERN_ERR "shrink_slab: %pF negative objects to "
			       "delete nr=%ld\n",
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			       shrinker->shrink, total_scan);
			total_scan = max_pass;
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		}

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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 >>>
		 * max_pass.  This is bad for sustaining a working set in
		 * memory.
		 *
		 * Hence only allow the shrinker to scan the entire cache when
		 * a large delta change is calculated directly.
		 */
		if (delta < max_pass / 4)
			total_scan = min(total_scan, max_pass / 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 > max_pass * 2)
			total_scan = max_pass * 2;
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		trace_mm_shrink_slab_start(shrinker, shrink, nr,
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					nr_pages_scanned, lru_pages,
					max_pass, delta, total_scan);

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		while (total_scan >= batch_size) {
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			int nr_before;
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			nr_before = do_shrinker_shrink(shrinker, shrink, 0);
			shrink_ret = do_shrinker_shrink(shrinker, shrink,
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							batch_size);
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			if (shrink_ret == -1)
				break;
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			if (shrink_ret < nr_before)
				ret += nr_before - shrink_ret;
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			count_vm_events(SLABS_SCANNED, batch_size);
			total_scan -= batch_size;
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			cond_resched();
		}

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		/*
		 * move the unused scan count back into the shrinker in a
		 * manner that handles concurrent updates. If we exhausted the
		 * scan, there is no need to do an update.
		 */
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		if (total_scan > 0)
			new_nr = atomic_long_add_return(total_scan,
					&shrinker->nr_in_batch);
		else
			new_nr = atomic_long_read(&shrinker->nr_in_batch);
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		trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr);
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	}
	up_read(&shrinker_rwsem);
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out:
	cond_resched();
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	return ret;
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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)
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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 *);

		freepage = mapping->a_ops->freepage;

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		__delete_from_page_cache(page);
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		spin_unlock_irq(&mapping->tree_lock);
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		mem_cgroup_uncharge_cache_page(page);
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		if (freepage != NULL)
			freepage(page);
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	}

	return 1;

cannot_free:
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	spin_unlock_irq(&mapping->tree_lock);
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	return 0;
}

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/*
 * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
 * someone else has a ref on the page, abort and return 0.  If it was
 * successfully detached, return 1.  Assumes the caller has a single ref on
 * this page.
 */
int remove_mapping(struct address_space *mapping, struct page *page)
{
	if (__remove_mapping(mapping, page)) {
		/*
		 * 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;
}

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/**
 * 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)
{
	int lru;
	int active = !!TestClearPageActive(page);
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	int was_unevictable = PageUnevictable(page);
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	VM_BUG_ON(PageLRU(page));

redo:
	ClearPageUnevictable(page);

556
	if (page_evictable(page)) {
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		/*
		 * 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.
		 */
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		lru = active + page_lru_base_type(page);
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		lru_cache_add_lru(page, lru);
	} else {
		/*
		 * Put unevictable pages directly on zone's unevictable
		 * list.
		 */
		lru = LRU_UNEVICTABLE;
		add_page_to_unevictable_list(page);
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		/*
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		 * 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
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		 * isolation/check_move_unevictable_pages,
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		 * we see PG_mlocked/AS_UNEVICTABLE cleared below and move
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		 * the page back to the evictable list.
		 *
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		 * The other side is TestClearPageMlocked() or shmem_lock().
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		 */
		smp_mb();
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	}

	/*
	 * 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.
	 */
590
	if (lru == LRU_UNEVICTABLE && page_evictable(page)) {
L
Lee Schermerhorn 已提交
591 592 593 594 595 596 597 598 599 600
		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.
		 */
	}

601 602 603 604 605
	if (was_unevictable && lru != LRU_UNEVICTABLE)
		count_vm_event(UNEVICTABLE_PGRESCUED);
	else if (!was_unevictable && lru == LRU_UNEVICTABLE)
		count_vm_event(UNEVICTABLE_PGCULLED);

L
Lee Schermerhorn 已提交
606 607 608
	put_page(page);		/* drop ref from isolate */
}

609 610 611
enum page_references {
	PAGEREF_RECLAIM,
	PAGEREF_RECLAIM_CLEAN,
612
	PAGEREF_KEEP,
613 614 615 616 617 618
	PAGEREF_ACTIVATE,
};

static enum page_references page_check_references(struct page *page,
						  struct scan_control *sc)
{
619
	int referenced_ptes, referenced_page;
620 621
	unsigned long vm_flags;

622 623
	referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
					  &vm_flags);
624
	referenced_page = TestClearPageReferenced(page);
625 626 627 628 629 630 631 632

	/*
	 * 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;

633
	if (referenced_ptes) {
634
		if (PageSwapBacked(page))
635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651
			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);

652
		if (referenced_page || referenced_ptes > 1)
653 654
			return PAGEREF_ACTIVATE;

655 656 657 658 659 660
		/*
		 * Activate file-backed executable pages after first usage.
		 */
		if (vm_flags & VM_EXEC)
			return PAGEREF_ACTIVATE;

661 662
		return PAGEREF_KEEP;
	}
663 664

	/* Reclaim if clean, defer dirty pages to writeback */
665
	if (referenced_page && !PageSwapBacked(page))
666 667 668
		return PAGEREF_RECLAIM_CLEAN;

	return PAGEREF_RECLAIM;
669 670
}

L
Linus Torvalds 已提交
671
/*
A
Andrew Morton 已提交
672
 * shrink_page_list() returns the number of reclaimed pages
L
Linus Torvalds 已提交
673
 */
A
Andrew Morton 已提交
674
static unsigned long shrink_page_list(struct list_head *page_list,
675
				      struct zone *zone,
676
				      struct scan_control *sc,
677
				      enum ttu_flags ttu_flags,
678
				      unsigned long *ret_nr_dirty,
679 680
				      unsigned long *ret_nr_writeback,
				      bool force_reclaim)
L
Linus Torvalds 已提交
681 682
{
	LIST_HEAD(ret_pages);
683
	LIST_HEAD(free_pages);
L
Linus Torvalds 已提交
684
	int pgactivate = 0;
685 686
	unsigned long nr_dirty = 0;
	unsigned long nr_congested = 0;
687
	unsigned long nr_reclaimed = 0;
688
	unsigned long nr_writeback = 0;
L
Linus Torvalds 已提交
689 690 691

	cond_resched();

692
	mem_cgroup_uncharge_start();
L
Linus Torvalds 已提交
693 694 695 696
	while (!list_empty(page_list)) {
		struct address_space *mapping;
		struct page *page;
		int may_enter_fs;
697
		enum page_references references = PAGEREF_RECLAIM_CLEAN;
L
Linus Torvalds 已提交
698 699 700 701 702 703

		cond_resched();

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

N
Nick Piggin 已提交
704
		if (!trylock_page(page))
L
Linus Torvalds 已提交
705 706
			goto keep;

N
Nick Piggin 已提交
707
		VM_BUG_ON(PageActive(page));
708
		VM_BUG_ON(page_zone(page) != zone);
L
Linus Torvalds 已提交
709 710

		sc->nr_scanned++;
711

712
		if (unlikely(!page_evictable(page)))
N
Nick Piggin 已提交
713
			goto cull_mlocked;
L
Lee Schermerhorn 已提交
714

715
		if (!sc->may_unmap && page_mapped(page))
716 717
			goto keep_locked;

L
Linus Torvalds 已提交
718 719 720 721
		/* Double the slab pressure for mapped and swapcache pages */
		if (page_mapped(page) || PageSwapCache(page))
			sc->nr_scanned++;

722 723 724 725
		may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
			(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));

		if (PageWriteback(page)) {
726 727 728
			/*
			 * memcg doesn't have any dirty pages throttling so we
			 * could easily OOM just because too many pages are in
729
			 * writeback and there is nothing else to reclaim.
730
			 *
731
			 * Check __GFP_IO, certainly because a loop driver
732 733 734 735
			 * 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.
736 737 738 739 740 741
			 *
			 * 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.
742
			 */
743 744 745 746 747 748 749 750 751 752 753 754 755 756
			if (global_reclaim(sc) ||
			    !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);
757
				nr_writeback++;
758
				goto keep_locked;
759
			}
760
			wait_on_page_writeback(page);
761
		}
L
Linus Torvalds 已提交
762

763 764 765
		if (!force_reclaim)
			references = page_check_references(page, sc);

766 767
		switch (references) {
		case PAGEREF_ACTIVATE:
L
Linus Torvalds 已提交
768
			goto activate_locked;
769 770
		case PAGEREF_KEEP:
			goto keep_locked;
771 772 773 774
		case PAGEREF_RECLAIM:
		case PAGEREF_RECLAIM_CLEAN:
			; /* try to reclaim the page below */
		}
L
Linus Torvalds 已提交
775 776 777 778 779

		/*
		 * Anonymous process memory has backing store?
		 * Try to allocate it some swap space here.
		 */
N
Nick Piggin 已提交
780
		if (PageAnon(page) && !PageSwapCache(page)) {
781 782
			if (!(sc->gfp_mask & __GFP_IO))
				goto keep_locked;
783
			if (!add_to_swap(page))
L
Linus Torvalds 已提交
784
				goto activate_locked;
785
			may_enter_fs = 1;
N
Nick Piggin 已提交
786
		}
L
Linus Torvalds 已提交
787 788 789 790 791 792 793 794

		mapping = page_mapping(page);

		/*
		 * The page is mapped into the page tables of one or more
		 * processes. Try to unmap it here.
		 */
		if (page_mapped(page) && mapping) {
795
			switch (try_to_unmap(page, ttu_flags)) {
L
Linus Torvalds 已提交
796 797 798 799
			case SWAP_FAIL:
				goto activate_locked;
			case SWAP_AGAIN:
				goto keep_locked;
N
Nick Piggin 已提交
800 801
			case SWAP_MLOCK:
				goto cull_mlocked;
L
Linus Torvalds 已提交
802 803 804 805 806 807
			case SWAP_SUCCESS:
				; /* try to free the page below */
			}
		}

		if (PageDirty(page)) {
808 809
			nr_dirty++;

810 811
			/*
			 * Only kswapd can writeback filesystem pages to
812 813
			 * avoid risk of stack overflow but do not writeback
			 * unless under significant pressure.
814
			 */
815
			if (page_is_file_cache(page) &&
816 817
					(!current_is_kswapd() ||
					 sc->priority >= DEF_PRIORITY - 2)) {
818 819 820 821 822 823 824 825 826
				/*
				 * 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);

827 828 829
				goto keep_locked;
			}

830
			if (references == PAGEREF_RECLAIM_CLEAN)
L
Linus Torvalds 已提交
831
				goto keep_locked;
832
			if (!may_enter_fs)
L
Linus Torvalds 已提交
833
				goto keep_locked;
834
			if (!sc->may_writepage)
L
Linus Torvalds 已提交
835 836 837
				goto keep_locked;

