vmscan.c 96 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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	/*
	 * 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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};

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struct mem_cgroup_zone {
	struct mem_cgroup *mem_cgroup;
	struct zone *zone;
};

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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_CGROUP_MEM_RES_CTLR
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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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static bool scanning_global_lru(struct mem_cgroup_zone *mz)
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{
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	return !mz->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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static bool scanning_global_lru(struct mem_cgroup_zone *mz)
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{
	return true;
}
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#endif

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static struct zone_reclaim_stat *get_reclaim_stat(struct mem_cgroup_zone *mz)
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{
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	if (!scanning_global_lru(mz))
		return mem_cgroup_get_reclaim_stat(mz->mem_cgroup, mz->zone);
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	return &mz->zone->reclaim_stat;
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}

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static unsigned long zone_nr_lru_pages(struct mem_cgroup_zone *mz,
				       enum lru_list lru)
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{
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	if (!scanning_global_lru(mz))
		return mem_cgroup_zone_nr_lru_pages(mz->mem_cgroup,
						    zone_to_nid(mz->zone),
						    zone_idx(mz->zone),
						    BIT(lru));
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	return zone_page_state(mz->zone, 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);

	if (page_evictable(page, NULL)) {
		/*
		 * 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.
	 */
	if (lru == LRU_UNEVICTABLE && page_evictable(page, NULL)) {
		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.
		 */
	}

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	if (was_unevictable && lru != LRU_UNEVICTABLE)
		count_vm_event(UNEVICTABLE_PGRESCUED);
	else if (!was_unevictable && lru == LRU_UNEVICTABLE)
		count_vm_event(UNEVICTABLE_PGCULLED);

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	put_page(page);		/* drop ref from isolate */
}

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enum page_references {
	PAGEREF_RECLAIM,
	PAGEREF_RECLAIM_CLEAN,
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	PAGEREF_KEEP,
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	PAGEREF_ACTIVATE,
};

static enum page_references page_check_references(struct page *page,
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						  struct mem_cgroup_zone *mz,
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						  struct scan_control *sc)
{
645
	int referenced_ptes, referenced_page;
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	unsigned long vm_flags;

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	referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
					  &vm_flags);
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	referenced_page = TestClearPageReferenced(page);
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	/*
	 * 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;

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	if (referenced_ptes) {
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		if (PageSwapBacked(page))
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			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);

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		if (referenced_page || referenced_ptes > 1)
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			return PAGEREF_ACTIVATE;

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		/*
		 * Activate file-backed executable pages after first usage.
		 */
		if (vm_flags & VM_EXEC)
			return PAGEREF_ACTIVATE;

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		return PAGEREF_KEEP;
	}
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	/* Reclaim if clean, defer dirty pages to writeback */
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	if (referenced_page && !PageSwapBacked(page))
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		return PAGEREF_RECLAIM_CLEAN;

	return PAGEREF_RECLAIM;
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}

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/*
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 * shrink_page_list() returns the number of reclaimed pages
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 */
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static unsigned long shrink_page_list(struct list_head *page_list,
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				      struct mem_cgroup_zone *mz,
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				      struct scan_control *sc,
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				      int priority,
				      unsigned long *ret_nr_dirty,
				      unsigned long *ret_nr_writeback)
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{
	LIST_HEAD(ret_pages);
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	LIST_HEAD(free_pages);
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	int pgactivate = 0;
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	unsigned long nr_dirty = 0;
	unsigned long nr_congested = 0;
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	unsigned long nr_reclaimed = 0;
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	unsigned long nr_writeback = 0;
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	cond_resched();

	while (!list_empty(page_list)) {
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		enum page_references references;
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		struct address_space *mapping;
		struct page *page;
		int may_enter_fs;

		cond_resched();

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

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		if (!trylock_page(page))
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			goto keep;

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		VM_BUG_ON(PageActive(page));
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		VM_BUG_ON(page_zone(page) != mz->zone);
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		sc->nr_scanned++;
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		if (unlikely(!page_evictable(page, NULL)))
			goto cull_mlocked;
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		if (!sc->may_unmap && page_mapped(page))
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			goto keep_locked;

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		/* Double the slab pressure for mapped and swapcache pages */
		if (page_mapped(page) || PageSwapCache(page))
			sc->nr_scanned++;

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

		if (PageWriteback(page)) {
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			nr_writeback++;
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			unlock_page(page);
			goto keep;
753
		}
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		references = page_check_references(page, mz, sc);
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		switch (references) {
		case PAGEREF_ACTIVATE:
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			goto activate_locked;
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		case PAGEREF_KEEP:
			goto keep_locked;
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		case PAGEREF_RECLAIM:
		case PAGEREF_RECLAIM_CLEAN:
			; /* try to reclaim the page below */
		}
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		/*
		 * Anonymous process memory has backing store?
		 * Try to allocate it some swap space here.
		 */
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		if (PageAnon(page) && !PageSwapCache(page)) {
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			if (!(sc->gfp_mask & __GFP_IO))
				goto keep_locked;
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			if (!add_to_swap(page))
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				goto activate_locked;
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			may_enter_fs = 1;
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		}
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		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) {
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			switch (try_to_unmap(page, TTU_UNMAP)) {
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			case SWAP_FAIL:
				goto activate_locked;
			case SWAP_AGAIN:
				goto keep_locked;
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			case SWAP_MLOCK:
				goto cull_mlocked;
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			case SWAP_SUCCESS:
				; /* try to free the page below */
			}
		}

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

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			/*
			 * Only kswapd can writeback filesystem pages to
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			 * avoid risk of stack overflow but do not writeback
			 * unless under significant pressure.
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			 */
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			if (page_is_file_cache(page) &&
					(!current_is_kswapd() || priority >= DEF_PRIORITY - 2)) {
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				/*
				 * 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);

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				goto keep_locked;
			}

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			if (references == PAGEREF_RECLAIM_CLEAN)
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				goto keep_locked;
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			if (!may_enter_fs)
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				goto keep_locked;
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			if (!sc->may_writepage)
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				goto keep_locked;

			/* Page is dirty, try to write it out here */
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			switch (pageout(page, mapping, sc)) {
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			case PAGE_KEEP:
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				nr_congested++;
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				goto keep_locked;
			case PAGE_ACTIVATE:
				goto activate_locked;
			case PAGE_SUCCESS:
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				if (PageWriteback(page))
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					goto keep;
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				if (PageDirty(page))
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					goto keep;
838

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				/*
				 * A synchronous write - probably a ramdisk.  Go
				 * ahead and try to reclaim the page.
				 */
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				if (!trylock_page(page))
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					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
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		 * will do this, as well as the blockdev mapping.
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		 * 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.
		 */
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		if (page_has_private(page)) {
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			if (!try_to_release_page(page, sc->gfp_mask))
				goto activate_locked;
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			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;
				}
			}
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		}

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		if (!mapping || !__remove_mapping(mapping, page))
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			goto keep_locked;
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		/*
		 * 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);
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free_it:
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		nr_reclaimed++;
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		/*
		 * Is there need to periodically free_page_list? It would
		 * appear not as the counts should be low
		 */
		list_add(&page->lru, &free_pages);
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		continue;

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cull_mlocked:
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		if (PageSwapCache(page))
			try_to_free_swap(page);
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		unlock_page(page);
		putback_lru_page(page);
		continue;

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activate_locked:
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		/* Not a candidate for swapping, so reclaim swap space. */
		if (PageSwapCache(page) && vm_swap_full())
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			try_to_free_swap(page);
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		VM_BUG_ON(PageActive(page));
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		SetPageActive(page);
		pgactivate++;
keep_locked:
		unlock_page(page);
keep:
		list_add(&page->lru, &ret_pages);
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		VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
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	}
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	/*
	 * 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
	 */
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	if (nr_dirty && nr_dirty == nr_congested && global_reclaim(sc))
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		zone_set_flag(mz->zone, ZONE_CONGESTED);
945

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	free_hot_cold_page_list(&free_pages, 1);
947

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	list_splice(&ret_pages, page_list);
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	count_vm_events(PGACTIVATE, pgactivate);
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	*ret_nr_dirty += nr_dirty;
	*ret_nr_writeback += nr_writeback;
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	return nr_reclaimed;
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}

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/*
 * 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.
 */
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int __isolate_lru_page(struct page *page, isolate_mode_t mode, int file)
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{
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	bool all_lru_mode;
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	int ret = -EINVAL;

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

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	all_lru_mode = (mode & (ISOLATE_ACTIVE|ISOLATE_INACTIVE)) ==
		(ISOLATE_ACTIVE|ISOLATE_INACTIVE);

