vmscan.c 44.1 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>
#include <linux/slab.h>
#include <linux/kernel_stat.h>
#include <linux/swap.h>
#include <linux/pagemap.h>
#include <linux/init.h>
#include <linux/highmem.h>
#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/pagevec.h>
#include <linux/backing-dev.h>
#include <linux/rmap.h>
#include <linux/topology.h>
#include <linux/cpu.h>
#include <linux/cpuset.h>
#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 <asm/tlbflush.h>
#include <asm/div64.h>

#include <linux/swapops.h>

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#include "internal.h"

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struct scan_control {
	/* Incremented by the number of inactive pages that were scanned */
	unsigned long nr_scanned;

	unsigned long nr_mapped;	/* From page_state */

	/* 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 pages be swapped as part of reclaim? */
	int may_swap;

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	/* This context's SWAP_CLUSTER_MAX. If freeing memory for
	 * suspend, we effectively ignore SWAP_CLUSTER_MAX.
	 * In this context, it doesn't matter that we scan the
	 * whole list at once. */
	int swap_cluster_max;
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	int swappiness;
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};

/*
 * The list of shrinker callbacks used by to apply pressure to
 * ageable caches.
 */
struct shrinker {
	shrinker_t		shrinker;
	struct list_head	list;
	int			seeks;	/* seeks to recreate an obj */
	long			nr;	/* objs pending delete */
};

#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);

/*
 * Add a shrinker callback to be called from the vm
 */
struct shrinker *set_shrinker(int seeks, shrinker_t theshrinker)
{
        struct shrinker *shrinker;

        shrinker = kmalloc(sizeof(*shrinker), GFP_KERNEL);
        if (shrinker) {
	        shrinker->shrinker = theshrinker;
	        shrinker->seeks = seeks;
	        shrinker->nr = 0;
	        down_write(&shrinker_rwsem);
	        list_add_tail(&shrinker->list, &shrinker_list);
	        up_write(&shrinker_rwsem);
	}
	return shrinker;
}
EXPORT_SYMBOL(set_shrinker);

/*
 * Remove one
 */
void remove_shrinker(struct shrinker *shrinker)
{
	down_write(&shrinker_rwsem);
	list_del(&shrinker->list);
	up_write(&shrinker_rwsem);
	kfree(shrinker);
}
EXPORT_SYMBOL(remove_shrinker);

#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.
 *
 * If the vm encounted mapped pages on the LRU it increase the pressure on
 * 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(unsigned long scanned, gfp_t gfp_mask,
			unsigned long lru_pages)
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{
	struct shrinker *shrinker;
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	unsigned long ret = 0;
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	if (scanned == 0)
		scanned = SWAP_CLUSTER_MAX;

	if (!down_read_trylock(&shrinker_rwsem))
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		return 1;	/* Assume we'll be able to shrink next time */
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	list_for_each_entry(shrinker, &shrinker_list, list) {
		unsigned long long delta;
		unsigned long total_scan;
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		unsigned long max_pass = (*shrinker->shrinker)(0, gfp_mask);
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		delta = (4 * scanned) / shrinker->seeks;
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		delta *= max_pass;
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		do_div(delta, lru_pages + 1);
		shrinker->nr += delta;
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		if (shrinker->nr < 0) {
			printk(KERN_ERR "%s: nr=%ld\n",
					__FUNCTION__, shrinker->nr);
			shrinker->nr = max_pass;
		}

		/*
		 * Avoid risking looping forever due to too large nr value:
		 * never try to free more than twice the estimate number of
		 * freeable entries.
		 */
		if (shrinker->nr > max_pass * 2)
			shrinker->nr = max_pass * 2;
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		total_scan = shrinker->nr;
		shrinker->nr = 0;

		while (total_scan >= SHRINK_BATCH) {
			long this_scan = SHRINK_BATCH;
			int shrink_ret;
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			int nr_before;
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			nr_before = (*shrinker->shrinker)(0, gfp_mask);
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			shrink_ret = (*shrinker->shrinker)(this_scan, gfp_mask);
			if (shrink_ret == -1)
				break;
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			if (shrink_ret < nr_before)
				ret += nr_before - shrink_ret;
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			mod_page_state(slabs_scanned, this_scan);
			total_scan -= this_scan;

			cond_resched();
		}

		shrinker->nr += total_scan;
	}
	up_read(&shrinker_rwsem);
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	return ret;
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}

/* Called without lock on whether page is mapped, so answer is unstable */
static inline int page_mapping_inuse(struct page *page)
{
	struct address_space *mapping;

	/* Page is in somebody's page tables. */
	if (page_mapped(page))
		return 1;

	/* Be more reluctant to reclaim swapcache than pagecache */
	if (PageSwapCache(page))
		return 1;

	mapping = page_mapping(page);
	if (!mapping)
		return 0;