			/* Page is dirty, try to write it out here */
838
			switch (pageout(page, mapping, sc)) {
L
Linus Torvalds 已提交
839
			case PAGE_KEEP:
840
				nr_congested++;
L
Linus Torvalds 已提交
841 842 843 844
				goto keep_locked;
			case PAGE_ACTIVATE:
				goto activate_locked;
			case PAGE_SUCCESS:
845
				if (PageWriteback(page))
846
					goto keep;
847
				if (PageDirty(page))
L
Linus Torvalds 已提交
848
					goto keep;
849

L
Linus Torvalds 已提交
850 851 852 853
				/*
				 * A synchronous write - probably a ramdisk.  Go
				 * ahead and try to reclaim the page.
				 */
N
Nick Piggin 已提交
854
				if (!trylock_page(page))
L
Linus Torvalds 已提交
855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873
					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
874
		 * will do this, as well as the blockdev mapping.
L
Linus Torvalds 已提交
875 876 877 878 879 880 881 882 883 884
		 * 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.
		 */
885
		if (page_has_private(page)) {
L
Linus Torvalds 已提交
886 887
			if (!try_to_release_page(page, sc->gfp_mask))
				goto activate_locked;
N
Nick Piggin 已提交
888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903
			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
904 905
		}

N
Nick Piggin 已提交
906
		if (!mapping || !__remove_mapping(mapping, page))
907
			goto keep_locked;
L
Linus Torvalds 已提交
908

N
Nick Piggin 已提交
909 910 911 912 913 914 915 916
		/*
		 * 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
917
free_it:
918
		nr_reclaimed++;
919 920 921 922 923 924

		/*
		 * 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
925 926
		continue;

N
Nick Piggin 已提交
927
cull_mlocked:
928 929
		if (PageSwapCache(page))
			try_to_free_swap(page);
N
Nick Piggin 已提交
930 931 932 933
		unlock_page(page);
		putback_lru_page(page);
		continue;

L
Linus Torvalds 已提交
934
activate_locked:
935 936
		/* Not a candidate for swapping, so reclaim swap space. */
		if (PageSwapCache(page) && vm_swap_full())
937
			try_to_free_swap(page);
L
Lee Schermerhorn 已提交
938
		VM_BUG_ON(PageActive(page));
L
Linus Torvalds 已提交
939 940 941 942 943 944
		SetPageActive(page);
		pgactivate++;
keep_locked:
		unlock_page(page);
keep:
		list_add(&page->lru, &ret_pages);
N
Nick Piggin 已提交
945
		VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
L
Linus Torvalds 已提交
946
	}
947

948 949 950 951 952 953
	/*
	 * Tag a zone as congested if all the dirty pages encountered were
	 * backed by a congested BDI. In this case, reclaimers should just
	 * back off and wait for congestion to clear because further reclaim
	 * will encounter the same problem
	 */
954
	if (nr_dirty && nr_dirty == nr_congested && global_reclaim(sc))
955
		zone_set_flag(zone, ZONE_CONGESTED);
956

957
	free_hot_cold_page_list(&free_pages, 1);
958

L
Linus Torvalds 已提交
959
	list_splice(&ret_pages, page_list);
960
	count_vm_events(PGACTIVATE, pgactivate);
961
	mem_cgroup_uncharge_end();
962 963
	*ret_nr_dirty += nr_dirty;
	*ret_nr_writeback += nr_writeback;
964
	return nr_reclaimed;
L
Linus Torvalds 已提交
965 966
}

967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993
unsigned long reclaim_clean_pages_from_list(struct zone *zone,
					    struct list_head *page_list)
{
	struct scan_control sc = {
		.gfp_mask = GFP_KERNEL,
		.priority = DEF_PRIORITY,
		.may_unmap = 1,
	};
	unsigned long ret, dummy1, dummy2;
	struct page *page, *next;
	LIST_HEAD(clean_pages);

	list_for_each_entry_safe(page, next, page_list, lru) {
		if (page_is_file_cache(page) && !PageDirty(page)) {
			ClearPageActive(page);
			list_move(&page->lru, &clean_pages);
		}
	}

	ret = shrink_page_list(&clean_pages, zone, &sc,
				TTU_UNMAP|TTU_IGNORE_ACCESS,
				&dummy1, &dummy2, true);
	list_splice(&clean_pages, page_list);
	__mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret);
	return ret;
}

A
Andy Whitcroft 已提交
994 995 996 997 998 999 1000 1001 1002 1003
/*
 * 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.
 */
1004
int __isolate_lru_page(struct page *page, isolate_mode_t mode)
A
Andy Whitcroft 已提交
1005 1006 1007 1008 1009 1010 1011
{
	int ret = -EINVAL;

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

M
Minchan Kim 已提交
1012 1013
	/* Compaction should not handle unevictable pages but CMA can do so */
	if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
L
Lee Schermerhorn 已提交
1014 1015
		return ret;

A
Andy Whitcroft 已提交
1016
	ret = -EBUSY;
K
KAMEZAWA Hiroyuki 已提交
1017

1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050
	/*
	 * 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;
		}
	}
1051

1052 1053 1054
	if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
		return ret;

A
Andy Whitcroft 已提交
1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067
	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
1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078
/*
 * 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.
1079
 * @lruvec:	The LRU vector to pull pages from.
L
Linus Torvalds 已提交
1080
 * @dst:	The temp list to put pages on to.
H
Hugh Dickins 已提交
1081
 * @nr_scanned:	The number of pages that were scanned.
1082
 * @sc:		The scan_control struct for this reclaim session
A
Andy Whitcroft 已提交
1083
 * @mode:	One of the LRU isolation modes
1084
 * @lru:	LRU list id for isolating
L
Linus Torvalds 已提交
1085 1086 1087
 *
 * returns how many pages were moved onto *@dst.
 */
1088
static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1089
		struct lruvec *lruvec, struct list_head *dst,
1090
		unsigned long *nr_scanned, struct scan_control *sc,
1091
		isolate_mode_t mode, enum lru_list lru)
L
Linus Torvalds 已提交
1092
{
H
Hugh Dickins 已提交
1093
	struct list_head *src = &lruvec->lists[lru];
1094
	unsigned long nr_taken = 0;
1095
	unsigned long scan;
L
Linus Torvalds 已提交
1096

1097
	for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
A
Andy Whitcroft 已提交
1098
		struct page *page;
1099
		int nr_pages;
A
Andy Whitcroft 已提交
1100

L
Linus Torvalds 已提交
1101 1102 1103
		page = lru_to_page(src);
		prefetchw_prev_lru_page(page, src, flags);

N
Nick Piggin 已提交
1104
		VM_BUG_ON(!PageLRU(page));
N
Nick Piggin 已提交
1105

1106
		switch (__isolate_lru_page(page, mode)) {
A
Andy Whitcroft 已提交
1107
		case 0:
1108 1109
			nr_pages = hpage_nr_pages(page);
			mem_cgroup_update_lru_size(lruvec, lru, -nr_pages);
A
Andy Whitcroft 已提交
1110
			list_move(&page->lru, dst);
1111
			nr_taken += nr_pages;
A
Andy Whitcroft 已提交
1112 1113 1114 1115 1116 1117
			break;

		case -EBUSY:
			/* else it is being freed elsewhere */
			list_move(&page->lru, src);
			continue;
1118

A
Andy Whitcroft 已提交
1119 1120 1121
		default:
			BUG();
		}
L
Linus Torvalds 已提交
1122 1123
	}

H
Hugh Dickins 已提交
1124
	*nr_scanned = scan;
H
Hugh Dickins 已提交
1125 1126
	trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
				    nr_taken, mode, is_file_lru(lru));
L
Linus Torvalds 已提交
1127 1128 1129
	return nr_taken;
}

1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140
/**
 * 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
1141 1142 1143
 * 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.
1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158
 *
 * 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;

1159 1160
	VM_BUG_ON(!page_count(page));

1161 1162
	if (PageLRU(page)) {
		struct zone *zone = page_zone(page);
1163
		struct lruvec *lruvec;
1164 1165

		spin_lock_irq(&zone->lru_lock);
1166
		lruvec = mem_cgroup_page_lruvec(page, zone);
1167
		if (PageLRU(page)) {
L
Lee Schermerhorn 已提交
1168
			int lru = page_lru(page);
1169
			get_page(page);
1170
			ClearPageLRU(page);
1171 1172
			del_page_from_lru_list(page, lruvec, lru);
			ret = 0;
1173 1174 1175 1176 1177 1178
		}
		spin_unlock_irq(&zone->lru_lock);
	}
	return ret;
}

1179
/*
F
Fengguang Wu 已提交
1180 1181 1182 1183 1184
 * 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.
1185 1186 1187 1188 1189 1190 1191 1192 1193
 */
static int too_many_isolated(struct zone *zone, int file,
		struct scan_control *sc)
{
	unsigned long inactive, isolated;

	if (current_is_kswapd())
		return 0;

1194
	if (!global_reclaim(sc))
1195 1196 1197 1198 1199 1200 1201 1202 1203 1204
		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);
	}

1205 1206 1207 1208 1209 1210 1211 1212
	/*
	 * 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;

1213 1214 1215
	return isolated > inactive;
}

1216
static noinline_for_stack void
H
Hugh Dickins 已提交
1217
putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
1218
{
1219 1220
	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
	struct zone *zone = lruvec_zone(lruvec);
1221
	LIST_HEAD(pages_to_free);
1222 1223 1224 1225 1226

	/*
	 * Put back any unfreeable pages.
	 */
	while (!list_empty(page_list)) {
1227
		struct page *page = lru_to_page(page_list);
1228
		int lru;
1229

1230 1231
		VM_BUG_ON(PageLRU(page));
		list_del(&page->lru);
1232
		if (unlikely(!page_evictable(page))) {
1233 1234 1235 1236 1237
			spin_unlock_irq(&zone->lru_lock);
			putback_lru_page(page);
			spin_lock_irq(&zone->lru_lock);
			continue;
		}
1238 1239 1240

		lruvec = mem_cgroup_page_lruvec(page, zone);

1241
		SetPageLRU(page);
1242
		lru = page_lru(page);
1243 1244
		add_page_to_lru_list(page, lruvec, lru);

1245 1246
		if (is_active_lru(lru)) {
			int file = is_file_lru(lru);
1247 1248
			int numpages = hpage_nr_pages(page);
			reclaim_stat->recent_rotated[file] += numpages;
1249
		}
1250 1251 1252
		if (put_page_testzero(page)) {
			__ClearPageLRU(page);
			__ClearPageActive(page);
1253
			del_page_from_lru_list(page, lruvec, lru);
1254 1255 1256 1257 1258 1259 1260

			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);
1261 1262 1263
		}
	}

1264 1265 1266 1267
	/*
	 * To save our caller's stack, now use input list for pages to free.
	 */
	list_splice(&pages_to_free, page_list);
1268 1269
}