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	/*
	 * When checking the active state, we need to be sure we are
	 * dealing with comparible boolean values.  Take the logical not
	 * of each.
	 */
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	if (!all_lru_mode && !PageActive(page) != !(mode & ISOLATE_ACTIVE))
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		return ret;

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	if (!all_lru_mode && !!page_is_file_cache(page) != file)
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		return ret;

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	/* Do not give back unevictable pages for compaction */
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	if (PageUnevictable(page))
		return ret;

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	ret = -EBUSY;
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	/*
	 * 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;
		}
	}
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	if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
		return ret;

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	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;
}

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/*
 * 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.
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 * @mz:		The mem_cgroup_zone to pull pages from.
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 * @dst:	The temp list to put pages on to.
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 * @nr_scanned:	The number of pages that were scanned.
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 * @sc:		The scan_control struct for this reclaim session
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 * @mode:	One of the LRU isolation modes
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 * @active:	True [1] if isolating active pages
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 * @file:	True [1] if isolating file [!anon] pages
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 *
 * returns how many pages were moved onto *@dst.
 */
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static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
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		struct mem_cgroup_zone *mz, struct list_head *dst,
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		unsigned long *nr_scanned, struct scan_control *sc,
		isolate_mode_t mode, int active, int file)
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{
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	struct lruvec *lruvec;
	struct list_head *src;
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	unsigned long nr_taken = 0;
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	unsigned long scan;
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	int lru = LRU_BASE;

	lruvec = mem_cgroup_zone_lruvec(mz->zone, mz->mem_cgroup);
	if (active)
		lru += LRU_ACTIVE;
	if (file)
		lru += LRU_FILE;
	src = &lruvec->lists[lru];
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	for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
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		struct page *page;

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		page = lru_to_page(src);
		prefetchw_prev_lru_page(page, src, flags);

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		VM_BUG_ON(!PageLRU(page));
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		switch (__isolate_lru_page(page, mode, file)) {
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		case 0:
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			mem_cgroup_lru_del(page);
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			list_move(&page->lru, dst);
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			nr_taken += hpage_nr_pages(page);
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			break;

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

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	*nr_scanned = scan;
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	trace_mm_vmscan_lru_isolate(sc->order,
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			nr_to_scan, scan,
			nr_taken,
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			mode, file);
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	return nr_taken;
}

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/**
 * 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
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 * 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.
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 *
 * 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;

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	VM_BUG_ON(!page_count(page));

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	if (PageLRU(page)) {
		struct zone *zone = page_zone(page);

		spin_lock_irq(&zone->lru_lock);
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		if (PageLRU(page)) {
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			int lru = page_lru(page);
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			ret = 0;
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			get_page(page);
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			ClearPageLRU(page);
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			del_page_from_lru_list(zone, page, lru);
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		}
		spin_unlock_irq(&zone->lru_lock);
	}
	return ret;
}

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/*
 * Are there way too many processes in the direct reclaim path already?
 */
static int too_many_isolated(struct zone *zone, int file,
		struct scan_control *sc)
{
	unsigned long inactive, isolated;

	if (current_is_kswapd())
		return 0;

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	if (!global_reclaim(sc))
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		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);
	}

	return isolated > inactive;
}

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static noinline_for_stack void
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putback_inactive_pages(struct mem_cgroup_zone *mz,
		       struct list_head *page_list)
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{
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	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(mz);
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	struct zone *zone = mz->zone;
	LIST_HEAD(pages_to_free);
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	/*
	 * Put back any unfreeable pages.
	 */
	while (!list_empty(page_list)) {
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		struct page *page = lru_to_page(page_list);
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		int lru;
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		VM_BUG_ON(PageLRU(page));
		list_del(&page->lru);
		if (unlikely(!page_evictable(page, NULL))) {
			spin_unlock_irq(&zone->lru_lock);
			putback_lru_page(page);
			spin_lock_irq(&zone->lru_lock);
			continue;
		}
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		SetPageLRU(page);
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		lru = page_lru(page);
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		add_page_to_lru_list(zone, page, lru);
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		if (is_active_lru(lru)) {
			int file = is_file_lru(lru);
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			int numpages = hpage_nr_pages(page);
			reclaim_stat->recent_rotated[file] += numpages;
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		}
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		if (put_page_testzero(page)) {
			__ClearPageLRU(page);
			__ClearPageActive(page);
			del_page_from_lru_list(zone, page, lru);

			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);
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		}
	}

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

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static noinline_for_stack void
update_isolated_counts(struct mem_cgroup_zone *mz,
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		       struct list_head *page_list,
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		       unsigned long *nr_anon,
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		       unsigned long *nr_file)
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{
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	struct zone *zone = mz->zone;
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	unsigned int count[NR_LRU_LISTS] = { 0, };
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	unsigned long nr_active = 0;
	struct page *page;
	int lru;

	/*
	 * Count pages and clear active flags
	 */
	list_for_each_entry(page, page_list, lru) {
		int numpages = hpage_nr_pages(page);
		lru = page_lru_base_type(page);
		if (PageActive(page)) {
			lru += LRU_ACTIVE;
			ClearPageActive(page);
			nr_active += numpages;
		}
		count[lru] += numpages;
	}
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	preempt_disable();
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	__count_vm_events(PGDEACTIVATE, nr_active);

	__mod_zone_page_state(zone, NR_ACTIVE_FILE,
			      -count[LRU_ACTIVE_FILE]);
	__mod_zone_page_state(zone, NR_INACTIVE_FILE,
			      -count[LRU_INACTIVE_FILE]);
	__mod_zone_page_state(zone, NR_ACTIVE_ANON,
			      -count[LRU_ACTIVE_ANON]);
	__mod_zone_page_state(zone, NR_INACTIVE_ANON,
			      -count[LRU_INACTIVE_ANON]);

	*nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
	*nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];

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	__mod_zone_page_state(zone, NR_ISOLATED_ANON, *nr_anon);
	__mod_zone_page_state(zone, NR_ISOLATED_FILE, *nr_file);
	preempt_enable();
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}

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/*
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 * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
 * of reclaimed pages
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 */
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static noinline_for_stack unsigned long
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shrink_inactive_list(unsigned long nr_to_scan, struct mem_cgroup_zone *mz,
		     struct scan_control *sc, int priority, int file)
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{
	LIST_HEAD(page_list);
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	unsigned long nr_scanned;
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	unsigned long nr_reclaimed = 0;
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	unsigned long nr_taken;
	unsigned long nr_anon;
	unsigned long nr_file;
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	unsigned long nr_dirty = 0;
	unsigned long nr_writeback = 0;
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	isolate_mode_t isolate_mode = ISOLATE_INACTIVE;
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	struct zone *zone = mz->zone;
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	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(mz);
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	while (unlikely(too_many_isolated(zone, file, sc))) {
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		congestion_wait(BLK_RW_ASYNC, HZ/10);
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		/* We are about to die and free our memory. Return now. */
		if (fatal_signal_pending(current))
			return SWAP_CLUSTER_MAX;
	}

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	lru_add_drain();
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	if (!sc->may_unmap)
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		isolate_mode |= ISOLATE_UNMAPPED;
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	if (!sc->may_writepage)
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		isolate_mode |= ISOLATE_CLEAN;
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	spin_lock_irq(&zone->lru_lock);
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	nr_taken = isolate_lru_pages(nr_to_scan, mz, &page_list, &nr_scanned,
				     sc, isolate_mode, 0, file);
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	if (global_reclaim(sc)) {
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		zone->pages_scanned += nr_scanned;
		if (current_is_kswapd())
			__count_zone_vm_events(PGSCAN_KSWAPD, zone,
					       nr_scanned);
		else
			__count_zone_vm_events(PGSCAN_DIRECT, zone,
					       nr_scanned);
	}
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	spin_unlock_irq(&zone->lru_lock);
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1337
	if (nr_taken == 0)
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		return 0;
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	update_isolated_counts(mz, &page_list, &nr_anon, &nr_file);

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	nr_reclaimed = shrink_page_list(&page_list, mz, sc, priority,
1343
						&nr_dirty, &nr_writeback);
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	spin_lock_irq(&zone->lru_lock);

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	reclaim_stat->recent_scanned[0] += nr_anon;
	reclaim_stat->recent_scanned[1] += nr_file;

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	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);
	}
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	putback_inactive_pages(mz, &page_list);

	__mod_zone_page_state(zone, NR_ISOLATED_ANON, -nr_anon);
	__mod_zone_page_state(zone, NR_ISOLATED_FILE, -nr_file);

	spin_unlock_irq(&zone->lru_lock);

	free_hot_cold_page_list(&page_list, 1);
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	/*
	 * 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
	 */
	if (nr_writeback && nr_writeback >= (nr_taken >> (DEF_PRIORITY-priority)))
		wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);