	/* File is mmap'd by somebody? */
	return mapping_mapped(mapping);
}

static inline int is_page_cache_freeable(struct page *page)
{
	return page_count(page) - !!PagePrivate(page) == 2;
}

static int may_write_to_queue(struct backing_dev_info *bdi)
{
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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)
{
	lock_page(page);
	if (page_mapping(page) == mapping) {
		if (error == -ENOSPC)
			set_bit(AS_ENOSPC, &mapping->flags);
		else
			set_bit(AS_EIO, &mapping->flags);
	}
	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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{
	/*
	 * 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.
	 *
	 * If this process is currently in generic_file_write() against
	 * 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.
	 * See swapfile.c:page_queue_congested().
	 */
	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 (PagePrivate(page)) {
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			if (try_to_free_buffers(page)) {
				ClearPageDirty(page);
				printk("%s: orphaned page\n", __FUNCTION__);
				return PAGE_CLEAN;
			}
		}
		return PAGE_KEEP;
	}
	if (mapping->a_ops->writepage == NULL)
		return PAGE_ACTIVATE;
	if (!may_write_to_queue(mapping->backing_dev_info))
		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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			.nonblocking = 1,
			.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;
		}
		if (!PageWriteback(page)) {
			/* synchronous write or broken a_ops? */
			ClearPageReclaim(page);
		}

		return PAGE_SUCCESS;
	}

	return PAGE_CLEAN;
}

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int remove_mapping(struct address_space *mapping, struct page *page)
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{
	if (!mapping)
		return 0;		/* truncate got there first */

	write_lock_irq(&mapping->tree_lock);

	/*
	 * The non-racy check for busy page.  It is critical to check
	 * PageDirty _after_ making sure that the page is freeable and
	 * not in use by anybody. 	(pagecache + us == 2)
	 */
	if (unlikely(page_count(page) != 2))
		goto cannot_free;
	smp_rmb();
	if (unlikely(PageDirty(page)))
		goto cannot_free;

	if (PageSwapCache(page)) {
		swp_entry_t swap = { .val = page_private(page) };
		__delete_from_swap_cache(page);
		write_unlock_irq(&mapping->tree_lock);
		swap_free(swap);
		__put_page(page);	/* The pagecache ref */
		return 1;
	}

	__remove_from_page_cache(page);
	write_unlock_irq(&mapping->tree_lock);
	__put_page(page);
	return 1;

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

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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,
					struct scan_control *sc)
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{
	LIST_HEAD(ret_pages);
	struct pagevec freed_pvec;
	int pgactivate = 0;
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	unsigned long nr_reclaimed = 0;
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	cond_resched();

	pagevec_init(&freed_pvec, 1);
	while (!list_empty(page_list)) {
		struct address_space *mapping;
		struct page *page;
		int may_enter_fs;
		int referenced;

		cond_resched();

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

		if (TestSetPageLocked(page))
			goto keep;

		BUG_ON(PageActive(page));

		sc->nr_scanned++;
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		if (!sc->may_swap && page_mapped(page))
			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++;

		if (PageWriteback(page))
			goto keep_locked;

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		referenced = page_referenced(page, 1);
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		/* In active use or really unfreeable?  Activate it. */
		if (referenced && page_mapping_inuse(page))
			goto activate_locked;

#ifdef CONFIG_SWAP
		/*
		 * 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 (!add_to_swap(page, GFP_ATOMIC))
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				goto activate_locked;
#endif /* CONFIG_SWAP */

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

		/*
		 * 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, 0)) {
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			case SWAP_FAIL:
				goto activate_locked;
			case SWAP_AGAIN:
				goto keep_locked;
			case SWAP_SUCCESS:
				; /* try to free the page below */
			}
		}

		if (PageDirty(page)) {
			if (referenced)
				goto keep_locked;
			if (!may_enter_fs)
				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 */
			switch(pageout(page, mapping)) {
			case PAGE_KEEP:
				goto keep_locked;
			case PAGE_ACTIVATE:
				goto activate_locked;
			case PAGE_SUCCESS:
				if (PageWriteback(page) || PageDirty(page))
					goto keep;
				/*
				 * A synchronous write - probably a ramdisk.  Go
				 * ahead and try to reclaim the page.
				 */
				if (TestSetPageLocked(page))
					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
		 * will do this, as well as the blockdev mapping. 
		 * 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.
		 */
		if (PagePrivate(page)) {
			if (!try_to_release_page(page, sc->gfp_mask))
				goto activate_locked;
			if (!mapping && page_count(page) == 1)
				goto free_it;
		}

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		if (!remove_mapping(mapping, page))
			goto keep_locked;
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free_it:
		unlock_page(page);
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		nr_reclaimed++;
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		if (!pagevec_add(&freed_pvec, page))
			__pagevec_release_nonlru(&freed_pvec);
		continue;

activate_locked:
		SetPageActive(page);
		pgactivate++;
keep_locked:
		unlock_page(page);
keep:
		list_add(&page->lru, &ret_pages);
		BUG_ON(PageLRU(page));
	}
	list_splice(&ret_pages, page_list);
	if (pagevec_count(&freed_pvec))
		__pagevec_release_nonlru(&freed_pvec);
	mod_page_state(pgactivate, pgactivate);
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	return nr_reclaimed;
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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.
 * @src:	The LRU list to pull pages off.
 * @dst:	The temp list to put pages on to.
 * @scanned:	The number of pages that were scanned.
 *
 * returns how many pages were moved onto *@dst.
 */
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static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
		struct list_head *src, struct list_head *dst,
		unsigned long *scanned)
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{
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	unsigned long nr_taken = 0;
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	struct page *page;
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	unsigned long scan;
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	for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
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		struct list_head *target;
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		page = lru_to_page(src);
		prefetchw_prev_lru_page(page, src, flags);

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		BUG_ON(!PageLRU(page));

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		list_del(&page->lru);
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		target = src;
		if (likely(get_page_unless_zero(page))) {
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			/*
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			 * 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.
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			 */
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			ClearPageLRU(page);
			target = dst;
			nr_taken++;
		} /* else it is being freed elsewhere */
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		list_add(&page->lru, target);
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	}