L
Linus Torvalds 已提交
1270
/*
A
Andrew Morton 已提交
1271 1272
 * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
 * of reclaimed pages
L
Linus Torvalds 已提交
1273
 */
1274
static noinline_for_stack unsigned long
1275
shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1276
		     struct scan_control *sc, enum lru_list lru)
L
Linus Torvalds 已提交
1277 1278
{
	LIST_HEAD(page_list);
1279
	unsigned long nr_scanned;
1280
	unsigned long nr_reclaimed = 0;
1281
	unsigned long nr_taken;
1282 1283
	unsigned long nr_dirty = 0;
	unsigned long nr_writeback = 0;
1284
	isolate_mode_t isolate_mode = 0;
1285
	int file = is_file_lru(lru);
1286 1287
	struct zone *zone = lruvec_zone(lruvec);
	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1288

1289
	while (unlikely(too_many_isolated(zone, file, sc))) {
1290
		congestion_wait(BLK_RW_ASYNC, HZ/10);
1291 1292 1293 1294 1295 1296

		/* 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
1297
	lru_add_drain();
1298 1299

	if (!sc->may_unmap)
1300
		isolate_mode |= ISOLATE_UNMAPPED;
1301
	if (!sc->may_writepage)
1302
		isolate_mode |= ISOLATE_CLEAN;
1303

L
Linus Torvalds 已提交
1304
	spin_lock_irq(&zone->lru_lock);
1305

1306 1307
	nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
				     &nr_scanned, sc, isolate_mode, lru);
1308 1309 1310 1311

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

1312
	if (global_reclaim(sc)) {
1313 1314
		zone->pages_scanned += nr_scanned;
		if (current_is_kswapd())
H
Hugh Dickins 已提交
1315
			__count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scanned);
1316
		else
H
Hugh Dickins 已提交
1317
			__count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scanned);
1318
	}
1319
	spin_unlock_irq(&zone->lru_lock);
1320

1321
	if (nr_taken == 0)
1322
		return 0;
A
Andy Whitcroft 已提交
1323

1324 1325
	nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
					&nr_dirty, &nr_writeback, false);
1326

1327 1328
	spin_lock_irq(&zone->lru_lock);

1329
	reclaim_stat->recent_scanned[file] += nr_taken;
1330

Y
Ying Han 已提交
1331 1332 1333 1334 1335 1336 1337 1338
	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
1339

1340
	putback_inactive_pages(lruvec, &page_list);
1341

1342
	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1343 1344 1345 1346

	spin_unlock_irq(&zone->lru_lock);

	free_hot_cold_page_list(&page_list, 1);
1347

1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370
	/*
	 * 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.
	 *
	 * This scales the number of dirty pages that must be under writeback
	 * before throttling depending on priority. It is a simple backoff
	 * function that has the most effect in the range DEF_PRIORITY to
	 * DEF_PRIORITY-2 which is the priority reclaim is considered to be
	 * in trouble and reclaim is considered to be in trouble.
	 *
	 * DEF_PRIORITY   100% isolated pages must be PageWriteback to throttle
	 * DEF_PRIORITY-1  50% must be PageWriteback
	 * DEF_PRIORITY-2  25% must be PageWriteback, kswapd in trouble
	 * ...
	 * DEF_PRIORITY-6 For SWAP_CLUSTER_MAX isolated pages, throttle if any
	 *                     isolated page is PageWriteback
	 */
1371 1372
	if (nr_writeback && nr_writeback >=
			(nr_taken >> (DEF_PRIORITY - sc->priority)))
1373 1374
		wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);

1375 1376 1377
	trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
		zone_idx(zone),
		nr_scanned, nr_reclaimed,
1378
		sc->priority,
M
Mel Gorman 已提交
1379
		trace_shrink_flags(file));
1380
	return nr_reclaimed;
L
Linus Torvalds 已提交
1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399
}

/*
 * 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.
 */
1400

1401
static void move_active_pages_to_lru(struct lruvec *lruvec,
1402
				     struct list_head *list,
1403
				     struct list_head *pages_to_free,
1404 1405
				     enum lru_list lru)
{
1406
	struct zone *zone = lruvec_zone(lruvec);
1407 1408
	unsigned long pgmoved = 0;
	struct page *page;
1409
	int nr_pages;
1410 1411 1412

	while (!list_empty(list)) {
		page = lru_to_page(list);
1413
		lruvec = mem_cgroup_page_lruvec(page, zone);
1414 1415 1416 1417

		VM_BUG_ON(PageLRU(page));
		SetPageLRU(page);

1418 1419
		nr_pages = hpage_nr_pages(page);
		mem_cgroup_update_lru_size(lruvec, lru, nr_pages);
1420
		list_move(&page->lru, &lruvec->lists[lru]);
1421
		pgmoved += nr_pages;
1422

1423 1424 1425
		if (put_page_testzero(page)) {
			__ClearPageLRU(page);
			__ClearPageActive(page);
1426
			del_page_from_lru_list(page, lruvec, lru);
1427 1428 1429 1430 1431 1432 1433

			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);
1434 1435 1436 1437 1438 1439
		}
	}
	__mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
	if (!is_active_lru(lru))
		__count_vm_events(PGDEACTIVATE, pgmoved);
}
1440

H
Hugh Dickins 已提交
1441
static void shrink_active_list(unsigned long nr_to_scan,
1442
			       struct lruvec *lruvec,
1443
			       struct scan_control *sc,
1444
			       enum lru_list lru)
L
Linus Torvalds 已提交
1445
{
1446
	unsigned long nr_taken;
H
Hugh Dickins 已提交
1447
	unsigned long nr_scanned;
1448
	unsigned long vm_flags;
L
Linus Torvalds 已提交
1449
	LIST_HEAD(l_hold);	/* The pages which were snipped off */
1450
	LIST_HEAD(l_active);
1451
	LIST_HEAD(l_inactive);
L
Linus Torvalds 已提交
1452
	struct page *page;
1453
	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1454
	unsigned long nr_rotated = 0;
1455
	isolate_mode_t isolate_mode = 0;
1456
	int file = is_file_lru(lru);
1457
	struct zone *zone = lruvec_zone(lruvec);
L
Linus Torvalds 已提交
1458 1459

	lru_add_drain();
1460 1461

	if (!sc->may_unmap)
1462
		isolate_mode |= ISOLATE_UNMAPPED;
1463
	if (!sc->may_writepage)
1464
		isolate_mode |= ISOLATE_CLEAN;
1465

L
Linus Torvalds 已提交
1466
	spin_lock_irq(&zone->lru_lock);
1467

1468 1469
	nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
				     &nr_scanned, sc, isolate_mode, lru);
1470
	if (global_reclaim(sc))
H
Hugh Dickins 已提交
1471
		zone->pages_scanned += nr_scanned;
1472

1473
	reclaim_stat->recent_scanned[file] += nr_taken;
1474

H
Hugh Dickins 已提交
1475
	__count_zone_vm_events(PGREFILL, zone, nr_scanned);
1476
	__mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
K
KOSAKI Motohiro 已提交
1477
	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
L
Linus Torvalds 已提交
1478 1479 1480 1481 1482 1483
	spin_unlock_irq(&zone->lru_lock);

	while (!list_empty(&l_hold)) {
		cond_resched();
		page = lru_to_page(&l_hold);
		list_del(&page->lru);
1484

1485
		if (unlikely(!page_evictable(page))) {
L
Lee Schermerhorn 已提交
1486 1487 1488 1489
			putback_lru_page(page);
			continue;
		}

1490 1491 1492 1493 1494 1495 1496 1497
		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);
			}
		}

1498 1499
		if (page_referenced(page, 0, sc->target_mem_cgroup,
				    &vm_flags)) {
1500
			nr_rotated += hpage_nr_pages(page);
1501 1502 1503 1504 1505 1506 1507 1508 1509
			/*
			 * 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.
			 */
1510
			if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1511 1512 1513 1514
				list_add(&page->lru, &l_active);
				continue;
			}
		}
1515

1516
		ClearPageActive(page);	/* we are de-activating */
L
Linus Torvalds 已提交
1517 1518 1519
		list_add(&page->lru, &l_inactive);
	}

1520
	/*
1521
	 * Move pages back to the lru list.
1522
	 */
1523
	spin_lock_irq(&zone->lru_lock);
1524
	/*
1525 1526 1527 1528
	 * 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.
1529
	 */
1530
	reclaim_stat->recent_rotated[file] += nr_rotated;
1531

1532 1533
	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
1534
	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1535
	spin_unlock_irq(&zone->lru_lock);
1536 1537

	free_hot_cold_page_list(&l_hold, 1);
L
Linus Torvalds 已提交
1538 1539
}

1540
#ifdef CONFIG_SWAP
1541
static int inactive_anon_is_low_global(struct zone *zone)
1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553
{
	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;
}

1554 1555
/**
 * inactive_anon_is_low - check if anonymous pages need to be deactivated
1556
 * @lruvec: LRU vector to check
1557 1558 1559 1560
 *
 * Returns true if the zone does not have enough inactive anon pages,
 * meaning some active anon pages need to be deactivated.
 */
1561
static int inactive_anon_is_low(struct lruvec *lruvec)
1562
{
1563 1564 1565 1566 1567 1568 1569
	/*
	 * If we don't have swap space, anonymous page deactivation
	 * is pointless.
	 */
	if (!total_swap_pages)
		return 0;

1570
	if (!mem_cgroup_disabled())
1571
		return mem_cgroup_inactive_anon_is_low(lruvec);
1572

1573
	return inactive_anon_is_low_global(lruvec_zone(lruvec));
1574
}
1575
#else
1576
static inline int inactive_anon_is_low(struct lruvec *lruvec)
1577 1578 1579 1580
{
	return 0;
}
#endif
1581

1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593
static int inactive_file_is_low_global(struct zone *zone)
{
	unsigned long active, inactive;

	active = zone_page_state(zone, NR_ACTIVE_FILE);
	inactive = zone_page_state(zone, NR_INACTIVE_FILE);

	return (active > inactive);
}

/**
 * inactive_file_is_low - check if file pages need to be deactivated
1594
 * @lruvec: LRU vector to check
1595 1596 1597 1598 1599 1600 1601 1602 1603 1604 1605
 *
 * 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.
 */
1606
static int inactive_file_is_low(struct lruvec *lruvec)
1607
{
1608
	if (!mem_cgroup_disabled())
1609
		return mem_cgroup_inactive_file_is_low(lruvec);
1610

1611
	return inactive_file_is_low_global(lruvec_zone(lruvec));
1612 1613
}

H
Hugh Dickins 已提交
1614
static int inactive_list_is_low(struct lruvec *lruvec, enum lru_list lru)
1615
{
H
Hugh Dickins 已提交
1616
	if (is_file_lru(lru))
1617
		return inactive_file_is_low(lruvec);
1618
	else
1619
		return inactive_anon_is_low(lruvec);
1620 1621
}

1622
static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1623
				 struct lruvec *lruvec, struct scan_control *sc)
1624
{
1625
	if (is_active_lru(lru)) {
H
Hugh Dickins 已提交
1626
		if (inactive_list_is_low(lruvec, lru))
1627
			shrink_active_list(nr_to_scan, lruvec, sc, lru);
1628 1629 1630
		return 0;
	}