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	trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
		zone_idx(zone),
		nr_scanned, nr_reclaimed,
		priority,
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		trace_shrink_flags(file));
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	return nr_reclaimed;
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}

/*
 * 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.
 */
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static void move_active_pages_to_lru(struct zone *zone,
				     struct list_head *list,
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				     struct list_head *pages_to_free,
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				     enum lru_list lru)
{
	unsigned long pgmoved = 0;
	struct page *page;

	while (!list_empty(list)) {
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		struct lruvec *lruvec;

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		page = lru_to_page(list);

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

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		lruvec = mem_cgroup_lru_add_list(zone, page, lru);
		list_move(&page->lru, &lruvec->lists[lru]);
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		pgmoved += hpage_nr_pages(page);
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		if (put_page_testzero(page)) {
			__ClearPageLRU(page);
			__ClearPageActive(page);
			del_page_from_lru_list(zone, page, lru);

			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);
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		}
	}
	__mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
	if (!is_active_lru(lru))
		__count_vm_events(PGDEACTIVATE, pgmoved);
}
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static void shrink_active_list(unsigned long nr_to_scan,
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			       struct mem_cgroup_zone *mz,
			       struct scan_control *sc,
			       int priority, int file)
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{
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	unsigned long nr_taken;
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	unsigned long nr_scanned;
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	unsigned long vm_flags;
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	LIST_HEAD(l_hold);	/* The pages which were snipped off */
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	LIST_HEAD(l_active);
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	LIST_HEAD(l_inactive);
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	struct page *page;
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	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(mz);
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	unsigned long nr_rotated = 0;
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	isolate_mode_t isolate_mode = ISOLATE_ACTIVE;
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	struct zone *zone = mz->zone;
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	lru_add_drain();
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	if (!sc->may_unmap)
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		isolate_mode |= ISOLATE_UNMAPPED;
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	if (!sc->may_writepage)
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		isolate_mode |= ISOLATE_CLEAN;
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	spin_lock_irq(&zone->lru_lock);
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1484
	nr_taken = isolate_lru_pages(nr_to_scan, mz, &l_hold, &nr_scanned, sc,
1485
				     isolate_mode, 1, file);
1486
	if (global_reclaim(sc))
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		zone->pages_scanned += nr_scanned;
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	reclaim_stat->recent_scanned[file] += nr_taken;
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	__count_zone_vm_events(PGREFILL, zone, nr_scanned);
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	if (file)
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		__mod_zone_page_state(zone, NR_ACTIVE_FILE, -nr_taken);
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	else
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		__mod_zone_page_state(zone, NR_ACTIVE_ANON, -nr_taken);
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	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
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	spin_unlock_irq(&zone->lru_lock);

	while (!list_empty(&l_hold)) {
		cond_resched();
		page = lru_to_page(&l_hold);
		list_del(&page->lru);
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		if (unlikely(!page_evictable(page, NULL))) {
			putback_lru_page(page);
			continue;
		}

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		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);
			}
		}

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		if (page_referenced(page, 0, sc->target_mem_cgroup,
				    &vm_flags)) {
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			nr_rotated += hpage_nr_pages(page);
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			/*
			 * 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.
			 */
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			if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
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				list_add(&page->lru, &l_active);
				continue;
			}
		}
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		ClearPageActive(page);	/* we are de-activating */
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		list_add(&page->lru, &l_inactive);
	}

1539
	/*
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	 * Move pages back to the lru list.
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	 */
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	spin_lock_irq(&zone->lru_lock);
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	/*
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	 * 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.
1548
	 */
1549
	reclaim_stat->recent_rotated[file] += nr_rotated;
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1551
	move_active_pages_to_lru(zone, &l_active, &l_hold,
1552
						LRU_ACTIVE + file * LRU_FILE);
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	move_active_pages_to_lru(zone, &l_inactive, &l_hold,
1554
						LRU_BASE   + file * LRU_FILE);
1555
	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1556
	spin_unlock_irq(&zone->lru_lock);
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	free_hot_cold_page_list(&l_hold, 1);
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}

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#ifdef CONFIG_SWAP
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static int inactive_anon_is_low_global(struct zone *zone)
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{
	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;
}

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/**
 * inactive_anon_is_low - check if anonymous pages need to be deactivated
 * @zone: zone to check
 * @sc:   scan control of this context
 *
 * Returns true if the zone does not have enough inactive anon pages,
 * meaning some active anon pages need to be deactivated.
 */
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static int inactive_anon_is_low(struct mem_cgroup_zone *mz)
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{
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	/*
	 * If we don't have swap space, anonymous page deactivation
	 * is pointless.
	 */
	if (!total_swap_pages)
		return 0;

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	if (!scanning_global_lru(mz))
		return mem_cgroup_inactive_anon_is_low(mz->mem_cgroup,
						       mz->zone);

	return inactive_anon_is_low_global(mz->zone);
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}
1598
#else
1599
static inline int inactive_anon_is_low(struct mem_cgroup_zone *mz)
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{
	return 0;
}
#endif
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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
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 * @mz: memory cgroup and zone to check
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 *
 * 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.
 */
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static int inactive_file_is_low(struct mem_cgroup_zone *mz)
1630
{
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	if (!scanning_global_lru(mz))
		return mem_cgroup_inactive_file_is_low(mz->mem_cgroup,
						       mz->zone);
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1635
	return inactive_file_is_low_global(mz->zone);
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}

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static int inactive_list_is_low(struct mem_cgroup_zone *mz, int file)
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{
	if (file)
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		return inactive_file_is_low(mz);
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	else
1643
		return inactive_anon_is_low(mz);
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}

1646
static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
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				 struct mem_cgroup_zone *mz,
				 struct scan_control *sc, int priority)
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{
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	int file = is_file_lru(lru);

1652
	if (is_active_lru(lru)) {
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		if (inactive_list_is_low(mz, file))
			shrink_active_list(nr_to_scan, mz, sc, priority, file);
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		return 0;
	}

1658
	return shrink_inactive_list(nr_to_scan, mz, sc, priority, file);
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}

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static int vmscan_swappiness(struct mem_cgroup_zone *mz,
			     struct scan_control *sc)
1663
{
1664
	if (global_reclaim(sc))
1665
		return vm_swappiness;
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	return mem_cgroup_swappiness(mz->mem_cgroup);
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}

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/*
 * 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.
 *
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 * nr[0] = anon pages to scan; nr[1] = file pages to scan
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 */
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static void get_scan_count(struct mem_cgroup_zone *mz, struct scan_control *sc,
			   unsigned long *nr, int priority)
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{
	unsigned long anon, file, free;
	unsigned long anon_prio, file_prio;
	unsigned long ap, fp;
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	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(mz);
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	u64 fraction[2], denominator;
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	enum lru_list lru;
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	int noswap = 0;
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	bool force_scan = false;
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	/*
	 * 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.
	 */
1699
	if (current_is_kswapd() && mz->zone->all_unreclaimable)
1700
		force_scan = true;
1701
	if (!global_reclaim(sc))
1702
		force_scan = true;
1703 1704 1705 1706 1707 1708 1709 1710 1711

	/* 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;
	}
1712

1713 1714 1715 1716
	anon  = zone_nr_lru_pages(mz, LRU_ACTIVE_ANON) +
		zone_nr_lru_pages(mz, LRU_INACTIVE_ANON);
	file  = zone_nr_lru_pages(mz, LRU_ACTIVE_FILE) +
		zone_nr_lru_pages(mz, LRU_INACTIVE_FILE);
1717

1718
	if (global_reclaim(sc)) {
1719
		free  = zone_page_state(mz->zone, NR_FREE_PAGES);
1720 1721
		/* If we have very few page cache pages,
		   force-scan anon pages. */
1722
		if (unlikely(file + free <= high_wmark_pages(mz->zone))) {
1723 1724 1725 1726
			fraction[0] = 1;
			fraction[1] = 0;
			denominator = 1;
			goto out;
1727
		}
1728 1729
	}

1730 1731 1732 1733
	/*
	 * With swappiness at 100, anonymous and file have the same priority.
	 * This scanning priority is essentially the inverse of IO cost.
	 */
1734 1735
	anon_prio = vmscan_swappiness(mz, sc);
	file_prio = 200 - vmscan_swappiness(mz, sc);
1736

1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747
	/*
	 * 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]
	 */
1748
	spin_lock_irq(&mz->zone->lru_lock);
1749 1750 1751
	if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
		reclaim_stat->recent_scanned[0] /= 2;
		reclaim_stat->recent_rotated[0] /= 2;
1752 1753
	}