	*scanned = scan;
	return nr_taken;
}

/*
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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 unsigned long shrink_inactive_list(unsigned long max_scan,
				struct zone *zone, struct scan_control *sc)
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{
	LIST_HEAD(page_list);
	struct pagevec pvec;
639
	unsigned long nr_scanned = 0;
640
	unsigned long nr_reclaimed = 0;
L
Linus Torvalds 已提交
641 642 643 644 645

	pagevec_init(&pvec, 1);

	lru_add_drain();
	spin_lock_irq(&zone->lru_lock);
646
	do {
L
Linus Torvalds 已提交
647
		struct page *page;
648 649 650
		unsigned long nr_taken;
		unsigned long nr_scan;
		unsigned long nr_freed;
L
Linus Torvalds 已提交
651 652 653 654 655 656 657 658

		nr_taken = isolate_lru_pages(sc->swap_cluster_max,
					     &zone->inactive_list,
					     &page_list, &nr_scan);
		zone->nr_inactive -= nr_taken;
		zone->pages_scanned += nr_scan;
		spin_unlock_irq(&zone->lru_lock);

659
		nr_scanned += nr_scan;
A
Andrew Morton 已提交
660
		nr_freed = shrink_page_list(&page_list, sc);
661
		nr_reclaimed += nr_freed;
N
Nick Piggin 已提交
662 663 664 665 666 667 668 669
		local_irq_disable();
		if (current_is_kswapd()) {
			__mod_page_state_zone(zone, pgscan_kswapd, nr_scan);
			__mod_page_state(kswapd_steal, nr_freed);
		} else
			__mod_page_state_zone(zone, pgscan_direct, nr_scan);
		__mod_page_state_zone(zone, pgsteal, nr_freed);

670 671 672
		if (nr_taken == 0)
			goto done;

N
Nick Piggin 已提交
673
		spin_lock(&zone->lru_lock);
L
Linus Torvalds 已提交
674 675 676 677 678
		/*
		 * Put back any unfreeable pages.
		 */
		while (!list_empty(&page_list)) {
			page = lru_to_page(&page_list);
N
Nick Piggin 已提交
679 680
			BUG_ON(PageLRU(page));
			SetPageLRU(page);
L
Linus Torvalds 已提交
681 682 683 684 685 686 687 688 689 690 691
			list_del(&page->lru);
			if (PageActive(page))
				add_page_to_active_list(zone, page);
			else
				add_page_to_inactive_list(zone, page);
			if (!pagevec_add(&pvec, page)) {
				spin_unlock_irq(&zone->lru_lock);
				__pagevec_release(&pvec);
				spin_lock_irq(&zone->lru_lock);
			}
		}
692
  	} while (nr_scanned < max_scan);
693
	spin_unlock(&zone->lru_lock);
L
Linus Torvalds 已提交
694
done:
695
	local_irq_enable();
L
Linus Torvalds 已提交
696
	pagevec_release(&pvec);
697
	return nr_reclaimed;
L
Linus Torvalds 已提交
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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.
 */
A
Andrew Morton 已提交
717 718
static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
				struct scan_control *sc)
L
Linus Torvalds 已提交
719
{
720
	unsigned long pgmoved;
L
Linus Torvalds 已提交
721
	int pgdeactivate = 0;
722
	unsigned long pgscanned;
L
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723 724 725 726 727 728
	LIST_HEAD(l_hold);	/* The pages which were snipped off */
	LIST_HEAD(l_inactive);	/* Pages to go onto the inactive_list */
	LIST_HEAD(l_active);	/* Pages to go onto the active_list */
	struct page *page;
	struct pagevec pvec;
	int reclaim_mapped = 0;
729

730
	if (sc->may_swap) {
731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746
		long mapped_ratio;
		long distress;
		long swap_tendency;

		/*
		 * `distress' is a measure of how much trouble we're having
		 * reclaiming pages.  0 -> no problems.  100 -> great trouble.
		 */
		distress = 100 >> zone->prev_priority;

		/*
		 * The point of this algorithm is to decide when to start
		 * reclaiming mapped memory instead of just pagecache.  Work out
		 * how much memory
		 * is mapped.
		 */
747
		mapped_ratio = (sc->nr_mapped * 100) / vm_total_pages;
748 749 750 751 752 753 754 755 756 757 758 759 760

		/*
		 * Now decide how much we really want to unmap some pages.  The
		 * mapped ratio is downgraded - just because there's a lot of
		 * mapped memory doesn't necessarily mean that page reclaim
		 * isn't succeeding.
		 *
		 * The distress ratio is important - we don't want to start
		 * going oom.
		 *
		 * A 100% value of vm_swappiness overrides this algorithm
		 * altogether.
		 */
761
		swap_tendency = mapped_ratio / 2 + distress + sc->swappiness;
762 763 764 765 766 767 768 769

