/*
   *  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/gfp.h>

  #include <linux/kernel_stat.h>
  #include <linux/swap.h>
  #include <linux/pagemap.h>
  #include <linux/init.h>
  #include <linux/highmem.h>

  #include <linux/vmstat.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/compaction.h>

  #include <linux/notifier.h>
  #include <linux/rwsem.h>

  #include <linux/delay.h>

  #include <linux/kthread.h>

  #include <linux/freezer.h>

  #include <linux/memcontrol.h>

  #include <linux/delayacct.h>

  #include <linux/sysctl.h>

  #include <linux/oom.h>

  #include <linux/prefetch.h>

  
  #include <asm/tlbflush.h>
  #include <asm/div64.h>
  
  #include <linux/swapops.h>

  #include "internal.h"

  #define CREATE_TRACE_POINTS
  #include <trace/events/vmscan.h>

  /*

   * reclaim_mode determines how the inactive list is shrunk
   * RECLAIM_MODE_SINGLE: Reclaim only order-0 pages
   * RECLAIM_MODE_ASYNC:  Do not block
   * RECLAIM_MODE_SYNC:   Allow blocking e.g. call wait_on_page_writeback
   * RECLAIM_MODE_LUMPYRECLAIM: For high-order allocations, take a reference

   *			page from the LRU and reclaim all pages within a
   *			naturally aligned range

   * RECLAIM_MODE_COMPACTION: For high-order allocations, reclaim a number of

   *			order-0 pages and then compact the zone

   */

  typedef unsigned __bitwise__ reclaim_mode_t;
  #define RECLAIM_MODE_SINGLE		((__force reclaim_mode_t)0x01u)
  #define RECLAIM_MODE_ASYNC		((__force reclaim_mode_t)0x02u)
  #define RECLAIM_MODE_SYNC		((__force reclaim_mode_t)0x04u)
  #define RECLAIM_MODE_LUMPYRECLAIM	((__force reclaim_mode_t)0x08u)
  #define RECLAIM_MODE_COMPACTION		((__force reclaim_mode_t)0x10u)

  struct scan_control {

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

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

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

  	unsigned long hibernation_mode;

  	/* This context's GFP mask */

  	gfp_t gfp_mask;

  
  	int may_writepage;

  	/* Can mapped pages be reclaimed? */
  	int may_unmap;

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

  	int order;

  	/*

  	 * Intend to reclaim enough continuous memory rather than reclaim
  	 * enough amount of memory. i.e, mode for high order allocation.

  	 */

  	reclaim_mode_t reclaim_mode;

  	/* Which cgroup do we reclaim from */
  	struct mem_cgroup *mem_cgroup;

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

  };

  #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;

  long vm_total_pages;	/* The total number of pages which the VM controls */

  
  static LIST_HEAD(shrinker_list);
  static DECLARE_RWSEM(shrinker_rwsem);

  #ifdef CONFIG_CGROUP_MEM_RES_CTLR

  #define scanning_global_lru(sc)	(!(sc)->mem_cgroup)

  #else

  #define scanning_global_lru(sc)	(1)

  #endif

  static struct zone_reclaim_stat *get_reclaim_stat(struct zone *zone,
  						  struct scan_control *sc)
  {

  	if (!scanning_global_lru(sc))

  		return mem_cgroup_get_reclaim_stat(sc->mem_cgroup, zone);

  	return &zone->reclaim_stat;
  }

  static unsigned long zone_nr_lru_pages(struct zone *zone,
  				struct scan_control *sc, enum lru_list lru)

  {

  	if (!scanning_global_lru(sc))

  		return mem_cgroup_zone_nr_lru_pages(sc->mem_cgroup,
  				zone_to_nid(zone), zone_idx(zone), BIT(lru));

  	return zone_page_state(zone, NR_LRU_BASE + lru);
  }

  /*
   * Add a shrinker callback to be called from the vm
   */

  void register_shrinker(struct shrinker *shrinker)

  {

  	atomic_long_set(&shrinker->nr_in_batch, 0);

  	down_write(&shrinker_rwsem);
  	list_add_tail(&shrinker->list, &shrinker_list);
  	up_write(&shrinker_rwsem);

  }

  EXPORT_SYMBOL(register_shrinker);

  
  /*
   * Remove one
   */

  void unregister_shrinker(struct shrinker *shrinker)

  {
  	down_write(&shrinker_rwsem);
  	list_del(&shrinker->list);
  	up_write(&shrinker_rwsem);

  }

  EXPORT_SYMBOL(unregister_shrinker);

  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);
  }

  #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 encountered 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.