1754 1755 1756
	if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
		reclaim_stat->recent_scanned[1] /= 2;
		reclaim_stat->recent_rotated[1] /= 2;
1757 1758 1759
	}

	/*
1760 1761 1762
	 * 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.
1763
	 */
1764
	ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
1765
	ap /= reclaim_stat->recent_rotated[0] + 1;
1766

1767
	fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
1768
	fp /= reclaim_stat->recent_rotated[1] + 1;
1769
	spin_unlock_irq(&mz->zone->lru_lock);
1770

1771 1772 1773 1774
	fraction[0] = ap;
	fraction[1] = fp;
	denominator = ap + fp + 1;
out:
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1775 1776
	for_each_evictable_lru(lru) {
		int file = is_file_lru(lru);
1777
		unsigned long scan;
1778

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1779
		scan = zone_nr_lru_pages(mz, lru);
1780
		if (priority || noswap || !vmscan_swappiness(mz, sc)) {
1781
			scan >>= priority;
1782 1783
			if (!scan && force_scan)
				scan = SWAP_CLUSTER_MAX;
1784 1785
			scan = div64_u64(scan * fraction[file], denominator);
		}
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1786
		nr[lru] = scan;
1787
	}
1788
}
1789

1790 1791 1792 1793 1794 1795 1796 1797 1798 1799 1800
/* Use reclaim/compaction for costly allocs or under memory pressure */
static bool in_reclaim_compaction(int priority, struct scan_control *sc)
{
	if (COMPACTION_BUILD && sc->order &&
			(sc->order > PAGE_ALLOC_COSTLY_ORDER ||
			 priority < DEF_PRIORITY - 2))
		return true;

	return false;
}

1801
/*
1802 1803 1804 1805 1806
 * 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.
1807
 */
1808
static inline bool should_continue_reclaim(struct mem_cgroup_zone *mz,
1809 1810
					unsigned long nr_reclaimed,
					unsigned long nr_scanned,
1811
					int priority,
1812 1813 1814 1815 1816 1817
					struct scan_control *sc)
{
	unsigned long pages_for_compaction;
	unsigned long inactive_lru_pages;

	/* If not in reclaim/compaction mode, stop */
1818
	if (!in_reclaim_compaction(priority, sc))
1819 1820
		return false;

1821 1822 1823 1824 1825 1826 1827 1828 1829 1830 1831 1832 1833 1834 1835 1836 1837 1838 1839 1840 1841 1842
	/* 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;
	}
1843 1844 1845 1846 1847 1848

	/*
	 * If we have not reclaimed enough pages for compaction and the
	 * inactive lists are large enough, continue reclaiming
	 */
	pages_for_compaction = (2UL << sc->order);
1849
	inactive_lru_pages = zone_nr_lru_pages(mz, LRU_INACTIVE_FILE);
1850
	if (nr_swap_pages > 0)
1851
		inactive_lru_pages += zone_nr_lru_pages(mz, LRU_INACTIVE_ANON);
1852 1853 1854 1855 1856
	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 */
1857
	switch (compaction_suitable(mz->zone, sc->order)) {
1858 1859 1860 1861 1862 1863 1864 1865
	case COMPACT_PARTIAL:
	case COMPACT_CONTINUE:
		return false;
	default:
		return true;
	}
}

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1866 1867 1868
/*
 * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
 */
1869 1870
static void shrink_mem_cgroup_zone(int priority, struct mem_cgroup_zone *mz,
				   struct scan_control *sc)
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1871
{
1872
	unsigned long nr[NR_LRU_LISTS];
1873
	unsigned long nr_to_scan;
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1874
	enum lru_list lru;
1875
	unsigned long nr_reclaimed, nr_scanned;
1876
	unsigned long nr_to_reclaim = sc->nr_to_reclaim;
1877
	struct blk_plug plug;
1878

1879 1880
restart:
	nr_reclaimed = 0;
1881
	nr_scanned = sc->nr_scanned;
1882
	get_scan_count(mz, sc, nr, priority);
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1883

1884
	blk_start_plug(&plug);
1885 1886
	while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
					nr[LRU_INACTIVE_FILE]) {
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1887 1888
		for_each_evictable_lru(lru) {
			if (nr[lru]) {
1889
				nr_to_scan = min_t(unsigned long,
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1890 1891
						   nr[lru], SWAP_CLUSTER_MAX);
				nr[lru] -= nr_to_scan;
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1892

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1893
				nr_reclaimed += shrink_list(lru, nr_to_scan,
1894
							    mz, sc, priority);
1895
			}
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1896
		}
1897 1898 1899 1900 1901 1902 1903 1904
		/*
		 * 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.
		 */
1905
		if (nr_reclaimed >= nr_to_reclaim && priority < DEF_PRIORITY)
1906
			break;
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1907
	}
1908
	blk_finish_plug(&plug);
1909
	sc->nr_reclaimed += nr_reclaimed;
1910

1911 1912 1913 1914
	/*
	 * Even if we did not try to evict anon pages at all, we want to
	 * rebalance the anon lru active/inactive ratio.
	 */
1915 1916
	if (inactive_anon_is_low(mz))
		shrink_active_list(SWAP_CLUSTER_MAX, mz, sc, priority, 0);
1917

1918
	/* reclaim/compaction might need reclaim to continue */
1919
	if (should_continue_reclaim(mz, nr_reclaimed,
1920 1921
					sc->nr_scanned - nr_scanned,
					priority, sc))
1922 1923
		goto restart;

1924
	throttle_vm_writeout(sc->gfp_mask);
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1925 1926
}

1927 1928 1929
static void shrink_zone(int priority, struct zone *zone,
			struct scan_control *sc)
{
1930 1931
	struct mem_cgroup *root = sc->target_mem_cgroup;
	struct mem_cgroup_reclaim_cookie reclaim = {
1932
		.zone = zone,
1933
		.priority = priority,
1934
	};
1935 1936 1937 1938 1939 1940 1941 1942
	struct mem_cgroup *memcg;

	memcg = mem_cgroup_iter(root, NULL, &reclaim);
	do {
		struct mem_cgroup_zone mz = {
			.mem_cgroup = memcg,
			.zone = zone,
		};
1943

1944 1945 1946 1947 1948 1949
		shrink_mem_cgroup_zone(priority, &mz, sc);
		/*
		 * 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.
1950 1951 1952 1953
		 *
		 * Direct reclaim and kswapd, on the other hand, have
		 * to scan all memory cgroups to fulfill the overall
		 * scan target for the zone.
1954 1955 1956 1957 1958 1959 1960
		 */
		if (!global_reclaim(sc)) {
			mem_cgroup_iter_break(root, memcg);
			break;
		}
		memcg = mem_cgroup_iter(root, memcg, &reclaim);
	} while (memcg);
1961 1962
}

1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988
/* 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
	 */
1989
	if (compaction_deferred(zone, sc->order))
1990 1991 1992 1993 1994 1995 1996 1997 1998
		return watermark_ok;

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

	return watermark_ok;
}

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1999 2000 2001 2002 2003
/*
 * 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.
 *
2004 2005
 * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
 * Because:
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2006 2007
 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
 *    allocation or
2008 2009 2010
 * 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.
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2011 2012 2013
 *
 * If a zone is deemed to be full of pinned pages then just give it a light
 * scan then give up on it.
2014 2015
 *
 * This function returns true if a zone is being reclaimed for a costly
2016
 * high-order allocation and compaction is ready to begin. This indicates to
2017 2018
 * the caller that it should consider retrying the allocation instead of
 * further reclaim.
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2019
 */
2020
static bool shrink_zones(int priority, struct zonelist *zonelist,
2021
					struct scan_control *sc)
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2022
{
2023
	struct zoneref *z;
2024
	struct zone *zone;
2025 2026
	unsigned long nr_soft_reclaimed;
	unsigned long nr_soft_scanned;
2027
	bool aborted_reclaim = false;
2028

2029 2030 2031 2032 2033 2034 2035 2036
	/*
	 * 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;

2037 2038
	for_each_zone_zonelist_nodemask(zone, z, zonelist,
					gfp_zone(sc->gfp_mask), sc->nodemask) {
2039
		if (!populated_zone(zone))
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2040
			continue;
2041 2042 2043 2044
		/*
		 * Take care memory controller reclaiming has small influence
		 * to global LRU.
		 */
2045
		if (global_reclaim(sc)) {
2046 2047
			if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
				continue;
2048
			if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2049
				continue;	/* Let kswapd poll it */
2050 2051
			if (COMPACTION_BUILD) {
				/*
2052 2053 2054 2055 2056
				 * 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
2057 2058
				 * noticeable problem, like transparent huge
				 * page allocations.
2059
				 */
2060
				if (compaction_ready(zone, sc)) {
2061
					aborted_reclaim = true;
2062
					continue;
2063
				}
2064
			}
2065 2066 2067 2068 2069 2070 2071 2072 2073 2074 2075 2076 2077
			/*
			 * 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() */
2078
		}
2079