1631
	return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
1632 1633
}

1634
static int vmscan_swappiness(struct scan_control *sc)
1635
{
1636
	if (global_reclaim(sc))
1637
		return vm_swappiness;
1638
	return mem_cgroup_swappiness(sc->target_mem_cgroup);
1639 1640
}

1641 1642 1643 1644 1645 1646
/*
 * 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
1647 1648
 * 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
1649
 */
1650
static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
1651
			   unsigned long *nr)
1652 1653 1654 1655
{
	unsigned long anon, file, free;
	unsigned long anon_prio, file_prio;
	unsigned long ap, fp;
1656
	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1657
	u64 fraction[2], denominator;
H
Hugh Dickins 已提交
1658
	enum lru_list lru;
1659
	int noswap = 0;
1660
	bool force_scan = false;
1661
	struct zone *zone = lruvec_zone(lruvec);
1662

1663 1664 1665 1666 1667 1668 1669 1670 1671 1672
	/*
	 * 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.
	 */
1673
	if (current_is_kswapd() && zone->all_unreclaimable)
1674
		force_scan = true;
1675
	if (!global_reclaim(sc))
1676
		force_scan = true;
1677 1678 1679 1680 1681 1682 1683 1684 1685

	/* If we have no swap space, do not bother scanning anon pages. */
	if (!sc->may_swap || (nr_swap_pages <= 0)) {
		noswap = 1;
		fraction[0] = 0;
		fraction[1] = 1;
		denominator = 1;
		goto out;
	}
1686

1687 1688 1689 1690
	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);
1691

1692
	if (global_reclaim(sc)) {
1693 1694
		free  = zone_page_state(zone, NR_FREE_PAGES);
		if (unlikely(file + free <= high_wmark_pages(zone))) {
1695 1696 1697 1698
			/*
			 * If we have very few page cache pages, force-scan
			 * anon pages.
			 */
1699 1700 1701 1702
			fraction[0] = 1;
			fraction[1] = 0;
			denominator = 1;
			goto out;
1703
		}
1704 1705
	}

1706 1707 1708 1709 1710 1711 1712 1713 1714 1715 1716
	/*
	 * There is enough inactive page cache, do not reclaim
	 * anything from the anonymous working set right now.
	 */
	if (!inactive_file_is_low(lruvec)) {
		fraction[0] = 0;
		fraction[1] = 1;
		denominator = 1;
		goto out;
	}

1717 1718 1719 1720
	/*
	 * With swappiness at 100, anonymous and file have the same priority.
	 * This scanning priority is essentially the inverse of IO cost.
	 */
1721
	anon_prio = vmscan_swappiness(sc);
H
Hugh Dickins 已提交
1722
	file_prio = 200 - anon_prio;
1723

1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734
	/*
	 * 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]
	 */
1735
	spin_lock_irq(&zone->lru_lock);
1736 1737 1738
	if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
		reclaim_stat->recent_scanned[0] /= 2;
		reclaim_stat->recent_rotated[0] /= 2;
1739 1740
	}

1741 1742 1743
	if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
		reclaim_stat->recent_scanned[1] /= 2;
		reclaim_stat->recent_rotated[1] /= 2;
1744 1745 1746
	}

	/*
1747 1748 1749
	 * 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.
1750
	 */
1751
	ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
1752
	ap /= reclaim_stat->recent_rotated[0] + 1;
1753

1754
	fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
1755
	fp /= reclaim_stat->recent_rotated[1] + 1;
1756
	spin_unlock_irq(&zone->lru_lock);
1757

1758 1759 1760 1761
	fraction[0] = ap;
	fraction[1] = fp;
	denominator = ap + fp + 1;
out:
H
Hugh Dickins 已提交
1762 1763
	for_each_evictable_lru(lru) {
		int file = is_file_lru(lru);
1764
		unsigned long scan;
1765

1766
		scan = get_lru_size(lruvec, lru);
1767 1768
		if (sc->priority || noswap || !vmscan_swappiness(sc)) {
			scan >>= sc->priority;
1769 1770
			if (!scan && force_scan)
				scan = SWAP_CLUSTER_MAX;
1771 1772
			scan = div64_u64(scan * fraction[file], denominator);
		}
H
Hugh Dickins 已提交
1773
		nr[lru] = scan;
1774
	}
1775
}
1776

M
Mel Gorman 已提交
1777
/* Use reclaim/compaction for costly allocs or under memory pressure */
1778
static bool in_reclaim_compaction(struct scan_control *sc)
M
Mel Gorman 已提交
1779
{
1780
	if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
M
Mel Gorman 已提交
1781
			(sc->order > PAGE_ALLOC_COSTLY_ORDER ||
1782
			 sc->priority < DEF_PRIORITY - 2))
M
Mel Gorman 已提交
1783 1784 1785 1786 1787
		return true;

	return false;
}

1788
/*
M
Mel Gorman 已提交
1789 1790 1791 1792 1793
 * 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.
1794
 */
1795
static inline bool should_continue_reclaim(struct lruvec *lruvec,
1796 1797 1798 1799 1800 1801 1802 1803
					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 */
1804
	if (!in_reclaim_compaction(sc))
1805 1806
		return false;

1807 1808 1809 1810 1811 1812 1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823 1824 1825 1826 1827 1828
	/* 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;
	}
1829 1830 1831 1832 1833 1834

	/*
	 * If we have not reclaimed enough pages for compaction and the
	 * inactive lists are large enough, continue reclaiming
	 */
	pages_for_compaction = (2UL << sc->order);
1835
	inactive_lru_pages = get_lru_size(lruvec, LRU_INACTIVE_FILE);
1836
	if (nr_swap_pages > 0)
1837
		inactive_lru_pages += get_lru_size(lruvec, LRU_INACTIVE_ANON);
1838 1839 1840 1841 1842
	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 */
1843
	switch (compaction_suitable(lruvec_zone(lruvec), sc->order)) {
1844 1845 1846 1847 1848 1849 1850 1851
	case COMPACT_PARTIAL:
	case COMPACT_CONTINUE:
		return false;
	default:
		return true;
	}
}

L
Linus Torvalds 已提交
1852 1853 1854
/*
 * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
 */
1855
static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
L
Linus Torvalds 已提交
1856
{
1857
	unsigned long nr[NR_LRU_LISTS];
1858
	unsigned long nr_to_scan;
H
Hugh Dickins 已提交
1859
	enum lru_list lru;
1860
	unsigned long nr_reclaimed, nr_scanned;
1861
	unsigned long nr_to_reclaim = sc->nr_to_reclaim;
1862
	struct blk_plug plug;
1863

1864 1865
restart:
	nr_reclaimed = 0;
1866
	nr_scanned = sc->nr_scanned;
1867
	get_scan_count(lruvec, sc, nr);
L
Linus Torvalds 已提交
1868

1869
	blk_start_plug(&plug);
1870 1871
	while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
					nr[LRU_INACTIVE_FILE]) {
H
Hugh Dickins 已提交
1872 1873
		for_each_evictable_lru(lru) {
			if (nr[lru]) {
K
KOSAKI Motohiro 已提交
1874
				nr_to_scan = min_t(unsigned long,
H
Hugh Dickins 已提交
1875 1876
						   nr[lru], SWAP_CLUSTER_MAX);
				nr[lru] -= nr_to_scan;
L
Linus Torvalds 已提交
1877

H
Hugh Dickins 已提交
1878
				nr_reclaimed += shrink_list(lru, nr_to_scan,
1879
							    lruvec, sc);
1880
			}
L
Linus Torvalds 已提交
1881
		}
1882 1883 1884 1885 1886 1887 1888 1889
		/*
		 * On large memory systems, scan >> priority can become
		 * really large. This is fine for the starting priority;
		 * we want to put equal scanning pressure on each zone.
		 * However, if the VM has a harder time of freeing pages,
		 * with multiple processes reclaiming pages, the total
		 * freeing target can get unreasonably large.
		 */
1890 1891
		if (nr_reclaimed >= nr_to_reclaim &&
		    sc->priority < DEF_PRIORITY)
1892
			break;
L
Linus Torvalds 已提交
1893
	}
1894
	blk_finish_plug(&plug);
1895
	sc->nr_reclaimed += nr_reclaimed;
1896

1897 1898 1899 1900
	/*
	 * Even if we did not try to evict anon pages at all, we want to
	 * rebalance the anon lru active/inactive ratio.
	 */
1901
	if (inactive_anon_is_low(lruvec))
1902
		shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
1903
				   sc, LRU_ACTIVE_ANON);
1904

1905
	/* reclaim/compaction might need reclaim to continue */
1906
	if (should_continue_reclaim(lruvec, nr_reclaimed,
1907
				    sc->nr_scanned - nr_scanned, sc))
1908 1909
		goto restart;

1910
	throttle_vm_writeout(sc->gfp_mask);
L
Linus Torvalds 已提交
1911 1912
}

1913
static void shrink_zone(struct zone *zone, struct scan_control *sc)
1914
{
1915 1916
	struct mem_cgroup *root = sc->target_mem_cgroup;
	struct mem_cgroup_reclaim_cookie reclaim = {
1917
		.zone = zone,
1918
		.priority = sc->priority,
1919
	};
1920 1921 1922 1923
	struct mem_cgroup *memcg;

	memcg = mem_cgroup_iter(root, NULL, &reclaim);
	do {
1924 1925 1926
		struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);

		shrink_lruvec(lruvec, sc);
1927

1928 1929 1930 1931 1932
		/*
		 * Limit reclaim has historically picked one memcg and
		 * scanned it with decreasing priority levels until
		 * nr_to_reclaim had been reclaimed.  This priority
		 * cycle is thus over after a single memcg.
1933 1934 1935 1936
		 *
		 * Direct reclaim and kswapd, on the other hand, have
		 * to scan all memory cgroups to fulfill the overall
		 * scan target for the zone.
1937 1938 1939 1940 1941 1942 1943
		 */
		if (!global_reclaim(sc)) {
			mem_cgroup_iter_break(root, memcg);
			break;
		}
		memcg = mem_cgroup_iter(root, memcg, &reclaim);
	} while (memcg);
1944 1945
}

1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971
/* 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),
		(zone->present_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
			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
	 */
1972
	if (compaction_deferred(zone, sc->order))
1973 1974 1975 1976 1977 1978 1979 1980 1981
		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
1982 1983 1984 1985 1986
/*
 * 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.
 *
1987 1988
 * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
 * Because:
L
Linus Torvalds 已提交
1989 1990
 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
 *    allocation or
1991 1992 1993
 * 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
1994 1995 1996
 *
 * If a zone is deemed to be full of pinned pages then just give it a light
 * scan then give up on it.
1997 1998
 *
 * This function returns true if a zone is being reclaimed for a costly
1999
 * high-order allocation and compaction is ready to begin. This indicates to
2000 2001
 * the caller that it should consider retrying the allocation instead of
 * further reclaim.
L
Linus Torvalds 已提交
2002
 */
2003
static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
L
Linus Torvalds 已提交
2004
{
2005
	struct zoneref *z;
2006
	struct zone *zone;
2007 2008
	unsigned long nr_soft_reclaimed;
	unsigned long nr_soft_scanned;
2009
	bool aborted_reclaim = false;
2010