   *
   * Returns the number of slab objects which we shrunk.

   */

  unsigned long shrink_slab(struct shrink_control *shrink,

  			  unsigned long nr_pages_scanned,

  			  unsigned long lru_pages)

  {
  	struct shrinker *shrinker;

  	unsigned long ret = 0;

  	if (nr_pages_scanned == 0)
  		nr_pages_scanned = SWAP_CLUSTER_MAX;

  	if (!down_read_trylock(&shrinker_rwsem)) {
  		/* Assume we'll be able to shrink next time */
  		ret = 1;
  		goto out;
  	}

  
  	list_for_each_entry(shrinker, &shrinker_list, list) {
  		unsigned long long delta;

  		long total_scan;
  		long max_pass;

  		int shrink_ret = 0;

  		long nr;
  		long new_nr;

  		long batch_size = shrinker->batch ? shrinker->batch
  						  : SHRINK_BATCH;

  		max_pass = do_shrinker_shrink(shrinker, shrink, 0);
  		if (max_pass <= 0)
  			continue;

  		/*
  		 * copy the current shrinker scan count into a local variable
  		 * and zero it so that other concurrent shrinker invocations
  		 * don't also do this scanning work.
  		 */

  		nr = atomic_long_xchg(&shrinker->nr_in_batch, 0);

  
  		total_scan = nr;

  		delta = (4 * nr_pages_scanned) / shrinker->seeks;

  		delta *= max_pass;

  		do_div(delta, lru_pages + 1);

  		total_scan += delta;
  		if (total_scan < 0) {

  			printk(KERN_ERR "shrink_slab: %pF negative objects to "
  			       "delete nr=%ld
  ",

  			       shrinker->shrink, total_scan);
  			total_scan = max_pass;

  		}
  
  		/*

  		 * 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);
  
  		/*

  		 * Avoid risking looping forever due to too large nr value:
  		 * never try to free more than twice the estimate number of
  		 * freeable entries.
  		 */

  		if (total_scan > max_pass * 2)
  			total_scan = max_pass * 2;

  		trace_mm_shrink_slab_start(shrinker, shrink, nr,

  					nr_pages_scanned, lru_pages,
  					max_pass, delta, total_scan);

  		while (total_scan >= batch_size) {

  			int nr_before;

  			nr_before = do_shrinker_shrink(shrinker, shrink, 0);
  			shrink_ret = do_shrinker_shrink(shrinker, shrink,

  							batch_size);

  			if (shrink_ret == -1)
  				break;

  			if (shrink_ret < nr_before)
  				ret += nr_before - shrink_ret;

  			count_vm_events(SLABS_SCANNED, batch_size);
  			total_scan -= batch_size;

  
  			cond_resched();
  		}

  		/*
  		 * move the unused scan count back into the shrinker in a
  		 * manner that handles concurrent updates. If we exhausted the
  		 * scan, there is no need to do an update.
  		 */

  		if (total_scan > 0)
  			new_nr = atomic_long_add_return(total_scan,
  					&shrinker->nr_in_batch);
  		else
  			new_nr = atomic_long_read(&shrinker->nr_in_batch);

  
  		trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr);

  	}
  	up_read(&shrinker_rwsem);

  out:
  	cond_resched();

  	return ret;

  }

  static void set_reclaim_mode(int priority, struct scan_control *sc,

  				   bool sync)
  {

  	reclaim_mode_t syncmode = sync ? RECLAIM_MODE_SYNC : RECLAIM_MODE_ASYNC;

  
  	/*

  	 * Initially assume we are entering either lumpy reclaim or
  	 * reclaim/compaction.Depending on the order, we will either set the
  	 * sync mode or just reclaim order-0 pages later.