2080
		shrink_zone(priority, zone, sc);
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2081
	}
2082

2083
	return aborted_reclaim;
2084 2085 2086 2087 2088 2089 2090
}

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

2091
/* All zones in zonelist are unreclaimable? */
2092 2093 2094 2095 2096 2097 2098 2099 2100 2101 2102 2103
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;
2104 2105
		if (!zone->all_unreclaimable)
			return false;
2106 2107
	}

2108
	return true;
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2109
}
2110

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2111 2112 2113 2114 2115 2116 2117 2118
/*
 * 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
2119 2120 2121 2122
 * 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.
2123 2124 2125
 *
 * returns:	0, if no pages reclaimed
 * 		else, the number of pages reclaimed
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2126
 */
2127
static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2128 2129
					struct scan_control *sc,
					struct shrink_control *shrink)
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2130 2131
{
	int priority;
2132
	unsigned long total_scanned = 0;
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2133
	struct reclaim_state *reclaim_state = current->reclaim_state;
2134
	struct zoneref *z;
2135
	struct zone *zone;
2136
	unsigned long writeback_threshold;
2137
	bool aborted_reclaim;
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2138

2139 2140
	delayacct_freepages_start();

2141
	if (global_reclaim(sc))
2142
		count_vm_event(ALLOCSTALL);
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2143 2144

	for (priority = DEF_PRIORITY; priority >= 0; priority--) {
2145
		sc->nr_scanned = 0;
2146
		aborted_reclaim = shrink_zones(priority, zonelist, sc);
2147

2148 2149 2150 2151
		/*
		 * Don't shrink slabs when reclaiming memory from
		 * over limit cgroups
		 */
2152
		if (global_reclaim(sc)) {
2153
			unsigned long lru_pages = 0;
2154 2155
			for_each_zone_zonelist(zone, z, zonelist,
					gfp_zone(sc->gfp_mask)) {
2156 2157 2158 2159 2160 2161
				if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
					continue;

				lru_pages += zone_reclaimable_pages(zone);
			}

2162
			shrink_slab(shrink, sc->nr_scanned, lru_pages);
2163
			if (reclaim_state) {
2164
				sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2165 2166
				reclaim_state->reclaimed_slab = 0;
			}
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2167
		}
2168
		total_scanned += sc->nr_scanned;
2169
		if (sc->nr_reclaimed >= sc->nr_to_reclaim)
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2170 2171 2172 2173 2174 2175 2176 2177 2178
			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.
		 */
2179 2180
		writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
		if (total_scanned > writeback_threshold) {
2181 2182
			wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
						WB_REASON_TRY_TO_FREE_PAGES);
2183
			sc->may_writepage = 1;
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2184 2185 2186
		}

		/* Take a nap, wait for some writeback to complete */
2187
		if (!sc->hibernation_mode && sc->nr_scanned &&
2188 2189 2190 2191
		    priority < DEF_PRIORITY - 2) {
			struct zone *preferred_zone;

			first_zones_zonelist(zonelist, gfp_zone(sc->gfp_mask),
2192 2193
						&cpuset_current_mems_allowed,
						&preferred_zone);
2194 2195
			wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/10);
		}
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2196
	}
2197

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2198
out:
2199 2200
	delayacct_freepages_end();

2201 2202 2203
	if (sc->nr_reclaimed)
		return sc->nr_reclaimed;

2204 2205 2206 2207 2208 2209 2210 2211
	/*
	 * 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;

2212 2213
	/* Aborted reclaim to try compaction? don't OOM, then */
	if (aborted_reclaim)
2214 2215
		return 1;

2216
	/* top priority shrink_zones still had more to do? don't OOM, then */
2217
	if (global_reclaim(sc) && !all_unreclaimable(zonelist, sc))
2218 2219 2220
		return 1;

	return 0;
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}

2223
unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2224
				gfp_t gfp_mask, nodemask_t *nodemask)
2225
{
2226
	unsigned long nr_reclaimed;
2227 2228 2229
	struct scan_control sc = {
		.gfp_mask = gfp_mask,
		.may_writepage = !laptop_mode,
2230
		.nr_to_reclaim = SWAP_CLUSTER_MAX,
2231
		.may_unmap = 1,
2232
		.may_swap = 1,
2233
		.order = order,
2234
		.target_mem_cgroup = NULL,
2235
		.nodemask = nodemask,
2236
	};
2237 2238 2239
	struct shrink_control shrink = {
		.gfp_mask = sc.gfp_mask,
	};
2240

2241 2242 2243 2244
	trace_mm_vmscan_direct_reclaim_begin(order,
				sc.may_writepage,
				gfp_mask);

2245
	nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2246 2247 2248 2249

	trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);

	return nr_reclaimed;
2250 2251
}

2252
#ifdef CONFIG_CGROUP_MEM_RES_CTLR
2253

2254
unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
2255
						gfp_t gfp_mask, bool noswap,
2256 2257
						struct zone *zone,
						unsigned long *nr_scanned)
2258 2259
{
	struct scan_control sc = {
2260
		.nr_scanned = 0,
2261
		.nr_to_reclaim = SWAP_CLUSTER_MAX,
2262 2263 2264 2265
		.may_writepage = !laptop_mode,
		.may_unmap = 1,
		.may_swap = !noswap,
		.order = 0,
2266
		.target_mem_cgroup = memcg,
2267
	};
2268
	struct mem_cgroup_zone mz = {
2269
		.mem_cgroup = memcg,
2270 2271
		.zone = zone,
	};
2272

2273 2274
	sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
			(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2275 2276 2277 2278 2279

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

2280 2281 2282 2283 2284 2285 2286
	/*
	 * 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.
	 */
2287
	shrink_mem_cgroup_zone(0, &mz, &sc);
2288 2289 2290

	trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);

2291
	*nr_scanned = sc.nr_scanned;
2292 2293 2294
	return sc.nr_reclaimed;
}

2295
unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
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2296
					   gfp_t gfp_mask,
2297
					   bool noswap)
2298
{
2299
	struct zonelist *zonelist;
2300
	unsigned long nr_reclaimed;
2301
	int nid;
2302 2303
	struct scan_control sc = {
		.may_writepage = !laptop_mode,
2304
		.may_unmap = 1,
2305
		.may_swap = !noswap,
2306
		.nr_to_reclaim = SWAP_CLUSTER_MAX,
2307
		.order = 0,
2308
		.target_mem_cgroup = memcg,
2309
		.nodemask = NULL, /* we don't care the placement */
2310 2311 2312 2313 2314
		.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
				(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
	};
	struct shrink_control shrink = {
		.gfp_mask = sc.gfp_mask,
2315 2316
	};

2317 2318 2319 2320 2321
	/*
	 * 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.
	 */
2322
	nid = mem_cgroup_select_victim_node(memcg);
2323 2324

	zonelist = NODE_DATA(nid)->node_zonelists;
2325 2326 2327 2328 2329

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

2330
	nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2331 2332 2333 2334

	trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);

	return nr_reclaimed;
2335 2336 2337
}
#endif

2338 2339 2340
static void age_active_anon(struct zone *zone, struct scan_control *sc,
			    int priority)
{
2341
	struct mem_cgroup *memcg;
2342

2343 2344 2345 2346 2347 2348 2349 2350 2351 2352 2353 2354 2355 2356 2357 2358
	if (!total_swap_pages)
		return;

	memcg = mem_cgroup_iter(NULL, NULL, NULL);
	do {
		struct mem_cgroup_zone mz = {
			.mem_cgroup = memcg,
			.zone = zone,
		};

		if (inactive_anon_is_low(&mz))
			shrink_active_list(SWAP_CLUSTER_MAX, &mz,
					   sc, priority, 0);

		memcg = mem_cgroup_iter(NULL, memcg, NULL);
	} while (memcg);
2359 2360
}

2361 2362 2363 2364 2365 2366 2367 2368 2369 2370 2371
/*
 * pgdat_balanced is used when checking if a node is balanced for high-order
 * allocations. Only zones that meet watermarks and are in a zone allowed
 * by the callers classzone_idx are added to balanced_pages. The total of
 * balanced pages must be at least 25% of the zones allowed by classzone_idx
 * for the node to be considered balanced. Forcing all zones to be balanced
 * for high orders can cause excessive reclaim when there are imbalanced zones.
 * The choice of 25% is due to
 *   o a 16M DMA zone that is balanced will not balance a zone on any
 *     reasonable sized machine
 *   o On all other machines, the top zone must be at least a reasonable
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2372
 *     percentage of the middle zones. For example, on 32-bit x86, highmem
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 *     would need to be at least 256M for it to be balance a whole node.
 *     Similarly, on x86-64 the Normal zone would need to be at least 1G
 *     to balance a node on its own. These seemed like reasonable ratios.
 */
static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages,
						int classzone_idx)
{
	unsigned long present_pages = 0;
	int i;

	for (i = 0; i <= classzone_idx; i++)
		present_pages += pgdat->node_zones[i].present_pages;