		/*
		 * Now use this metric to decide whether to start moving mapped
		 * memory onto the inactive list.
		 */
		if (swap_tendency >= 100)
			reclaim_mapped = 1;
	}
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770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785

	lru_add_drain();
	spin_lock_irq(&zone->lru_lock);
	pgmoved = isolate_lru_pages(nr_pages, &zone->active_list,
				    &l_hold, &pgscanned);
	zone->pages_scanned += pgscanned;
	zone->nr_active -= pgmoved;
	spin_unlock_irq(&zone->lru_lock);

	while (!list_empty(&l_hold)) {
		cond_resched();
		page = lru_to_page(&l_hold);
		list_del(&page->lru);
		if (page_mapped(page)) {
			if (!reclaim_mapped ||
			    (total_swap_pages == 0 && PageAnon(page)) ||
786
			    page_referenced(page, 0)) {
L
Linus Torvalds 已提交
787 788 789 790 791 792 793 794 795 796 797 798 799
				list_add(&page->lru, &l_active);
				continue;
			}
		}
		list_add(&page->lru, &l_inactive);
	}

	pagevec_init(&pvec, 1);
	pgmoved = 0;
	spin_lock_irq(&zone->lru_lock);
	while (!list_empty(&l_inactive)) {
		page = lru_to_page(&l_inactive);
		prefetchw_prev_lru_page(page, &l_inactive, flags);
N
Nick Piggin 已提交
800 801
		BUG_ON(PageLRU(page));
		SetPageLRU(page);
N
Nick Piggin 已提交
802 803 804
		BUG_ON(!PageActive(page));
		ClearPageActive(page);

L
Linus Torvalds 已提交
805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829
		list_move(&page->lru, &zone->inactive_list);
		pgmoved++;
		if (!pagevec_add(&pvec, page)) {
			zone->nr_inactive += pgmoved;
			spin_unlock_irq(&zone->lru_lock);
			pgdeactivate += pgmoved;
			pgmoved = 0;
			if (buffer_heads_over_limit)
				pagevec_strip(&pvec);
			__pagevec_release(&pvec);
			spin_lock_irq(&zone->lru_lock);
		}
	}
	zone->nr_inactive += pgmoved;
	pgdeactivate += pgmoved;
	if (buffer_heads_over_limit) {
		spin_unlock_irq(&zone->lru_lock);
		pagevec_strip(&pvec);
		spin_lock_irq(&zone->lru_lock);
	}

	pgmoved = 0;
	while (!list_empty(&l_active)) {
		page = lru_to_page(&l_active);
		prefetchw_prev_lru_page(page, &l_active, flags);
N
Nick Piggin 已提交
830 831
		BUG_ON(PageLRU(page));
		SetPageLRU(page);
L
Linus Torvalds 已提交
832 833 834 835 836 837 838 839 840 841 842 843
		BUG_ON(!PageActive(page));
		list_move(&page->lru, &zone->active_list);
		pgmoved++;
		if (!pagevec_add(&pvec, page)) {
			zone->nr_active += pgmoved;
			pgmoved = 0;
			spin_unlock_irq(&zone->lru_lock);
			__pagevec_release(&pvec);
			spin_lock_irq(&zone->lru_lock);
		}
	}
	zone->nr_active += pgmoved;
N
Nick Piggin 已提交
844 845 846 847 848
	spin_unlock(&zone->lru_lock);

	__mod_page_state_zone(zone, pgrefill, pgscanned);
	__mod_page_state(pgdeactivate, pgdeactivate);
	local_irq_enable();
L
Linus Torvalds 已提交
849

N
Nick Piggin 已提交
850
	pagevec_release(&pvec);
L
Linus Torvalds 已提交
851 852 853 854 855
}

/*
 * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
 */
856 857
static unsigned long shrink_zone(int priority, struct zone *zone,
				struct scan_control *sc)
L
Linus Torvalds 已提交
858 859 860
{
	unsigned long nr_active;
	unsigned long nr_inactive;
861
	unsigned long nr_to_scan;
862
	unsigned long nr_reclaimed = 0;
L
Linus Torvalds 已提交
863

864 865
	atomic_inc(&zone->reclaim_in_progress);

L
Linus Torvalds 已提交
866 867 868 869
	/*
	 * Add one to `nr_to_scan' just to make sure that the kernel will
	 * slowly sift through the active list.
	 */
870
	zone->nr_scan_active += (zone->nr_active >> priority) + 1;
L
Linus Torvalds 已提交
871 872 873 874 875 876
	nr_active = zone->nr_scan_active;
	if (nr_active >= sc->swap_cluster_max)
		zone->nr_scan_active = 0;
	else
		nr_active = 0;

877
	zone->nr_scan_inactive += (zone->nr_inactive >> priority) + 1;
L
Linus Torvalds 已提交
878 879 880 881 882 883 884 885
	nr_inactive = zone->nr_scan_inactive;
	if (nr_inactive >= sc->swap_cluster_max)
		zone->nr_scan_inactive = 0;
	else
		nr_inactive = 0;

	while (nr_active || nr_inactive) {
		if (nr_active) {
886
			nr_to_scan = min(nr_active,
L
Linus Torvalds 已提交
887
					(unsigned long)sc->swap_cluster_max);
888
			nr_active -= nr_to_scan;
A
Andrew Morton 已提交
889
			shrink_active_list(nr_to_scan, zone, sc);
L
Linus Torvalds 已提交
890 891 892
		}

		if (nr_inactive) {
893
			nr_to_scan = min(nr_inactive,
L
Linus Torvalds 已提交
894
					(unsigned long)sc->swap_cluster_max);
895
			nr_inactive -= nr_to_scan;
A
Andrew Morton 已提交
896 897
			nr_reclaimed += shrink_inactive_list(nr_to_scan, zone,
								sc);
L
Linus Torvalds 已提交
898 899 900 901
		}
	}

	throttle_vm_writeout();
902 903

	atomic_dec(&zone->reclaim_in_progress);
904
	return nr_reclaimed;
L
Linus Torvalds 已提交
905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922
}