2011 2012 2013 2014 2015 2016 2017 2018
	/*
	 * 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
	 */
	if (buffer_heads_over_limit)
		sc->gfp_mask |= __GFP_HIGHMEM;

2019 2020
	for_each_zone_zonelist_nodemask(zone, z, zonelist,
					gfp_zone(sc->gfp_mask), sc->nodemask) {
2021
		if (!populated_zone(zone))
L
Linus Torvalds 已提交
2022
			continue;
2023 2024 2025 2026
		/*
		 * Take care memory controller reclaiming has small influence
		 * to global LRU.
		 */
2027
		if (global_reclaim(sc)) {
2028 2029
			if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
				continue;
2030 2031
			if (zone->all_unreclaimable &&
					sc->priority != DEF_PRIORITY)
2032
				continue;	/* Let kswapd poll it */
2033
			if (IS_ENABLED(CONFIG_COMPACTION)) {
2034
				/*
2035 2036 2037 2038 2039
				 * 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
2040 2041
				 * noticeable problem, like transparent huge
				 * page allocations.
2042
				 */
2043
				if (compaction_ready(zone, sc)) {
2044
					aborted_reclaim = true;
2045
					continue;
2046
				}
2047
			}
2048 2049 2050 2051 2052 2053 2054 2055 2056 2057 2058 2059 2060
			/*
			 * This steals pages from memory cgroups over softlimit
			 * and returns the number of reclaimed pages and
			 * scanned pages. This works for global memory pressure
			 * and balancing, not for a memcg's limit.
			 */
			nr_soft_scanned = 0;
			nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
						sc->order, sc->gfp_mask,
						&nr_soft_scanned);
			sc->nr_reclaimed += nr_soft_reclaimed;
			sc->nr_scanned += nr_soft_scanned;
			/* need some check for avoid more shrink_zone() */
2061
		}
2062

2063
		shrink_zone(zone, sc);
L
Linus Torvalds 已提交
2064
	}
2065

2066
	return aborted_reclaim;
2067 2068 2069 2070 2071 2072 2073
}

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

2074
/* All zones in zonelist are unreclaimable? */
2075 2076 2077 2078 2079 2080 2081 2082 2083 2084 2085 2086
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;
2087 2088
		if (!zone->all_unreclaimable)
			return false;
2089 2090
	}

2091
	return true;
L
Linus Torvalds 已提交
2092
}
2093

L
Linus Torvalds 已提交
2094 2095 2096 2097 2098 2099 2100 2101
/*
 * 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
2102 2103 2104 2105
 * 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.
2106 2107 2108
 *
 * returns:	0, if no pages reclaimed
 * 		else, the number of pages reclaimed
L
Linus Torvalds 已提交
2109
 */
2110
static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2111 2112
					struct scan_control *sc,
					struct shrink_control *shrink)
L
Linus Torvalds 已提交
2113
{
2114
	unsigned long total_scanned = 0;
L
Linus Torvalds 已提交
2115
	struct reclaim_state *reclaim_state = current->reclaim_state;
2116
	struct zoneref *z;
2117
	struct zone *zone;
2118
	unsigned long writeback_threshold;
2119
	bool aborted_reclaim;
L
Linus Torvalds 已提交
2120

2121 2122
	delayacct_freepages_start();

2123
	if (global_reclaim(sc))
2124
		count_vm_event(ALLOCSTALL);
L
Linus Torvalds 已提交
2125

2126
	do {
2127
		sc->nr_scanned = 0;
2128
		aborted_reclaim = shrink_zones(zonelist, sc);
2129

2130 2131 2132 2133
		/*
		 * Don't shrink slabs when reclaiming memory from
		 * over limit cgroups
		 */
2134
		if (global_reclaim(sc)) {
2135
			unsigned long lru_pages = 0;
2136 2137
			for_each_zone_zonelist(zone, z, zonelist,
					gfp_zone(sc->gfp_mask)) {
2138 2139 2140 2141 2142 2143
				if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
					continue;

				lru_pages += zone_reclaimable_pages(zone);
			}

2144
			shrink_slab(shrink, sc->nr_scanned, lru_pages);
2145
			if (reclaim_state) {
2146
				sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2147 2148
				reclaim_state->reclaimed_slab = 0;
			}
L
Linus Torvalds 已提交
2149
		}
2150
		total_scanned += sc->nr_scanned;
2151
		if (sc->nr_reclaimed >= sc->nr_to_reclaim)
L
Linus Torvalds 已提交
2152 2153 2154 2155 2156 2157 2158 2159 2160
			goto out;

		/*
		 * 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.
		 */
2161 2162
		writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
		if (total_scanned > writeback_threshold) {
2163 2164
			wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
						WB_REASON_TRY_TO_FREE_PAGES);
2165
			sc->may_writepage = 1;
L
Linus Torvalds 已提交
2166 2167 2168
		}

		/* Take a nap, wait for some writeback to complete */
2169
		if (!sc->hibernation_mode && sc->nr_scanned &&
2170
		    sc->priority < DEF_PRIORITY - 2) {
2171 2172 2173
			struct zone *preferred_zone;

			first_zones_zonelist(zonelist, gfp_zone(sc->gfp_mask),
2174 2175
						&cpuset_current_mems_allowed,
						&preferred_zone);
2176 2177
			wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/10);
		}
2178
	} while (--sc->priority >= 0);
2179

L
Linus Torvalds 已提交
2180
out:
2181 2182
	delayacct_freepages_end();

2183 2184 2185
	if (sc->nr_reclaimed)
		return sc->nr_reclaimed;

2186 2187 2188 2189 2190 2191 2192 2193
	/*
	 * 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;

2194 2195
	/* Aborted reclaim to try compaction? don't OOM, then */
	if (aborted_reclaim)
2196 2197
		return 1;

2198
	/* top priority shrink_zones still had more to do? don't OOM, then */
2199
	if (global_reclaim(sc) && !all_unreclaimable(zonelist, sc))
2200 2201 2202
		return 1;

	return 0;
L
Linus Torvalds 已提交
2203 2204
}

2205 2206 2207 2208 2209 2210 2211 2212 2213 2214 2215 2216 2217 2218 2219 2220 2221 2222 2223 2224 2225 2226 2227 2228 2229 2230 2231 2232 2233 2234
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];
		pfmemalloc_reserve += min_wmark_pages(zone);
		free_pages += zone_page_state(zone, NR_FREE_PAGES);
	}

	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
2235 2236 2237 2238
 * 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.
2239
 */
2240
static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
2241 2242 2243 2244 2245 2246 2247 2248 2249 2250 2251 2252 2253 2254
					nodemask_t *nodemask)
{
	struct zone *zone;
	int high_zoneidx = gfp_zone(gfp_mask);
	pg_data_t *pgdat;

	/*
	 * 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)
2255 2256 2257 2258 2259 2260 2261 2262
		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;
2263 2264 2265 2266 2267

	/* Check if the pfmemalloc reserves are ok */
	first_zones_zonelist(zonelist, high_zoneidx, NULL, &zone);
	pgdat = zone->zone_pgdat;
	if (pfmemalloc_watermark_ok(pgdat))
2268
		goto out;
2269

2270 2271 2272
	/* Account for the throttling */
	count_vm_event(PGSCAN_DIRECT_THROTTLE);

2273 2274 2275 2276 2277 2278 2279 2280 2281 2282 2283
	/*
	 * 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);
2284 2285

		goto check_pending;
2286 2287 2288 2289 2290
	}

	/* Throttle until kswapd wakes the process */
	wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
		pfmemalloc_watermark_ok(pgdat));
2291 2292 2293 2294 2295 2296 2297

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

out:
	return false;
2298 2299
}

2300
unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2301
				gfp_t gfp_mask, nodemask_t *nodemask)
2302
{
2303
	unsigned long nr_reclaimed;
2304 2305 2306
	struct scan_control sc = {
		.gfp_mask = gfp_mask,
		.may_writepage = !laptop_mode,
2307
		.nr_to_reclaim = SWAP_CLUSTER_MAX,
2308
		.may_unmap = 1,
2309
		.may_swap = 1,
2310
		.order = order,
2311
		.priority = DEF_PRIORITY,
2312
		.target_mem_cgroup = NULL,
2313
		.nodemask = nodemask,
2314
	};
2315 2316 2317
	struct shrink_control shrink = {
		.gfp_mask = sc.gfp_mask,
	};
2318

2319
	/*
2320 2321 2322
	 * 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.
2323
	 */
2324
	if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask))
2325 2326
		return 1;

2327 2328 2329 2330
	trace_mm_vmscan_direct_reclaim_begin(order,
				sc.may_writepage,
				gfp_mask);

2331
	nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2332 2333 2334 2335

	trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);

	return nr_reclaimed;
2336 2337
}

A
Andrew Morton 已提交
2338
#ifdef CONFIG_MEMCG
2339

2340
unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
2341
						gfp_t gfp_mask, bool noswap,
2342 2343
						struct zone *zone,
						unsigned long *nr_scanned)
2344 2345
{
	struct scan_control sc = {
2346
		.nr_scanned = 0,
2347
		.nr_to_reclaim = SWAP_CLUSTER_MAX,
2348 2349 2350 2351
		.may_writepage = !laptop_mode,
		.may_unmap = 1,
		.may_swap = !noswap,
		.order = 0,
2352
		.priority = 0,
2353
		.target_mem_cgroup = memcg,
2354
	};
2355
	struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2356

2357 2358
	sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
			(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2359

2360
	trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
2361 2362 2363
						      sc.may_writepage,
						      sc.gfp_mask);

2364 2365 2366 2367 2368 2369 2370
	/*
	 * 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.
	 */
2371
	shrink_lruvec(lruvec, &sc);
2372 2373 2374

	trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);

2375
	*nr_scanned = sc.nr_scanned;
2376 2377 2378
	return sc.nr_reclaimed;
}

2379
unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
K
KOSAKI Motohiro 已提交
2380
					   gfp_t gfp_mask,
2381
					   bool noswap)
2382
{
2383
	struct zonelist *zonelist;
2384
	unsigned long nr_reclaimed;
2385
	int nid;
2386 2387
	struct scan_control sc = {
		.may_writepage = !laptop_mode,
2388
		.may_unmap = 1,
2389
		.may_swap = !noswap,
2390
		.nr_to_reclaim = SWAP_CLUSTER_MAX,
2391
		.order = 0,
2392
		.priority = DEF_PRIORITY,
2393
		.target_mem_cgroup = memcg,
2394
		.nodemask = NULL, /* we don't care the placement */
2395 2396 2397 2398 2399
		.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
				(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
	};
	struct shrink_control shrink = {
		.gfp_mask = sc.gfp_mask,
2400 2401
	};