2386 2387
	/* A special case here: if zone has no page, we think it's balanced */
	return balanced_pages >= (present_pages >> 2);
2388 2389
}

2390
/* is kswapd sleeping prematurely? */
2391 2392
static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
					int classzone_idx)
2393
{
2394
	int i;
2395 2396
	unsigned long balanced = 0;
	bool all_zones_ok = true;
2397 2398 2399

	/* If a direct reclaimer woke kswapd within HZ/10, it's premature */
	if (remaining)
2400
		return true;
2401

2402
	/* Check the watermark levels */
2403
	for (i = 0; i <= classzone_idx; i++) {
2404 2405 2406 2407 2408
		struct zone *zone = pgdat->node_zones + i;

		if (!populated_zone(zone))
			continue;

2409 2410 2411 2412 2413 2414 2415 2416
		/*
		 * balance_pgdat() skips over all_unreclaimable after
		 * DEF_PRIORITY. Effectively, it considers them balanced so
		 * they must be considered balanced here as well if kswapd
		 * is to sleep
		 */
		if (zone->all_unreclaimable) {
			balanced += zone->present_pages;
2417
			continue;
2418
		}
2419

2420
		if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone),
2421
							i, 0))
2422 2423 2424
			all_zones_ok = false;
		else
			balanced += zone->present_pages;
2425
	}
2426

2427 2428 2429 2430 2431 2432
	/*
	 * For high-order requests, the balanced zones must contain at least
	 * 25% of the nodes pages for kswapd to sleep. For order-0, all zones
	 * must be balanced
	 */
	if (order)
2433
		return !pgdat_balanced(pgdat, balanced, classzone_idx);
2434 2435
	else
		return !all_zones_ok;
2436 2437
}

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2438 2439
/*
 * For kswapd, balance_pgdat() will work across all this node's zones until
2440
 * they are all at high_wmark_pages(zone).
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2441
 *
2442
 * Returns the final order kswapd was reclaiming at
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 *
 * 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
2453 2454 2455 2456 2457
 * 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.
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 */
2459
static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
2460
							int *classzone_idx)
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2461 2462
{
	int all_zones_ok;
2463
	unsigned long balanced;
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2464 2465
	int priority;
	int i;
2466
	int end_zone = 0;	/* Inclusive.  0 = ZONE_DMA */
2467
	unsigned long total_scanned;
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2468
	struct reclaim_state *reclaim_state = current->reclaim_state;
2469 2470
	unsigned long nr_soft_reclaimed;
	unsigned long nr_soft_scanned;
2471 2472
	struct scan_control sc = {
		.gfp_mask = GFP_KERNEL,
2473
		.may_unmap = 1,
2474
		.may_swap = 1,
2475 2476 2477 2478 2479
		/*
		 * 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,
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2480
		.order = order,
2481
		.target_mem_cgroup = NULL,
2482
	};
2483 2484 2485
	struct shrink_control shrink = {
		.gfp_mask = sc.gfp_mask,
	};
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2486 2487
loop_again:
	total_scanned = 0;
2488
	sc.nr_reclaimed = 0;
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2489
	sc.may_writepage = !laptop_mode;
2490
	count_vm_event(PAGEOUTRUN);
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2491 2492 2493

	for (priority = DEF_PRIORITY; priority >= 0; priority--) {
		unsigned long lru_pages = 0;
2494
		int has_under_min_watermark_zone = 0;
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2495 2496

		all_zones_ok = 1;
2497
		balanced = 0;
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2498

2499 2500 2501 2502 2503 2504
		/*
		 * 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;
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2505

2506 2507
			if (!populated_zone(zone))
				continue;
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2508

2509
			if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2510
				continue;
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2511

2512 2513 2514 2515
			/*
			 * Do some background aging of the anon list, to give
			 * pages a chance to be referenced before reclaiming.
			 */
2516
			age_active_anon(zone, &sc, priority);
2517

2518 2519 2520 2521 2522 2523 2524 2525 2526 2527 2528
			/*
			 * 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;
			}

2529
			if (!zone_watermark_ok_safe(zone, order,
2530
					high_wmark_pages(zone), 0, 0)) {
2531
				end_zone = i;
2532
				break;
2533 2534 2535
			} else {
				/* If balanced, clear the congested flag */
				zone_clear_flag(zone, ZONE_CONGESTED);
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2536 2537
			}
		}
2538 2539 2540
		if (i < 0)
			goto out;

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2541 2542 2543
		for (i = 0; i <= end_zone; i++) {
			struct zone *zone = pgdat->node_zones + i;

2544
			lru_pages += zone_reclaimable_pages(zone);
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2545 2546 2547 2548 2549 2550 2551 2552 2553 2554 2555 2556 2557
		}

		/*
		 * 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;
2558
			int nr_slab, testorder;
2559
			unsigned long balance_gap;
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2560

2561
			if (!populated_zone(zone))
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2562 2563
				continue;

2564
			if (zone->all_unreclaimable && priority != DEF_PRIORITY)
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2565 2566 2567
				continue;

			sc.nr_scanned = 0;
2568

2569
			nr_soft_scanned = 0;
2570 2571 2572
			/*
			 * Call soft limit reclaim before calling shrink_zone.
			 */
2573 2574 2575 2576 2577
			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;
2578

2579
			/*
2580 2581 2582 2583 2584 2585
			 * 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.
2586
			 */
2587 2588 2589 2590
			balance_gap = min(low_wmark_pages(zone),
				(zone->present_pages +
					KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
				KSWAPD_ZONE_BALANCE_GAP_RATIO);
2591 2592 2593 2594 2595 2596 2597 2598 2599 2600 2601 2602 2603
			/*
			 * 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;
			if (COMPACTION_BUILD && order &&
					compaction_suitable(zone, order) !=
						COMPACT_SKIPPED)
				testorder = 0;

2604
			if ((buffer_heads_over_limit && is_highmem_idx(i)) ||
2605
				    !zone_watermark_ok_safe(zone, testorder,
2606
					high_wmark_pages(zone) + balance_gap,
2607
					end_zone, 0)) {
2608
				shrink_zone(priority, zone, &sc);
2609

2610 2611 2612 2613 2614 2615 2616 2617 2618
				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;
			}

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2619 2620 2621 2622 2623 2624
			/*
			 * 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 &&
2625
			    total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
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2626
				sc.may_writepage = 1;
2627

2628 2629 2630
			if (zone->all_unreclaimable) {
				if (end_zone && end_zone == i)
					end_zone--;
2631
				continue;
2632
			}
2633

2634
			if (!zone_watermark_ok_safe(zone, testorder,
2635 2636 2637 2638 2639 2640 2641
					high_wmark_pages(zone), end_zone, 0)) {
				all_zones_ok = 0;
				/*
				 * We are still under min water mark.  This
				 * means that we have a GFP_ATOMIC allocation
				 * failure risk. Hurry up!
				 */
2642
				if (!zone_watermark_ok_safe(zone, order,
2643 2644
					    min_wmark_pages(zone), end_zone, 0))
					has_under_min_watermark_zone = 1;
2645 2646 2647 2648 2649 2650 2651 2652 2653
			} 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,
				 * spectulatively avoid congestion waits
				 */
				zone_clear_flag(zone, ZONE_CONGESTED);
2654
				if (i <= *classzone_idx)
2655
					balanced += zone->present_pages;
2656
			}
2657

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2658
		}
2659
		if (all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))
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2660 2661 2662 2663 2664
			break;		/* kswapd: all done */
		/*
		 * OK, kswapd is getting into trouble.  Take a nap, then take
		 * another pass across the zones.
		 */
2665 2666 2667 2668 2669 2670
		if (total_scanned && (priority < DEF_PRIORITY - 2)) {
			if (has_under_min_watermark_zone)
				count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
			else
				congestion_wait(BLK_RW_ASYNC, HZ/10);
		}
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		/*
		 * 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.
		 */
2678
		if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
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2679 2680 2681
			break;
	}
out:
2682 2683 2684