/*
 * 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.
 *
 * We reclaim from a zone even if that zone is over pages_high.  Because:
 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
 *    allocation or
 * b) The zones may be over pages_high but they must go *over* pages_high to
 *    satisfy the `incremental min' zone defense algorithm.
 *
 * Returns the number of reclaimed pages.
 *
 * If a zone is deemed to be full of pinned pages then just give it a light
 * scan then give up on it.
 */
A
Andrew Morton 已提交
923
static unsigned long shrink_zones(int priority, struct zone **zones,
924
					struct scan_control *sc)
L
Linus Torvalds 已提交
925
{
926
	unsigned long nr_reclaimed = 0;
L
Linus Torvalds 已提交
927 928 929 930 931
	int i;

	for (i = 0; zones[i] != NULL; i++) {
		struct zone *zone = zones[i];

932
		if (!populated_zone(zone))
L
Linus Torvalds 已提交
933 934
			continue;

935
		if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
L
Linus Torvalds 已提交
936 937
			continue;

938 939 940
		zone->temp_priority = priority;
		if (zone->prev_priority > priority)
			zone->prev_priority = priority;
L
Linus Torvalds 已提交
941

942
		if (zone->all_unreclaimable && priority != DEF_PRIORITY)
L
Linus Torvalds 已提交
943 944
			continue;	/* Let kswapd poll it */

945
		nr_reclaimed += shrink_zone(priority, zone, sc);
L
Linus Torvalds 已提交
946
	}
947
	return nr_reclaimed;
L
Linus Torvalds 已提交
948 949 950 951 952 953 954 955 956 957 958 959 960 961 962
}
 
/*
 * 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
 * caller can't do much about.  We kick pdflush 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.
 */
963
unsigned long try_to_free_pages(struct zone **zones, gfp_t gfp_mask)
L
Linus Torvalds 已提交
964 965 966
{
	int priority;
	int ret = 0;
967
	unsigned long total_scanned = 0;
968
	unsigned long nr_reclaimed = 0;
L
Linus Torvalds 已提交
969 970 971
	struct reclaim_state *reclaim_state = current->reclaim_state;
	unsigned long lru_pages = 0;
	int i;
972 973 974 975 976
	struct scan_control sc = {
		.gfp_mask = gfp_mask,
		.may_writepage = !laptop_mode,
		.swap_cluster_max = SWAP_CLUSTER_MAX,
		.may_swap = 1,
977
		.swappiness = vm_swappiness,
978
	};
L
Linus Torvalds 已提交
979 980 981 982 983 984

	inc_page_state(allocstall);

	for (i = 0; zones[i] != NULL; i++) {
		struct zone *zone = zones[i];

985
		if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
L
Linus Torvalds 已提交
986 987 988 989 990 991 992 993 994
			continue;

		zone->temp_priority = DEF_PRIORITY;
		lru_pages += zone->nr_active + zone->nr_inactive;
	}

	for (priority = DEF_PRIORITY; priority >= 0; priority--) {
		sc.nr_mapped = read_page_state(nr_mapped);
		sc.nr_scanned = 0;
995 996
		if (!priority)
			disable_swap_token();
A
Andrew Morton 已提交
997
		nr_reclaimed += shrink_zones(priority, zones, &sc);
L
Linus Torvalds 已提交
998 999
		shrink_slab(sc.nr_scanned, gfp_mask, lru_pages);
		if (reclaim_state) {
1000
			nr_reclaimed += reclaim_state->reclaimed_slab;
L
Linus Torvalds 已提交
1001 1002 1003
			reclaim_state->reclaimed_slab = 0;
		}
		total_scanned += sc.nr_scanned;
1004
		if (nr_reclaimed >= sc.swap_cluster_max) {
L
Linus Torvalds 已提交
1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015
			ret = 1;
			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.
		 */
1016 1017
		if (total_scanned > sc.swap_cluster_max +
					sc.swap_cluster_max / 2) {
1018
			wakeup_pdflush(laptop_mode ? 0 : total_scanned);
L
Linus Torvalds 已提交
1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029
			sc.may_writepage = 1;
		}

		/* Take a nap, wait for some writeback to complete */
		if (sc.nr_scanned && priority < DEF_PRIORITY - 2)
			blk_congestion_wait(WRITE, HZ/10);
	}
out:
	for (i = 0; zones[i] != 0; i++) {
		struct zone *zone = zones[i];

1030
		if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
L
Linus Torvalds 已提交
1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058
			continue;

		zone->prev_priority = zone->temp_priority;
	}
	return ret;
}

/*
 * For kswapd, balance_pgdat() will work across all this node's zones until
 * they are all at pages_high.
 *
 * Returns the number of pages which were actually freed.
 *
 * 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
 * zones which have free_pages > pages_high, but once a zone is found to have
 * free_pages <= pages_high, 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.
 */
1059
static unsigned long balance_pgdat(pg_data_t *pgdat, int order)
L
Linus Torvalds 已提交
1060 1061 1062 1063
{
	int all_zones_ok;
	int priority;
	int i;
1064
	unsigned long total_scanned;
1065
	unsigned long nr_reclaimed;
L
Linus Torvalds 已提交
1066
	struct reclaim_state *reclaim_state = current->reclaim_state;
1067 1068 1069
	struct scan_control sc = {
		.gfp_mask = GFP_KERNEL,
		.may_swap = 1,
1070 1071
		.swap_cluster_max = SWAP_CLUSTER_MAX,
		.swappiness = vm_swappiness,
1072
	};
L
Linus Torvalds 已提交
1073 1074 1075

loop_again:
	total_scanned = 0;
1076
	nr_reclaimed = 0;
C
Christoph Lameter 已提交
1077
	sc.may_writepage = !laptop_mode;
L
Linus Torvalds 已提交
1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091
	sc.nr_mapped = read_page_state(nr_mapped);

	inc_page_state(pageoutrun);

	for (i = 0; i < pgdat->nr_zones; i++) {
		struct zone *zone = pgdat->node_zones + i;

		zone->temp_priority = DEF_PRIORITY;
	}

	for (priority = DEF_PRIORITY; priority >= 0; priority--) {
		int end_zone = 0;	/* Inclusive.  0 = ZONE_DMA */
		unsigned long lru_pages = 0;