2402 2403 2404 2405 2406
	/*
	 * 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.
	 */
2407
	nid = mem_cgroup_select_victim_node(memcg);
2408 2409

	zonelist = NODE_DATA(nid)->node_zonelists;
2410 2411 2412 2413 2414

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

2415
	nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2416 2417 2418 2419

	trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);

	return nr_reclaimed;
2420 2421 2422
}
#endif

2423
static void age_active_anon(struct zone *zone, struct scan_control *sc)
2424
{
2425
	struct mem_cgroup *memcg;
2426

2427 2428 2429 2430 2431
	if (!total_swap_pages)
		return;

	memcg = mem_cgroup_iter(NULL, NULL, NULL);
	do {
2432
		struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2433

2434
		if (inactive_anon_is_low(lruvec))
2435
			shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2436
					   sc, LRU_ACTIVE_ANON);
2437 2438 2439

		memcg = mem_cgroup_iter(NULL, memcg, NULL);
	} while (memcg);
2440 2441
}

2442 2443 2444 2445 2446 2447 2448
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;

2449 2450
	if (IS_ENABLED(CONFIG_COMPACTION) && order &&
	    !compaction_suitable(zone, order))
2451 2452 2453 2454 2455
		return false;

	return true;
}

2456
/*
2457 2458 2459 2460 2461 2462 2463 2464 2465 2466
 * 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.
2467 2468 2469 2470
 * 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
2471
 *     percentage of the middle zones. For example, on 32-bit x86, highmem
2472 2473 2474 2475
 *     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.
 */
2476
static bool pgdat_balanced(pg_data_t *pgdat, int order, int classzone_idx)
2477 2478
{
	unsigned long present_pages = 0;
2479
	unsigned long balanced_pages = 0;
2480 2481
	int i;

2482 2483 2484
	/* Check the watermark levels */
	for (i = 0; i <= classzone_idx; i++) {
		struct zone *zone = pgdat->node_zones + i;
2485

2486 2487 2488 2489 2490 2491 2492 2493 2494 2495 2496 2497 2498 2499 2500 2501 2502 2503 2504 2505 2506 2507 2508 2509 2510 2511 2512
		if (!populated_zone(zone))
			continue;

		present_pages += zone->present_pages;

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

		if (zone_balanced(zone, order, 0, i))
			balanced_pages += zone->present_pages;
		else if (!order)
			return false;
	}

	if (order)
		return balanced_pages >= (present_pages >> 2);
	else
		return true;
2513 2514
}

2515 2516 2517 2518 2519 2520 2521
/*
 * 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,
2522
					int classzone_idx)
2523 2524 2525
{
	/* If a direct reclaimer woke kswapd within HZ/10, it's premature */
	if (remaining)
2526 2527 2528 2529 2530 2531 2532 2533 2534 2535 2536 2537 2538 2539 2540
		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;
	}
2541

2542
	return pgdat_balanced(pgdat, order, classzone_idx);
2543 2544
}

L
Linus Torvalds 已提交
2545 2546
/*
 * For kswapd, balance_pgdat() will work across all this node's zones until
2547
 * they are all at high_wmark_pages(zone).
L
Linus Torvalds 已提交
2548
 *
2549
 * Returns the final order kswapd was reclaiming at
L
Linus Torvalds 已提交
2550 2551 2552 2553 2554 2555 2556 2557 2558 2559
 *
 * 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
2560 2561 2562 2563 2564
 * 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
2565
 */
2566
static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
2567
							int *classzone_idx)
L
Linus Torvalds 已提交
2568
{
2569
	struct zone *unbalanced_zone;
L
Linus Torvalds 已提交
2570
	int i;
2571
	int end_zone = 0;	/* Inclusive.  0 = ZONE_DMA */
2572
	unsigned long total_scanned;
L
Linus Torvalds 已提交
2573
	struct reclaim_state *reclaim_state = current->reclaim_state;
2574 2575
	unsigned long nr_soft_reclaimed;
	unsigned long nr_soft_scanned;
2576 2577
	struct scan_control sc = {
		.gfp_mask = GFP_KERNEL,
2578
		.may_unmap = 1,
2579
		.may_swap = 1,
2580 2581 2582 2583 2584
		/*
		 * kswapd doesn't want to be bailed out while reclaim. because
		 * we want to put equal scanning pressure on each zone.
		 */
		.nr_to_reclaim = ULONG_MAX,
A
Andy Whitcroft 已提交
2585
		.order = order,
2586
		.target_mem_cgroup = NULL,
2587
	};
2588 2589 2590
	struct shrink_control shrink = {
		.gfp_mask = sc.gfp_mask,
	};
L
Linus Torvalds 已提交
2591 2592
loop_again:
	total_scanned = 0;
2593
	sc.priority = DEF_PRIORITY;
2594
	sc.nr_reclaimed = 0;
C
Christoph Lameter 已提交
2595
	sc.may_writepage = !laptop_mode;
2596
	count_vm_event(PAGEOUTRUN);
L
Linus Torvalds 已提交
2597

2598
	do {
L
Linus Torvalds 已提交
2599
		unsigned long lru_pages = 0;
2600
		int has_under_min_watermark_zone = 0;
L
Linus Torvalds 已提交
2601

2602
		unbalanced_zone = NULL;
L
Linus Torvalds 已提交
2603

2604 2605 2606 2607 2608 2609
		/*
		 * 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
2610

2611 2612
			if (!populated_zone(zone))
				continue;
L
Linus Torvalds 已提交
2613

2614 2615
			if (zone->all_unreclaimable &&
			    sc.priority != DEF_PRIORITY)
2616
				continue;
L
Linus Torvalds 已提交
2617

2618 2619 2620 2621
			/*
			 * Do some background aging of the anon list, to give
			 * pages a chance to be referenced before reclaiming.
			 */
2622
			age_active_anon(zone, &sc);
2623

2624 2625 2626 2627 2628 2629 2630 2631 2632 2633 2634
			/*
			 * 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;
			}

2635
			if (!zone_balanced(zone, order, 0, 0)) {
2636
				end_zone = i;
A
Andrew Morton 已提交
2637
				break;
2638 2639 2640
			} else {
				/* If balanced, clear the congested flag */
				zone_clear_flag(zone, ZONE_CONGESTED);
L
Linus Torvalds 已提交
2641 2642
			}
		}
A
Andrew Morton 已提交
2643 2644 2645
		if (i < 0)
			goto out;

L
Linus Torvalds 已提交
2646 2647 2648
		for (i = 0; i <= end_zone; i++) {
			struct zone *zone = pgdat->node_zones + i;

2649
			lru_pages += zone_reclaimable_pages(zone);
L
Linus Torvalds 已提交
2650 2651 2652 2653 2654 2655 2656 2657 2658 2659 2660 2661 2662
		}

		/*
		 * 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;
2663
			int nr_slab, testorder;
2664
			unsigned long balance_gap;
L
Linus Torvalds 已提交
2665

2666
			if (!populated_zone(zone))
L
Linus Torvalds 已提交
2667 2668
				continue;

2669 2670
			if (zone->all_unreclaimable &&
			    sc.priority != DEF_PRIORITY)
L
Linus Torvalds 已提交
2671 2672 2673
				continue;

			sc.nr_scanned = 0;
2674

2675
			nr_soft_scanned = 0;
2676 2677 2678
			/*
			 * Call soft limit reclaim before calling shrink_zone.
			 */
2679 2680 2681 2682 2683
			nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
							order, sc.gfp_mask,
							&nr_soft_scanned);
			sc.nr_reclaimed += nr_soft_reclaimed;
			total_scanned += nr_soft_scanned;
2684

2685
			/*
2686 2687 2688 2689 2690 2691
			 * 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.
2692
			 */
2693 2694 2695 2696
			balance_gap = min(low_wmark_pages(zone),
				(zone->present_pages +
					KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
				KSWAPD_ZONE_BALANCE_GAP_RATIO);
2697 2698 2699 2700 2701 2702 2703 2704
			/*
			 * 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.
			 */
			testorder = order;
2705
			if (IS_ENABLED(CONFIG_COMPACTION) && order &&
2706 2707 2708 2709
					compaction_suitable(zone, order) !=
						COMPACT_SKIPPED)
				testorder = 0;

2710
			if ((buffer_heads_over_limit && is_highmem_idx(i)) ||
2711 2712
			    !zone_balanced(zone, testorder,
					   balance_gap, end_zone)) {
2713
				shrink_zone(zone, &sc);
2714

2715 2716 2717 2718 2719 2720 2721 2722 2723
				reclaim_state->reclaimed_slab = 0;
				nr_slab = shrink_slab(&shrink, sc.nr_scanned, lru_pages);
				sc.nr_reclaimed += reclaim_state->reclaimed_slab;
				total_scanned += sc.nr_scanned;

				if (nr_slab == 0 && !zone_reclaimable(zone))
					zone->all_unreclaimable = 1;
			}

L
Linus Torvalds 已提交
2724 2725 2726 2727 2728 2729
			/*
			 * If we've done a decent amount of scanning and
			 * the reclaim ratio is low, start doing writepage
			 * even in laptop mode
			 */
			if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
2730
			    total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
L
Linus Torvalds 已提交
2731
				sc.may_writepage = 1;
2732

2733 2734 2735
			if (zone->all_unreclaimable) {
				if (end_zone && end_zone == i)
					end_zone--;
2736
				continue;
2737
			}
2738

2739
			if (!zone_balanced(zone, testorder, 0, end_zone)) {
2740
				unbalanced_zone = zone;
2741 2742 2743 2744 2745
				/*
				 * We are still under min water mark.  This
				 * means that we have a GFP_ATOMIC allocation
				 * failure risk. Hurry up!
				 */
2746
				if (!zone_watermark_ok_safe(zone, order,
2747 2748
					    min_wmark_pages(zone), end_zone, 0))
					has_under_min_watermark_zone = 1;
2749 2750 2751 2752 2753 2754
			} else {
				/*
				 * 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,
2755
				 * speculatively avoid congestion waits
2756 2757
				 */
				zone_clear_flag(zone, ZONE_CONGESTED);
2758
			}
2759

L
Linus Torvalds 已提交
2760
		}
2761 2762 2763 2764 2765 2766 2767 2768 2769 2770

		/*
		 * 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);

2771
		if (pgdat_balanced(pgdat, order, *classzone_idx))
L
Linus Torvalds 已提交
2772 2773 2774 2775 2776
			break;		/* kswapd: all done */
		/*
		 * OK, kswapd is getting into trouble.  Take a nap, then take
		 * another pass across the zones.
		 */
2777
		if (total_scanned && (sc.priority < DEF_PRIORITY - 2)) {
2778 2779
			if (has_under_min_watermark_zone)
				count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
2780
			else if (unbalanced_zone)
2781
				wait_iff_congested(unbalanced_zone, BLK_RW_ASYNC, HZ/10);
2782
		}
L
Linus Torvalds 已提交
2783 2784 2785 2786 2787 2788 2789