	/*
	 * order-0: All zones must meet high watermark for a balanced node
2685 2686
	 * high-order: Balanced zones must make up at least 25% of the node
	 *             for the node to be balanced
2687
	 */
2688
	if (!(all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))) {
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2689
		cond_resched();
2690 2691 2692

		try_to_freeze();

2693 2694 2695 2696 2697 2698 2699 2700 2701 2702 2703 2704 2705 2706 2707 2708 2709
		/*
		 * 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;

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		goto loop_again;
	}

2713 2714 2715 2716 2717 2718 2719 2720 2721
	/*
	 * 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) {
2722 2723
		int zones_need_compaction = 1;

2724 2725 2726 2727 2728 2729 2730 2731 2732
		for (i = 0; i <= end_zone; i++) {
			struct zone *zone = pgdat->node_zones + i;

			if (!populated_zone(zone))
				continue;

			if (zone->all_unreclaimable && priority != DEF_PRIORITY)
				continue;

2733
			/* Would compaction fail due to lack of free memory? */
2734 2735
			if (COMPACTION_BUILD &&
			    compaction_suitable(zone, order) == COMPACT_SKIPPED)
2736 2737
				goto loop_again;

2738 2739 2740 2741 2742 2743 2744
			/* Confirm the zone is balanced for order-0 */
			if (!zone_watermark_ok(zone, 0,
					high_wmark_pages(zone), 0, 0)) {
				order = sc.order = 0;
				goto loop_again;
			}

2745 2746 2747 2748 2749
			/* 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;

2750 2751 2752
			/* If balanced, clear the congested flag */
			zone_clear_flag(zone, ZONE_CONGESTED);
		}
2753 2754 2755

		if (zones_need_compaction)
			compact_pgdat(pgdat, order);
2756 2757
	}

2758 2759 2760 2761 2762 2763
	/*
	 * Return the order we were reclaiming at so sleeping_prematurely()
	 * 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
	 */
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	*classzone_idx = end_zone;
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	return order;
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}

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static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
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{
	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 */
2779
	if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
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		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.
	 */
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	if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
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		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);
		schedule();
		set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
	} else {
		if (remaining)
			count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
		else
			count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
	}
	finish_wait(&pgdat->kswapd_wait, &wait);
}

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/*
 * The background pageout daemon, started as a kernel thread
2814
 * from the init process.
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 *
 * 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)
{
2827
	unsigned long order, new_order;
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	unsigned balanced_order;
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	int classzone_idx, new_classzone_idx;
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	int balanced_classzone_idx;
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	pg_data_t *pgdat = (pg_data_t*)p;
	struct task_struct *tsk = current;
2833

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	struct reclaim_state reclaim_state = {
		.reclaimed_slab = 0,
	};
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	const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
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	lockdep_set_current_reclaim_state(GFP_KERNEL);

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	if (!cpumask_empty(cpumask))
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		set_cpus_allowed_ptr(tsk, cpumask);
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	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).
	 */
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	tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
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	set_freezable();
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	order = new_order = 0;
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	balanced_order = 0;
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	classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
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	balanced_classzone_idx = classzone_idx;
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	for ( ; ; ) {
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		int ret;
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		/*
		 * 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
		 */
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		if (balanced_classzone_idx >= new_classzone_idx &&
					balanced_order == new_order) {
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			new_order = pgdat->kswapd_max_order;
			new_classzone_idx = pgdat->classzone_idx;
			pgdat->kswapd_max_order =  0;
			pgdat->classzone_idx = pgdat->nr_zones - 1;
		}

2880
		if (order < new_order || classzone_idx > new_classzone_idx) {
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			/*
			 * Don't sleep if someone wants a larger 'order'
2883
			 * allocation or has tigher zone constraints
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			 */
			order = new_order;
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			classzone_idx = new_classzone_idx;
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		} else {
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			kswapd_try_to_sleep(pgdat, balanced_order,
						balanced_classzone_idx);
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			order = pgdat->kswapd_max_order;
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			classzone_idx = pgdat->classzone_idx;
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			new_order = order;
			new_classzone_idx = classzone_idx;
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			pgdat->kswapd_max_order = 0;
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			pgdat->classzone_idx = pgdat->nr_zones - 1;
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		}

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		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
		 */
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		if (!ret) {
			trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
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			balanced_classzone_idx = classzone_idx;
			balanced_order = balance_pgdat(pgdat, order,
						&balanced_classzone_idx);
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		}
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	}
	return 0;
}

/*
 * A zone is low on free memory, so wake its kswapd task to service it.
 */
2919
void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
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{
	pg_data_t *pgdat;

2923
	if (!populated_zone(zone))
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		return;

2926
	if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
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		return;
2928
	pgdat = zone->zone_pgdat;
2929
	if (pgdat->kswapd_max_order < order) {
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		pgdat->kswapd_max_order = order;
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		pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
	}
2933
	if (!waitqueue_active(&pgdat->kswapd_wait))
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		return;
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	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);
2939
	wake_up_interruptible(&pgdat->kswapd_wait);
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}

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/*
 * 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)
2950
{
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	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;
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}

2977
#ifdef CONFIG_HIBERNATION
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/*
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 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
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 * 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
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 */
2986
unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
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{
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	struct reclaim_state reclaim_state;
	struct scan_control sc = {
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		.gfp_mask = GFP_HIGHUSER_MOVABLE,
		.may_swap = 1,
		.may_unmap = 1,
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		.may_writepage = 1,
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		.nr_to_reclaim = nr_to_reclaim,
		.hibernation_mode = 1,
		.order = 0,
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	};
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	struct shrink_control shrink = {
		.gfp_mask = sc.gfp_mask,
	};
	struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
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	struct task_struct *p = current;
	unsigned long nr_reclaimed;
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	p->flags |= PF_MEMALLOC;
	lockdep_set_current_reclaim_state(sc.gfp_mask);
	reclaim_state.reclaimed_slab = 0;
	p->reclaim_state = &reclaim_state;
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3010
	nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
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	p->reclaim_state = NULL;
	lockdep_clear_current_reclaim_state();
	p->flags &= ~PF_MEMALLOC;
3015

3016
	return nr_reclaimed;
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}
3018
#endif /* CONFIG_HIBERNATION */
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/* 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. */
3024
static int __devinit cpu_callback(struct notifier_block *nfb,
3025
				  unsigned long action, void *hcpu)
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{
3027
	int nid;
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3029
	if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
3030
		for_each_node_state(nid, N_HIGH_MEMORY) {
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			pg_data_t *pgdat = NODE_DATA(nid);
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			const struct cpumask *mask;

			mask = cpumask_of_node(pgdat->node_id);
3035

3036
			if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
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				/* One of our CPUs online: restore mask */
3038
				set_cpus_allowed_ptr(pgdat->kswapd, mask);
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		}
	}
	return NOTIFY_OK;
}

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/*
 * 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);
		printk("Failed to start kswapd on node %d\n",nid);
		ret = -1;
	}
	return ret;
}

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/*
 * Called by memory hotplug when all memory in a node is offlined.
 */
void kswapd_stop(int nid)
{
	struct task_struct *kswapd = NODE_DATA(nid)->kswapd;

	if (kswapd)
		kthread_stop(kswapd);
}

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static int __init kswapd_init(void)
{
3079
	int nid;
3080

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	swap_setup();
3082
	for_each_node_state(nid, N_HIGH_MEMORY)
3083
 		kswapd_run(nid);
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	hotcpu_notifier(cpu_callback, 0);
	return 0;
}

module_init(kswapd_init)
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#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;

3099
#define RECLAIM_OFF 0
3100
#define RECLAIM_ZONE (1<<0)	/* Run shrink_inactive_list on the zone */
3101 3102 3103
#define RECLAIM_WRITE (1<<1)	/* Writeout pages during reclaim */
#define RECLAIM_SWAP (1<<2)	/* Swap pages out during reclaim */

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/*
 * 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

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/*
 * Percentage of pages in a zone that must be unmapped for zone_reclaim to
 * occur.
 */
int sysctl_min_unmapped_ratio = 1;

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/*
 * 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;

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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;
}