1092 1093 1094 1095
		/* The swap token gets in the way of swapout... */
		if (!priority)
			disable_swap_token();

L
Linus Torvalds 已提交
1096 1097
		all_zones_ok = 1;

1098 1099 1100 1101 1102 1103
		/*
		 * Scan in the highmem->dma direction for the highest
		 * zone which needs scanning
		 */
		for (i = pgdat->nr_zones - 1; i >= 0; i--) {
			struct zone *zone = pgdat->node_zones + i;
L
Linus Torvalds 已提交
1104

1105 1106
			if (!populated_zone(zone))
				continue;
L
Linus Torvalds 已提交
1107

1108 1109
			if (zone->all_unreclaimable && priority != DEF_PRIORITY)
				continue;
L
Linus Torvalds 已提交
1110

1111 1112 1113 1114
			if (!zone_watermark_ok(zone, order, zone->pages_high,
					       0, 0)) {
				end_zone = i;
				goto scan;
L
Linus Torvalds 已提交
1115 1116
			}
		}
1117
		goto out;
L
Linus Torvalds 已提交
1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135
scan:
		for (i = 0; i <= end_zone; i++) {
			struct zone *zone = pgdat->node_zones + i;

			lru_pages += zone->nr_active + zone->nr_inactive;
		}

		/*
		 * 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;
1136
			int nr_slab;
L
Linus Torvalds 已提交
1137

1138
			if (!populated_zone(zone))
L
Linus Torvalds 已提交
1139 1140 1141 1142 1143
				continue;

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

1144 1145 1146
			if (!zone_watermark_ok(zone, order, zone->pages_high,
					       end_zone, 0))
				all_zones_ok = 0;
L
Linus Torvalds 已提交
1147 1148 1149 1150
			zone->temp_priority = priority;
			if (zone->prev_priority > priority)
				zone->prev_priority = priority;
			sc.nr_scanned = 0;
1151
			nr_reclaimed += shrink_zone(priority, zone, &sc);
L
Linus Torvalds 已提交
1152
			reclaim_state->reclaimed_slab = 0;
1153 1154
			nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
						lru_pages);
1155
			nr_reclaimed += reclaim_state->reclaimed_slab;
L
Linus Torvalds 已提交
1156 1157 1158
			total_scanned += sc.nr_scanned;
			if (zone->all_unreclaimable)
				continue;
1159 1160
			if (nr_slab == 0 && zone->pages_scanned >=
				    (zone->nr_active + zone->nr_inactive) * 4)
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				zone->all_unreclaimable = 1;
			/*
			 * 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 &&
1168
			    total_scanned > nr_reclaimed + nr_reclaimed / 2)
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				sc.may_writepage = 1;
		}
		if (all_zones_ok)
			break;		/* kswapd: all done */
		/*
		 * OK, kswapd is getting into trouble.  Take a nap, then take
		 * another pass across the zones.
		 */
		if (total_scanned && priority < DEF_PRIORITY - 2)
			blk_congestion_wait(WRITE, HZ/10);

		/*
		 * 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.
		 */
1186
		if (nr_reclaimed >= SWAP_CLUSTER_MAX)
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			break;
	}
out:
	for (i = 0; i < pgdat->nr_zones; i++) {
		struct zone *zone = pgdat->node_zones + i;

		zone->prev_priority = zone->temp_priority;
	}
	if (!all_zones_ok) {
		cond_resched();
		goto loop_again;
	}

1200
	return nr_reclaimed;
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}

/*
 * The background pageout daemon, started as a kernel thread
 * from the init process. 
 *
 * 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)
{
	unsigned long order;
	pg_data_t *pgdat = (pg_data_t*)p;
	struct task_struct *tsk = current;
	DEFINE_WAIT(wait);
	struct reclaim_state reclaim_state = {
		.reclaimed_slab = 0,
	};
	cpumask_t cpumask;

	cpumask = node_to_cpumask(pgdat->node_id);
	if (!cpus_empty(cpumask))
		set_cpus_allowed(tsk, cpumask);
	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).
	 */
1244
	tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
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	order = 0;
	for ( ; ; ) {
		unsigned long new_order;
1249 1250

		try_to_freeze();
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		prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
		new_order = pgdat->kswapd_max_order;
		pgdat->kswapd_max_order = 0;
		if (order < new_order) {
			/*
			 * Don't sleep if someone wants a larger 'order'
			 * allocation
			 */
			order = new_order;
		} else {
			schedule();
			order = pgdat->kswapd_max_order;
		}
		finish_wait(&pgdat->kswapd_wait, &wait);

1267
		balance_pgdat(pgdat, order);
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	}
	return 0;
}

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

1279
	if (!populated_zone(zone))
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		return;

	pgdat = zone->zone_pgdat;
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	if (zone_watermark_ok(zone, order, zone->pages_low, 0, 0))
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		return;
	if (pgdat->kswapd_max_order < order)
		pgdat->kswapd_max_order = order;
1287
	if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
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		return;
1289
	if (!waitqueue_active(&pgdat->kswapd_wait))
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		return;
1291
	wake_up_interruptible(&pgdat->kswapd_wait);
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}