		/*
		 * We do this so kswapd doesn't build up large priorities for
		 * example when it is freeing in parallel with allocators. It
		 * matches the direct reclaim path behaviour in terms of impact
		 * on zone->*_priority.
		 */
2790
		if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
L
Linus Torvalds 已提交
2791
			break;
2792
	} while (--sc.priority >= 0);
L
Linus Torvalds 已提交
2793
out:
2794

2795
	if (!pgdat_balanced(pgdat, order, *classzone_idx)) {
L
Linus Torvalds 已提交
2796
		cond_resched();
2797 2798 2799

		try_to_freeze();

2800 2801 2802 2803 2804 2805 2806 2807 2808 2809 2810 2811 2812 2813 2814 2815 2816
		/*
		 * Fragmentation may mean that the system cannot be
		 * rebalanced for high-order allocations in all zones.
		 * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX,
		 * it means the zones have been fully scanned and are still
		 * not balanced. For high-order allocations, there is
		 * little point trying all over again as kswapd may
		 * infinite loop.
		 *
		 * Instead, recheck all watermarks at order-0 as they
		 * are the most important. If watermarks are ok, kswapd will go
		 * back to sleep. High-order users can still perform direct
		 * reclaim if they wish.
		 */
		if (sc.nr_reclaimed < SWAP_CLUSTER_MAX)
			order = sc.order = 0;

L
Linus Torvalds 已提交
2817 2818 2819
		goto loop_again;
	}

2820 2821 2822 2823 2824 2825 2826 2827 2828
	/*
	 * If kswapd was reclaiming at a higher order, it has the option of
	 * sleeping without all zones being balanced. Before it does, it must
	 * ensure that the watermarks for order-0 on *all* zones are met and
	 * that the congestion flags are cleared. The congestion flag must
	 * be cleared as kswapd is the only mechanism that clears the flag
	 * and it is potentially going to sleep here.
	 */
	if (order) {
2829 2830
		int zones_need_compaction = 1;

2831 2832 2833 2834 2835 2836
		for (i = 0; i <= end_zone; i++) {
			struct zone *zone = pgdat->node_zones + i;

			if (!populated_zone(zone))
				continue;

2837 2838 2839 2840
			/* Check if the memory needs to be defragmented. */
			if (zone_watermark_ok(zone, order,
				    low_wmark_pages(zone), *classzone_idx, 0))
				zones_need_compaction = 0;
2841
		}
2842 2843 2844

		if (zones_need_compaction)
			compact_pgdat(pgdat, order);
2845 2846
	}

2847
	/*
2848
	 * Return the order we were reclaiming at so prepare_kswapd_sleep()
2849 2850 2851 2852
	 * 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
	 */
2853
	*classzone_idx = end_zone;
2854
	return order;
L
Linus Torvalds 已提交
2855 2856
}

2857
static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
2858 2859 2860 2861 2862 2863 2864 2865 2866 2867
{
	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 */
2868
	if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
2869 2870 2871 2872 2873 2874 2875 2876 2877
		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.
	 */
2878
	if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
2879 2880 2881 2882 2883 2884 2885 2886 2887 2888 2889
		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);
2890

2891 2892 2893 2894 2895 2896 2897 2898
		/*
		 * 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);

2899 2900 2901
		if (!kthread_should_stop())
			schedule();

2902 2903 2904 2905 2906 2907 2908 2909 2910 2911
		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
2912 2913
/*
 * The background pageout daemon, started as a kernel thread
2914
 * from the init process.
L
Linus Torvalds 已提交
2915 2916 2917 2918 2919 2920 2921 2922 2923 2924 2925 2926
 *
 * 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)
{
2927
	unsigned long order, new_order;
2928
	unsigned balanced_order;
2929
	int classzone_idx, new_classzone_idx;
2930
	int balanced_classzone_idx;
L
Linus Torvalds 已提交
2931 2932
	pg_data_t *pgdat = (pg_data_t*)p;
	struct task_struct *tsk = current;
2933

L
Linus Torvalds 已提交
2934 2935 2936
	struct reclaim_state reclaim_state = {
		.reclaimed_slab = 0,
	};
2937
	const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
L
Linus Torvalds 已提交
2938

2939 2940
	lockdep_set_current_reclaim_state(GFP_KERNEL);

R
Rusty Russell 已提交
2941
	if (!cpumask_empty(cpumask))
2942
		set_cpus_allowed_ptr(tsk, cpumask);
L
Linus Torvalds 已提交
2943 2944 2945 2946 2947 2948 2949 2950 2951 2952 2953 2954 2955 2956
	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).
	 */
2957
	tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
2958
	set_freezable();
L
Linus Torvalds 已提交
2959

2960
	order = new_order = 0;
2961
	balanced_order = 0;
2962
	classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
2963
	balanced_classzone_idx = classzone_idx;
L
Linus Torvalds 已提交
2964
	for ( ; ; ) {
2965
		bool ret;
2966

2967 2968 2969 2970 2971
		/*
		 * 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
		 */
2972 2973
		if (balanced_classzone_idx >= new_classzone_idx &&
					balanced_order == new_order) {
2974 2975 2976 2977 2978 2979
			new_order = pgdat->kswapd_max_order;
			new_classzone_idx = pgdat->classzone_idx;
			pgdat->kswapd_max_order =  0;
			pgdat->classzone_idx = pgdat->nr_zones - 1;
		}

2980
		if (order < new_order || classzone_idx > new_classzone_idx) {
L
Linus Torvalds 已提交
2981 2982
			/*
			 * Don't sleep if someone wants a larger 'order'
2983
			 * allocation or has tigher zone constraints
L
Linus Torvalds 已提交
2984 2985
			 */
			order = new_order;
2986
			classzone_idx = new_classzone_idx;
L
Linus Torvalds 已提交
2987
		} else {
2988 2989
			kswapd_try_to_sleep(pgdat, balanced_order,
						balanced_classzone_idx);
L
Linus Torvalds 已提交
2990
			order = pgdat->kswapd_max_order;
2991
			classzone_idx = pgdat->classzone_idx;
2992 2993
			new_order = order;
			new_classzone_idx = classzone_idx;
2994
			pgdat->kswapd_max_order = 0;
2995
			pgdat->classzone_idx = pgdat->nr_zones - 1;
L
Linus Torvalds 已提交
2996 2997
		}

2998 2999 3000 3001 3002 3003 3004 3005
		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
		 */
3006 3007
		if (!ret) {
			trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
3008 3009 3010
			balanced_classzone_idx = classzone_idx;
			balanced_order = balance_pgdat(pgdat, order,
						&balanced_classzone_idx);
3011
		}
L
Linus Torvalds 已提交
3012
	}
3013 3014

	current->reclaim_state = NULL;
L
Linus Torvalds 已提交
3015 3016 3017 3018 3019 3020
	return 0;
}

/*
 * A zone is low on free memory, so wake its kswapd task to service it.
 */
3021
void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
L
Linus Torvalds 已提交
3022 3023 3024
{
	pg_data_t *pgdat;

3025
	if (!populated_zone(zone))
L
Linus Torvalds 已提交
3026 3027
		return;

3028
	if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
L
Linus Torvalds 已提交
3029
		return;
3030
	pgdat = zone->zone_pgdat;
3031
	if (pgdat->kswapd_max_order < order) {
L
Linus Torvalds 已提交
3032
		pgdat->kswapd_max_order = order;
3033 3034
		pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
	}
3035
	if (!waitqueue_active(&pgdat->kswapd_wait))
L
Linus Torvalds 已提交
3036
		return;
3037 3038 3039 3040
	if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0))
		return;

	trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
3041
	wake_up_interruptible(&pgdat->kswapd_wait);
L
Linus Torvalds 已提交
3042 3043
}

3044 3045 3046 3047 3048 3049 3050 3051
/*
 * The reclaimable count would be mostly accurate.
 * The less reclaimable pages may be
 * - mlocked pages, which will be moved to unevictable list when encountered
 * - mapped pages, which may require several travels to be reclaimed
 * - dirty pages, which is not "instantly" reclaimable
 */
unsigned long global_reclaimable_pages(void)
3052
{
3053 3054 3055 3056 3057 3058 3059 3060 3061 3062 3063 3064 3065 3066 3067 3068 3069 3070 3071 3072 3073 3074 3075 3076
	int nr;

	nr = global_page_state(NR_ACTIVE_FILE) +
	     global_page_state(NR_INACTIVE_FILE);

	if (nr_swap_pages > 0)
		nr += global_page_state(NR_ACTIVE_ANON) +
		      global_page_state(NR_INACTIVE_ANON);

	return nr;
}

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

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

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

	return nr;
3077 3078
}

3079
#ifdef CONFIG_HIBERNATION
L
Linus Torvalds 已提交
3080
/*
3081
 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
3082 3083 3084 3085 3086
 * 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
3087
 */
3088
unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
L
Linus Torvalds 已提交
3089
{
3090 3091
	struct reclaim_state reclaim_state;
	struct scan_control sc = {
3092 3093 3094
		.gfp_mask = GFP_HIGHUSER_MOVABLE,
		.may_swap = 1,
		.may_unmap = 1,
3095
		.may_writepage = 1,
3096 3097 3098
		.nr_to_reclaim = nr_to_reclaim,
		.hibernation_mode = 1,
		.order = 0,
3099
		.priority = DEF_PRIORITY,
L
Linus Torvalds 已提交
3100
	};
3101 3102 3103 3104
	struct shrink_control shrink = {
		.gfp_mask = sc.gfp_mask,
	};
	struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3105 3106
	struct task_struct *p = current;
	unsigned long nr_reclaimed;
L
Linus Torvalds 已提交
3107

3108 3109 3110 3111
	p->flags |= PF_MEMALLOC;
	lockdep_set_current_reclaim_state(sc.gfp_mask);
	reclaim_state.reclaimed_slab = 0;
	p->reclaim_state = &reclaim_state;
3112

3113
	nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
3114

3115 3116 3117
	p->reclaim_state = NULL;
	lockdep_clear_current_reclaim_state();
	p->flags &= ~PF_MEMALLOC;
3118

3119
	return nr_reclaimed;
L
Linus Torvalds 已提交
3120
}
3121
#endif /* CONFIG_HIBERNATION */
L
Linus Torvalds 已提交
3122 3123 3124 3125 3126

/* 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. */
3127 3128
static int cpu_callback(struct notifier_block *nfb, unsigned long action,
			void *hcpu)
L
Linus Torvalds 已提交
3129
{
3130
	int nid;
L
Linus Torvalds 已提交
3131

3132
	if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
3133
		for_each_node_state(nid, N_MEMORY) {
3134
			pg_data_t *pgdat = NODE_DATA(nid);
3135 3136 3137
			const struct cpumask *mask;

			mask = cpumask_of_node(pgdat->node_id);
3138

3139
			if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
L
Linus Torvalds 已提交
3140
				/* One of our CPUs online: restore mask */
3141
				set_cpus_allowed_ptr(pgdat->kswapd, mask);
L
Linus Torvalds 已提交
3142 3143 3144 3145 3146
		}
	}
	return NOTIFY_OK;
}