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/*
 * Try to free up some pages from this zone through reclaim.
 */
3168
static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3169
{
3170
	/* Minimum pages needed in order to stay on node */
3171
	const unsigned long nr_pages = 1 << order;
3172 3173
	struct task_struct *p = current;
	struct reclaim_state reclaim_state;
3174
	int priority;
3175 3176
	struct scan_control sc = {
		.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
3177
		.may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
3178
		.may_swap = 1,
3179 3180
		.nr_to_reclaim = max_t(unsigned long, nr_pages,
				       SWAP_CLUSTER_MAX),
3181
		.gfp_mask = gfp_mask,
3182
		.order = order,
3183
	};
3184 3185 3186
	struct shrink_control shrink = {
		.gfp_mask = sc.gfp_mask,
	};
3187
	unsigned long nr_slab_pages0, nr_slab_pages1;
3188 3189

	cond_resched();
3190 3191 3192 3193 3194 3195
	/*
	 * 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;
3196
	lockdep_set_current_reclaim_state(gfp_mask);
3197 3198
	reclaim_state.reclaimed_slab = 0;
	p->reclaim_state = &reclaim_state;
3199

3200
	if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
3201 3202 3203 3204 3205 3206
		/*
		 * Free memory by calling shrink zone with increasing
		 * priorities until we have enough memory freed.
		 */
		priority = ZONE_RECLAIM_PRIORITY;
		do {
3207
			shrink_zone(priority, zone, &sc);
3208
			priority--;
3209
		} while (priority >= 0 && sc.nr_reclaimed < nr_pages);
3210
	}
3211

3212 3213
	nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
	if (nr_slab_pages0 > zone->min_slab_pages) {
3214
		/*
3215
		 * shrink_slab() does not currently allow us to determine how
3216 3217 3218 3219
		 * 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.
3220
		 *
3221 3222
		 * Note that shrink_slab will free memory on all zones and may
		 * take a long time.
3223
		 */
3224 3225 3226 3227
		for (;;) {
			unsigned long lru_pages = zone_reclaimable_pages(zone);

			/* No reclaimable slab or very low memory pressure */
3228
			if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages))
3229 3230 3231 3232 3233 3234 3235 3236
				break;

			/* Freed enough memory */
			nr_slab_pages1 = zone_page_state(zone,
							NR_SLAB_RECLAIMABLE);
			if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
				break;
		}
3237 3238 3239 3240 3241

		/*
		 * Update nr_reclaimed by the number of slab pages we
		 * reclaimed from this zone.
		 */
3242 3243 3244
		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;
3245 3246
	}

3247
	p->reclaim_state = NULL;
3248
	current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
3249
	lockdep_clear_current_reclaim_state();
3250
	return sc.nr_reclaimed >= nr_pages;
3251
}
3252 3253 3254 3255

int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
{
	int node_id;
3256
	int ret;
3257 3258

	/*
3259 3260
	 * Zone reclaim reclaims unmapped file backed pages and
	 * slab pages if we are over the defined limits.
3261
	 *
3262 3263 3264 3265 3266
	 * 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.
3267
	 */
3268 3269
	if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
	    zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
3270
		return ZONE_RECLAIM_FULL;
3271

3272
	if (zone->all_unreclaimable)
3273
		return ZONE_RECLAIM_FULL;
3274

3275
	/*
3276
	 * Do not scan if the allocation should not be delayed.
3277
	 */
3278
	if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
3279
		return ZONE_RECLAIM_NOSCAN;
3280 3281 3282 3283 3284 3285 3286

	/*
	 * 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.
	 */
3287
	node_id = zone_to_nid(zone);
3288
	if (node_state(node_id, N_CPU) && node_id != numa_node_id())
3289
		return ZONE_RECLAIM_NOSCAN;
3290 3291

	if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
3292 3293
		return ZONE_RECLAIM_NOSCAN;

3294 3295 3296
	ret = __zone_reclaim(zone, gfp_mask, order);
	zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);

3297 3298 3299
	if (!ret)
		count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);

3300
	return ret;
3301
}
3302
#endif
3303 3304 3305 3306 3307 3308 3309

/*
 * page_evictable - test whether a page is evictable
 * @page: the page to test
 * @vma: the VMA in which the page is or will be mapped, may be NULL
 *
 * Test whether page is evictable--i.e., should be placed on active/inactive
3310 3311
 * lists vs unevictable list.  The vma argument is !NULL when called from the
 * fault path to determine how to instantate a new page.
3312 3313
 *
 * Reasons page might not be evictable:
3314
 * (1) page's mapping marked unevictable
3315
 * (2) page is part of an mlocked VMA
3316
 *
3317 3318 3319 3320
 */
int page_evictable(struct page *page, struct vm_area_struct *vma)
{

3321 3322 3323
	if (mapping_unevictable(page_mapping(page)))
		return 0;

3324
	if (PageMlocked(page) || (vma && mlocked_vma_newpage(vma, page)))
3325
		return 0;
3326 3327 3328

	return 1;
}
3329

3330
#ifdef CONFIG_SHMEM
3331
/**
3332 3333 3334
 * 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
3335
 *
3336
 * Checks pages for evictability and moves them to the appropriate lru list.
3337 3338
 *
 * This function is only used for SysV IPC SHM_UNLOCK.
3339
 */
3340
void check_move_unevictable_pages(struct page **pages, int nr_pages)
3341
{
3342
	struct lruvec *lruvec;
3343 3344 3345 3346
	struct zone *zone = NULL;
	int pgscanned = 0;
	int pgrescued = 0;
	int i;
3347

3348 3349 3350
	for (i = 0; i < nr_pages; i++) {
		struct page *page = pages[i];
		struct zone *pagezone;
3351

3352 3353 3354 3355 3356 3357 3358 3359
		pgscanned++;
		pagezone = page_zone(page);
		if (pagezone != zone) {
			if (zone)
				spin_unlock_irq(&zone->lru_lock);
			zone = pagezone;
			spin_lock_irq(&zone->lru_lock);
		}
3360

3361 3362
		if (!PageLRU(page) || !PageUnevictable(page))
			continue;
3363

3364 3365 3366 3367 3368 3369 3370 3371 3372 3373 3374
		if (page_evictable(page, NULL)) {
			enum lru_list lru = page_lru_base_type(page);

			VM_BUG_ON(PageActive(page));
			ClearPageUnevictable(page);
			__dec_zone_state(zone, NR_UNEVICTABLE);
			lruvec = mem_cgroup_lru_move_lists(zone, page,
						LRU_UNEVICTABLE, lru);
			list_move(&page->lru, &lruvec->lists[lru]);
			__inc_zone_state(zone, NR_INACTIVE_ANON + lru);
			pgrescued++;
3375
		}
3376
	}
3377

3378 3379 3380 3381
	if (zone) {
		__count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
		__count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
		spin_unlock_irq(&zone->lru_lock);
3382 3383
	}
}
3384
#endif /* CONFIG_SHMEM */
3385

3386
static void warn_scan_unevictable_pages(void)
3387
{
3388
	printk_once(KERN_WARNING
3389
		    "%s: The scan_unevictable_pages sysctl/node-interface has been "
3390
		    "disabled for lack of a legitimate use case.  If you have "
3391 3392
		    "one, please send an email to linux-mm@kvack.org.\n",
		    current->comm);
3393 3394 3395 3396 3397 3398 3399 3400 3401
}

/*
 * 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,
3402
			   void __user *buffer,
3403 3404
			   size_t *length, loff_t *ppos)
{
3405
	warn_scan_unevictable_pages();
3406
	proc_doulongvec_minmax(table, write, buffer, length, ppos);
3407 3408 3409 3410
	scan_unevictable_pages = 0;
	return 0;
}

3411
#ifdef CONFIG_NUMA
3412 3413 3414 3415 3416
/*
 * per node 'scan_unevictable_pages' attribute.  On demand re-scan of
 * a specified node's per zone unevictable lists for evictable pages.
 */

3417 3418
static ssize_t read_scan_unevictable_node(struct device *dev,
					  struct device_attribute *attr,
3419 3420
					  char *buf)
{
3421
	warn_scan_unevictable_pages();
3422 3423 3424
	return sprintf(buf, "0\n");	/* always zero; should fit... */
}

3425 3426
static ssize_t write_scan_unevictable_node(struct device *dev,
					   struct device_attribute *attr,
3427 3428
					const char *buf, size_t count)
{
3429
	warn_scan_unevictable_pages();
3430 3431 3432 3433
	return 1;
}


3434
static DEVICE_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
3435 3436 3437 3438 3439
			read_scan_unevictable_node,
			write_scan_unevictable_node);

int scan_unevictable_register_node(struct node *node)
{
3440
	return device_create_file(&node->dev, &dev_attr_scan_unevictable_pages);
3441 3442 3443 3444
}

void scan_unevictable_unregister_node(struct node *node)
{
3445
	device_remove_file(&node->dev, &dev_attr_scan_unevictable_pages);
3446
}
3447
#endif