  	 */

  	if (COMPACTION_BUILD)

  		sc->reclaim_mode = RECLAIM_MODE_COMPACTION;

  	else

  		sc->reclaim_mode = RECLAIM_MODE_LUMPYRECLAIM;

  
  	/*

  	 * Avoid using lumpy reclaim or reclaim/compaction if possible by
  	 * restricting when its set to either costly allocations or when
  	 * under memory pressure

  	 */
  	if (sc->order > PAGE_ALLOC_COSTLY_ORDER)

  		sc->reclaim_mode |= syncmode;

  	else if (sc->order && priority < DEF_PRIORITY - 2)

  		sc->reclaim_mode |= syncmode;

  	else

  		sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC;

  }

  static void reset_reclaim_mode(struct scan_control *sc)

  {

  	sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC;

  }

  static inline int is_page_cache_freeable(struct page *page)
  {

  	/*
  	 * 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.
  	 */

  	return page_count(page) - page_has_private(page) == 2;

  }

  static int may_write_to_queue(struct backing_dev_info *bdi,
  			      struct scan_control *sc)

  {

  	if (current->flags & PF_SWAPWRITE)

  		return 1;
  	if (!bdi_write_congested(bdi))
  		return 1;
  	if (bdi == current->backing_dev_info)
  		return 1;

  
  	/* lumpy reclaim for hugepage often need a lot of write */
  	if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
  		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)
  		mapping_set_error(mapping, error);

  	unlock_page(page);
  }

  /* 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;

  /*

   * pageout is called by shrink_page_list() for each dirty page.
   * Calls ->writepage().

   */

  static pageout_t pageout(struct page *page, struct address_space *mapping,

  			 struct scan_control *sc)

  {
  	/*
  	 * 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_aio_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.

  	 */
  	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.
  		 */

  		if (page_has_private(page)) {

  			if (try_to_free_buffers(page)) {
  				ClearPageDirty(page);

  				printk("%s: orphaned page
  ", __func__);

  				return PAGE_CLEAN;
  			}
  		}
  		return PAGE_KEEP;
  	}
  	if (mapping->a_ops->writepage == NULL)
  		return PAGE_ACTIVATE;

  	if (!may_write_to_queue(mapping->backing_dev_info, sc))

  		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,

  			.range_start = 0,
  			.range_end = LLONG_MAX,

  			.for_reclaim = 1,
  		};
  
  		SetPageReclaim(page);
  		res = mapping->a_ops->writepage(page, &wbc);
  		if (res < 0)
  			handle_write_error(mapping, page, res);

  		if (res == AOP_WRITEPAGE_ACTIVATE) {

  			ClearPageReclaim(page);
  			return PAGE_ACTIVATE;
  		}

  		if (!PageWriteback(page)) {
  			/* synchronous write or broken a_ops? */
  			ClearPageReclaim(page);
  		}

  		trace_mm_vmscan_writepage(page,

  			trace_reclaim_flags(page, sc->reclaim_mode));

  		inc_zone_page_state(page, NR_VMSCAN_WRITE);

  		return PAGE_SUCCESS;
  	}
  
  	return PAGE_CLEAN;
  }

  /*

   * Same as remove_mapping, but if the page is removed from the mapping, it
   * gets returned with a refcount of 0.

   */

  static int __remove_mapping(struct address_space *mapping, struct page *page)

  {

  	BUG_ON(!PageLocked(page));
  	BUG_ON(mapping != page_mapping(page));

  	spin_lock_irq(&mapping->tree_lock);

  	/*

  	 * 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.

  	 */

  	if (!page_freeze_refs(page, 2))

  		goto cannot_free;

  	/* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
  	if (unlikely(PageDirty(page))) {
  		page_unfreeze_refs(page, 2);

  		goto cannot_free;

  	}

  
  	if (PageSwapCache(page)) {
  		swp_entry_t swap = { .val = page_private(page) };
  		__delete_from_swap_cache(page);

  		spin_unlock_irq(&mapping->tree_lock);

  		swapcache_free(swap, page);

  	} else {

  		void (*freepage)(struct page *);
  
  		freepage = mapping->a_ops->freepage;

  		__delete_from_page_cache(page);

  		spin_unlock_irq(&mapping->tree_lock);

  		mem_cgroup_uncharge_cache_page(page);

  
  		if (freepage != NULL)
  			freepage(page);

  	}

  	return 1;
  
  cannot_free:

  	spin_unlock_irq(&mapping->tree_lock);

  	return 0;
  }

  /*

   * 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;
  }

  /**
   * 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);

  	int was_unevictable = PageUnevictable(page);

  
  	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.
  		 */

  		lru = active + page_lru_base_type(page);

  		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);

  		/*

  		 * 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
  		 * isolation/check_move_unevictable_page,
  		 * we see PG_mlocked/AS_UNEVICTABLE cleared below and move

  		 * the page back to the evictable list.
  		 *

  		 * The other side is TestClearPageMlocked() or shmem_lock().