3147 3148 3149 3150 3151 3152 3153 3154 3155 3156 3157 3158 3159 3160 3161 3162
/*
 * 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);
3163
		pgdat->kswapd = NULL;
3164 3165
		pr_err("Failed to start kswapd on node %d\n", nid);
		ret = PTR_ERR(pgdat->kswapd);
3166 3167 3168 3169
	}
	return ret;
}

3170
/*
3171 3172
 * Called by memory hotplug when all memory in a node is offlined.  Caller must
 * hold lock_memory_hotplug().
3173 3174 3175 3176 3177
 */
void kswapd_stop(int nid)
{
	struct task_struct *kswapd = NODE_DATA(nid)->kswapd;

3178
	if (kswapd) {
3179
		kthread_stop(kswapd);
3180 3181
		NODE_DATA(nid)->kswapd = NULL;
	}
3182 3183
}

L
Linus Torvalds 已提交
3184 3185
static int __init kswapd_init(void)
{
3186
	int nid;
3187

L
Linus Torvalds 已提交
3188
	swap_setup();
3189
	for_each_node_state(nid, N_MEMORY)
3190
 		kswapd_run(nid);
L
Linus Torvalds 已提交
3191 3192 3193 3194 3195
	hotcpu_notifier(cpu_callback, 0);
	return 0;
}

module_init(kswapd_init)
3196 3197 3198 3199 3200 3201 3202 3203 3204 3205

#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;

3206
#define RECLAIM_OFF 0
3207
#define RECLAIM_ZONE (1<<0)	/* Run shrink_inactive_list on the zone */
3208 3209 3210
#define RECLAIM_WRITE (1<<1)	/* Writeout pages during reclaim */
#define RECLAIM_SWAP (1<<2)	/* Swap pages out during reclaim */

3211 3212 3213 3214 3215 3216 3217
/*
 * 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

3218 3219 3220 3221 3222 3223
/*
 * Percentage of pages in a zone that must be unmapped for zone_reclaim to
 * occur.
 */
int sysctl_min_unmapped_ratio = 1;

3224 3225 3226 3227 3228 3229
/*
 * 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;

3230 3231 3232 3233 3234 3235 3236 3237 3238 3239 3240 3241 3242 3243 3244 3245 3246 3247 3248 3249 3250 3251 3252 3253 3254 3255 3256 3257 3258 3259 3260 3261 3262 3263 3264 3265 3266 3267 3268 3269 3270 3271
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;
}

3272 3273 3274
/*
 * Try to free up some pages from this zone through reclaim.
 */
3275
static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3276
{
3277
	/* Minimum pages needed in order to stay on node */
3278
	const unsigned long nr_pages = 1 << order;
3279 3280
	struct task_struct *p = current;
	struct reclaim_state reclaim_state;
3281 3282
	struct scan_control sc = {
		.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
3283
		.may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
3284
		.may_swap = 1,
3285 3286
		.nr_to_reclaim = max_t(unsigned long, nr_pages,
				       SWAP_CLUSTER_MAX),
3287
		.gfp_mask = gfp_mask,
3288
		.order = order,
3289
		.priority = ZONE_RECLAIM_PRIORITY,
3290
	};
3291 3292 3293
	struct shrink_control shrink = {
		.gfp_mask = sc.gfp_mask,
	};
3294
	unsigned long nr_slab_pages0, nr_slab_pages1;
3295 3296

	cond_resched();
3297 3298 3299 3300 3301 3302
	/*
	 * 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;
3303
	lockdep_set_current_reclaim_state(gfp_mask);
3304 3305
	reclaim_state.reclaimed_slab = 0;
	p->reclaim_state = &reclaim_state;
3306

3307
	if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
3308 3309 3310 3311 3312
		/*
		 * Free memory by calling shrink zone with increasing
		 * priorities until we have enough memory freed.
		 */
		do {
3313 3314
			shrink_zone(zone, &sc);
		} while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
3315
	}
3316

3317 3318
	nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
	if (nr_slab_pages0 > zone->min_slab_pages) {
3319
		/*
3320
		 * shrink_slab() does not currently allow us to determine how
3321 3322 3323 3324
		 * 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.
3325
		 *
3326 3327
		 * Note that shrink_slab will free memory on all zones and may
		 * take a long time.
3328
		 */
3329 3330 3331 3332
		for (;;) {
			unsigned long lru_pages = zone_reclaimable_pages(zone);

			/* No reclaimable slab or very low memory pressure */
3333
			if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages))
3334 3335 3336 3337 3338 3339 3340 3341
				break;

			/* Freed enough memory */
			nr_slab_pages1 = zone_page_state(zone,
							NR_SLAB_RECLAIMABLE);
			if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
				break;
		}
3342 3343 3344 3345 3346

		/*
		 * Update nr_reclaimed by the number of slab pages we
		 * reclaimed from this zone.
		 */
3347 3348 3349
		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;
3350 3351
	}

3352
	p->reclaim_state = NULL;
3353
	current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
3354
	lockdep_clear_current_reclaim_state();
3355
	return sc.nr_reclaimed >= nr_pages;
3356
}
3357 3358 3359 3360

int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
{
	int node_id;
3361
	int ret;
3362 3363

	/*
3364 3365
	 * Zone reclaim reclaims unmapped file backed pages and
	 * slab pages if we are over the defined limits.
3366
	 *
3367 3368 3369 3370 3371
	 * 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.
3372
	 */
3373 3374
	if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
	    zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
3375
		return ZONE_RECLAIM_FULL;
3376

3377
	if (zone->all_unreclaimable)
3378
		return ZONE_RECLAIM_FULL;
3379

3380
	/*
3381
	 * Do not scan if the allocation should not be delayed.
3382
	 */
3383
	if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
3384
		return ZONE_RECLAIM_NOSCAN;
3385 3386 3387 3388 3389 3390 3391

	/*
	 * 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.
	 */
3392
	node_id = zone_to_nid(zone);
3393
	if (node_state(node_id, N_CPU) && node_id != numa_node_id())
3394
		return ZONE_RECLAIM_NOSCAN;
3395 3396

	if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
3397 3398
		return ZONE_RECLAIM_NOSCAN;

3399 3400 3401
	ret = __zone_reclaim(zone, gfp_mask, order);
	zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);

3402 3403 3404
	if (!ret)
		count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);

3405
	return ret;
3406
}
3407
#endif
L
Lee Schermerhorn 已提交
3408 3409 3410 3411 3412 3413

/*
 * 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
3414
 * lists vs unevictable list.
L
Lee Schermerhorn 已提交
3415 3416
 *
 * Reasons page might not be evictable:
3417
 * (1) page's mapping marked unevictable
N
Nick Piggin 已提交
3418
 * (2) page is part of an mlocked VMA
3419
 *
L
Lee Schermerhorn 已提交
3420
 */
3421
int page_evictable(struct page *page)
L
Lee Schermerhorn 已提交
3422
{
3423
	return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
L
Lee Schermerhorn 已提交
3424
}
3425

3426
#ifdef CONFIG_SHMEM
3427
/**
3428 3429 3430
 * 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
3431
 *
3432
 * Checks pages for evictability and moves them to the appropriate lru list.
3433 3434
 *
 * This function is only used for SysV IPC SHM_UNLOCK.
3435
 */
3436
void check_move_unevictable_pages(struct page **pages, int nr_pages)
3437
{
3438
	struct lruvec *lruvec;
3439 3440 3441 3442
	struct zone *zone = NULL;
	int pgscanned = 0;
	int pgrescued = 0;
	int i;
3443

3444 3445 3446
	for (i = 0; i < nr_pages; i++) {
		struct page *page = pages[i];
		struct zone *pagezone;
3447

3448 3449 3450 3451 3452 3453 3454 3455
		pgscanned++;
		pagezone = page_zone(page);
		if (pagezone != zone) {
			if (zone)
				spin_unlock_irq(&zone->lru_lock);
			zone = pagezone;
			spin_lock_irq(&zone->lru_lock);
		}
3456
		lruvec = mem_cgroup_page_lruvec(page, zone);
3457

3458 3459
		if (!PageLRU(page) || !PageUnevictable(page))
			continue;
3460

3461
		if (page_evictable(page)) {
3462 3463 3464 3465
			enum lru_list lru = page_lru_base_type(page);

			VM_BUG_ON(PageActive(page));
			ClearPageUnevictable(page);
3466 3467
			del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
			add_page_to_lru_list(page, lruvec, lru);
3468
			pgrescued++;
3469
		}
3470
	}
3471

3472 3473 3474 3475
	if (zone) {
		__count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
		__count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
		spin_unlock_irq(&zone->lru_lock);
3476 3477
	}
}
3478
#endif /* CONFIG_SHMEM */
3479

3480
static void warn_scan_unevictable_pages(void)
3481
{
3482
	printk_once(KERN_WARNING
3483
		    "%s: The scan_unevictable_pages sysctl/node-interface has been "
3484
		    "disabled for lack of a legitimate use case.  If you have "
3485 3486
		    "one, please send an email to linux-mm@kvack.org.\n",
		    current->comm);
3487 3488 3489 3490 3491 3492 3493 3494 3495
}

/*
 * 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,
3496
			   void __user *buffer,
3497 3498
			   size_t *length, loff_t *ppos)
{
3499
	warn_scan_unevictable_pages();
3500
	proc_doulongvec_minmax(table, write, buffer, length, ppos);
3501 3502 3503 3504
	scan_unevictable_pages = 0;
	return 0;
}

3505
#ifdef CONFIG_NUMA
3506 3507 3508 3509 3510
/*
 * per node 'scan_unevictable_pages' attribute.  On demand re-scan of
 * a specified node's per zone unevictable lists for evictable pages.
 */

3511 3512
static ssize_t read_scan_unevictable_node(struct device *dev,
					  struct device_attribute *attr,
3513 3514
					  char *buf)
{
3515
	warn_scan_unevictable_pages();
3516 3517 3518
	return sprintf(buf, "0\n");	/* always zero; should fit... */
}

3519 3520
static ssize_t write_scan_unevictable_node(struct device *dev,
					   struct device_attribute *attr,
3521 3522
					const char *buf, size_t count)
{
3523
	warn_scan_unevictable_pages();
3524 3525 3526 3527
	return 1;
}


3528
static DEVICE_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
3529 3530 3531 3532 3533
			read_scan_unevictable_node,
			write_scan_unevictable_node);

int scan_unevictable_register_node(struct node *node)
{
3534
	return device_create_file(&node->dev, &dev_attr_scan_unevictable_pages);
3535 3536 3537 3538
}

void scan_unevictable_unregister_node(struct node *node)
{
3539
	device_remove_file(&node->dev, &dev_attr_scan_unevictable_pages);
3540
}
3541
#endif