#ifdef CONFIG_PM
/*
1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345
 * Helper function for shrink_all_memory().  Tries to reclaim 'nr_pages' pages
 * from LRU lists system-wide, for given pass and priority, and returns the
 * number of reclaimed pages
 *
 * For pass > 3 we also try to shrink the LRU lists that contain a few pages
 */
static unsigned long shrink_all_zones(unsigned long nr_pages, int pass,
				      int prio, struct scan_control *sc)
{
	struct zone *zone;
	unsigned long nr_to_scan, ret = 0;

	for_each_zone(zone) {

		if (!populated_zone(zone))
			continue;

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

		/* For pass = 0 we don't shrink the active list */
		if (pass > 0) {
			zone->nr_scan_active += (zone->nr_active >> prio) + 1;
			if (zone->nr_scan_active >= nr_pages || pass > 3) {
				zone->nr_scan_active = 0;
				nr_to_scan = min(nr_pages, zone->nr_active);
				shrink_active_list(nr_to_scan, zone, sc);
			}
		}

		zone->nr_scan_inactive += (zone->nr_inactive >> prio) + 1;
		if (zone->nr_scan_inactive >= nr_pages || pass > 3) {
			zone->nr_scan_inactive = 0;
			nr_to_scan = min(nr_pages, zone->nr_inactive);
			ret += shrink_inactive_list(nr_to_scan, zone, sc);
			if (ret >= nr_pages)
				return ret;
		}
	}

	return ret;
}

/*
 * Try to free `nr_pages' of memory, system-wide, and return the number of
 * 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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 */
1347
unsigned long shrink_all_memory(unsigned long nr_pages)
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{
1349
	unsigned long lru_pages, nr_slab;
1350
	unsigned long ret = 0;
1351 1352 1353 1354 1355 1356 1357 1358 1359
	int pass;
	struct reclaim_state reclaim_state;
	struct zone *zone;
	struct scan_control sc = {
		.gfp_mask = GFP_KERNEL,
		.may_swap = 0,
		.swap_cluster_max = nr_pages,
		.may_writepage = 1,
		.swappiness = vm_swappiness,
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	};

	current->reclaim_state = &reclaim_state;
1363

1364 1365 1366 1367 1368 1369 1370 1371 1372 1373
	lru_pages = 0;
	for_each_zone(zone)
		lru_pages += zone->nr_active + zone->nr_inactive;

	nr_slab = read_page_state(nr_slab);
	/* If slab caches are huge, it's better to hit them first */
	while (nr_slab >= lru_pages) {
		reclaim_state.reclaimed_slab = 0;
		shrink_slab(nr_pages, sc.gfp_mask, lru_pages);
		if (!reclaim_state.reclaimed_slab)
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			break;
1375 1376 1377 1378 1379 1380

		ret += reclaim_state.reclaimed_slab;
		if (ret >= nr_pages)
			goto out;

		nr_slab -= reclaim_state.reclaimed_slab;
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	}
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	/*
	 * We try to shrink LRUs in 5 passes:
	 * 0 = Reclaim from inactive_list only
	 * 1 = Reclaim from active list but don't reclaim mapped
	 * 2 = 2nd pass of type 1
	 * 3 = Reclaim mapped (normal reclaim)
	 * 4 = 2nd pass of type 3
	 */
	for (pass = 0; pass < 5; pass++) {
		int prio;

		/* Needed for shrinking slab caches later on */
		if (!lru_pages)
			for_each_zone(zone) {
				lru_pages += zone->nr_active;
				lru_pages += zone->nr_inactive;
			}

		/* Force reclaiming mapped pages in the passes #3 and #4 */
		if (pass > 2) {
			sc.may_swap = 1;
			sc.swappiness = 100;
		}

		for (prio = DEF_PRIORITY; prio >= 0; prio--) {
			unsigned long nr_to_scan = nr_pages - ret;

			sc.nr_mapped = read_page_state(nr_mapped);
			sc.nr_scanned = 0;

			ret += shrink_all_zones(nr_to_scan, prio, pass, &sc);
			if (ret >= nr_pages)
				goto out;

			reclaim_state.reclaimed_slab = 0;
			shrink_slab(sc.nr_scanned, sc.gfp_mask, lru_pages);
			ret += reclaim_state.reclaimed_slab;
			if (ret >= nr_pages)
				goto out;

			if (sc.nr_scanned && prio < DEF_PRIORITY - 2)
				blk_congestion_wait(WRITE, HZ / 10);
		}

		lru_pages = 0;
1428
	}
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	/*
	 * If ret = 0, we could not shrink LRUs, but there may be something
	 * in slab caches
	 */
	if (!ret)
		do {
			reclaim_state.reclaimed_slab = 0;
			shrink_slab(nr_pages, sc.gfp_mask, lru_pages);
			ret += reclaim_state.reclaimed_slab;
		} while (ret < nr_pages && reclaim_state.reclaimed_slab > 0);

out:
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	current->reclaim_state = NULL;
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	return ret;
}
#endif

#ifdef CONFIG_HOTPLUG_CPU
/* 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. */
1453
static int cpu_callback(struct notifier_block *nfb,
1454
				  unsigned long action, void *hcpu)
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{
	pg_data_t *pgdat;
	cpumask_t mask;

	if (action == CPU_ONLINE) {
1460
		for_each_online_pgdat(pgdat) {
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			mask = node_to_cpumask(pgdat->node_id);
			if (any_online_cpu(mask) != NR_CPUS)
				/* One of our CPUs online: restore mask */
				set_cpus_allowed(pgdat->kswapd, mask);
		}
	}
	return NOTIFY_OK;
}
#endif /* CONFIG_HOTPLUG_CPU */

1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492
/*
 * 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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static int __init kswapd_init(void)
{
1495
	int nid;
1496

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	swap_setup();
1498 1499
	for_each_online_node(nid)
 		kswapd_run(nid);
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	hotcpu_notifier(cpu_callback, 0);
	return 0;
}

module_init(kswapd_init)
1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518

#ifdef CONFIG_NUMA
/*
 * Zone reclaim mode
 *
 * If non-zero call zone_reclaim when the number of free pages falls below
 * the watermarks.
 *
 * In the future we may add flags to the mode. However, the page allocator
 * should only have to check that zone_reclaim_mode != 0 before calling
 * zone_reclaim().
 */
int zone_reclaim_mode __read_mostly;

1519 1520 1521 1522
#define RECLAIM_OFF 0
#define RECLAIM_ZONE (1<<0)	/* Run shrink_cache on the zone */
#define RECLAIM_WRITE (1<<1)	/* Writeout pages during reclaim */
#define RECLAIM_SWAP (1<<2)	/* Swap pages out during reclaim */
1523
#define RECLAIM_SLAB (1<<3)	/* Do a global slab shrink if the zone is out of memory */
1524

1525 1526 1527
/*
 * Mininum time between zone reclaim scans
 */
1528
int zone_reclaim_interval __read_mostly = 30*HZ;
1529 1530 1531 1532 1533 1534 1535 1536

/*
 * 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

1537 1538 1539
/*
 * Try to free up some pages from this zone through reclaim.
 */
1540
static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
1541
{
1542
	/* Minimum pages needed in order to stay on node */
1543
	const unsigned long nr_pages = 1 << order;
1544 1545
	struct task_struct *p = current;
	struct reclaim_state reclaim_state;
1546
	int priority;
1547
	unsigned long nr_reclaimed = 0;
1548 1549 1550 1551
	struct scan_control sc = {
		.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
		.may_swap = !!(zone_reclaim_mode & RECLAIM_SWAP),
		.nr_mapped = read_page_state(nr_mapped),
1552 1553
		.swap_cluster_max = max_t(unsigned long, nr_pages,
					SWAP_CLUSTER_MAX),
1554
		.gfp_mask = gfp_mask,
1555
		.swappiness = vm_swappiness,
1556
	};
1557 1558 1559

	disable_swap_token();
	cond_resched();
1560 1561 1562 1563 1564 1565
	/*
	 * 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;
1566 1567
	reclaim_state.reclaimed_slab = 0;
	p->reclaim_state = &reclaim_state;
1568

1569 1570 1571 1572
	/*
	 * Free memory by calling shrink zone with increasing priorities
	 * until we have enough memory freed.
	 */
1573
	priority = ZONE_RECLAIM_PRIORITY;
1574
	do {
1575
		nr_reclaimed += shrink_zone(priority, zone, &sc);
1576
		priority--;
1577
	} while (priority >= 0 && nr_reclaimed < nr_pages);
1578

1579
	if (nr_reclaimed < nr_pages && (zone_reclaim_mode & RECLAIM_SLAB)) {
1580
		/*
1581 1582 1583 1584 1585 1586
		 * shrink_slab() does not currently allow us to determine how
		 * many pages were freed in this zone. So we just shake the slab
		 * a bit and then go off node for this particular allocation
		 * despite possibly having freed enough memory to allocate in
		 * this zone.  If we freed local memory then the next
		 * allocations will be local again.
1587 1588 1589 1590 1591 1592 1593
		 *
		 * shrink_slab will free memory on all zones and may take
		 * a long time.
		 */
		shrink_slab(sc.nr_scanned, gfp_mask, order);
	}

1594
	p->reclaim_state = NULL;
1595
	current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
1596

1597 1598 1599 1600 1601 1602
	if (nr_reclaimed == 0) {
		/*
		 * We were unable to reclaim enough pages to stay on node.  We
		 * now allow off node accesses for a certain time period before
		 * trying again to reclaim pages from the local zone.
		 */
1603
		zone->last_unsuccessful_zone_reclaim = jiffies;
1604
	}
1605

1606
	return nr_reclaimed >= nr_pages;
1607
}
1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622 1623 1624 1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646

int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
{
	cpumask_t mask;
	int node_id;

	/*
	 * Do not reclaim if there was a recent unsuccessful attempt at zone
	 * reclaim.  In that case we let allocations go off node for the
	 * zone_reclaim_interval.  Otherwise we would scan for each off-node
	 * page allocation.
	 */
	if (time_before(jiffies,
		zone->last_unsuccessful_zone_reclaim + zone_reclaim_interval))
			return 0;

	/*
	 * Avoid concurrent zone reclaims, do not reclaim in a zone that does
	 * not have reclaimable pages and if we should not delay the allocation
	 * then do not scan.
	 */
	if (!(gfp_mask & __GFP_WAIT) ||
		zone->all_unreclaimable ||
		atomic_read(&zone->reclaim_in_progress) > 0 ||
		(current->flags & PF_MEMALLOC))
			return 0;

	/*
	 * 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.
	 */
	node_id = zone->zone_pgdat->node_id;
	mask = node_to_cpumask(node_id);
	if (!cpus_empty(mask) && node_id != numa_node_id())
		return 0;
	return __zone_reclaim(zone, gfp_mask, order);
}
1647
#endif