  		 */
  		smp_mb();

  	}

  
  	/*
  	 * 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.
  		 */
  	}

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

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

  enum page_references {
  	PAGEREF_RECLAIM,
  	PAGEREF_RECLAIM_CLEAN,

  	PAGEREF_KEEP,

  	PAGEREF_ACTIVATE,
  };
  
  static enum page_references page_check_references(struct page *page,
  						  struct scan_control *sc)
  {

  	int referenced_ptes, referenced_page;

  	unsigned long vm_flags;

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

  
  	/* Lumpy reclaim - ignore references */

  	if (sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM)

  		return PAGEREF_RECLAIM;
  
  	/*
  	 * 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;

  	if (referenced_ptes) {
  		if (PageAnon(page))
  			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);
  
  		if (referenced_page)
  			return PAGEREF_ACTIVATE;
  
  		return PAGEREF_KEEP;
  	}

  
  	/* Reclaim if clean, defer dirty pages to writeback */

  	if (referenced_page && !PageSwapBacked(page))

  		return PAGEREF_RECLAIM_CLEAN;
  
  	return PAGEREF_RECLAIM;

  }

  static noinline_for_stack void free_page_list(struct list_head *free_pages)
  {
  	struct pagevec freed_pvec;
  	struct page *page, *tmp;
  
  	pagevec_init(&freed_pvec, 1);
  
  	list_for_each_entry_safe(page, tmp, free_pages, lru) {
  		list_del(&page->lru);
  		if (!pagevec_add(&freed_pvec, page)) {
  			__pagevec_free(&freed_pvec);
  			pagevec_reinit(&freed_pvec);
  		}
  	}
  
  	pagevec_free(&freed_pvec);
  }

  /*

   * shrink_page_list() returns the number of reclaimed pages

   */

  static unsigned long shrink_page_list(struct list_head *page_list,

  				      struct zone *zone,

  				      struct scan_control *sc,

  				      int priority,
  				      unsigned long *ret_nr_dirty,
  				      unsigned long *ret_nr_writeback)

  {
  	LIST_HEAD(ret_pages);

  	LIST_HEAD(free_pages);

  	int pgactivate = 0;

  	unsigned long nr_dirty = 0;
  	unsigned long nr_congested = 0;

  	unsigned long nr_reclaimed = 0;

  	unsigned long nr_writeback = 0;

  
  	cond_resched();

  	while (!list_empty(page_list)) {

  		enum page_references references;

  		struct address_space *mapping;
  		struct page *page;
  		int may_enter_fs;

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

  		if (!trylock_page(page))

  			goto keep;

  		VM_BUG_ON(PageActive(page));

  		VM_BUG_ON(page_zone(page) != zone);

  
  		sc->nr_scanned++;

  		if (unlikely(!page_evictable(page, NULL)))
  			goto cull_mlocked;

  		if (!sc->may_unmap && page_mapped(page))

  			goto keep_locked;

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

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

  			nr_writeback++;

  			/*

  			 * Synchronous reclaim cannot queue pages for
  			 * writeback due to the possibility of stack overflow
  			 * but if it encounters a page under writeback, wait
  			 * for the IO to complete.

  			 */

  			if ((sc->reclaim_mode & RECLAIM_MODE_SYNC) &&

  			    may_enter_fs)

  				wait_on_page_writeback(page);

  			else {
  				unlock_page(page);
  				goto keep_lumpy;
  			}

  		}

  		references = page_check_references(page, sc);
  		switch (references) {
  		case PAGEREF_ACTIVATE:

  			goto activate_locked;

  		case PAGEREF_KEEP:
  			goto keep_locked;

  		case PAGEREF_RECLAIM:
  		case PAGEREF_RECLAIM_CLEAN:
  			; /* try to reclaim the page below */
  		}

  		/*
  		 * Anonymous process memory has backing store?
  		 * Try to allocate it some swap space here.
  		 */

  		if (PageAnon(page) && !PageSwapCache(page)) {

  			if (!(sc->gfp_mask & __GFP_IO))
  				goto keep_locked;

  			if (!add_to_swap(page))

  				goto activate_locked;

  			may_enter_fs = 1;

  		}

  
  		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) {

  			switch (try_to_unmap(page, TTU_UNMAP)) {

  			case SWAP_FAIL:
  				goto activate_locked;
  			case SWAP_AGAIN:
  				goto keep_locked;

  			case SWAP_MLOCK:
  				goto cull_mlocked;

  			case SWAP_SUCCESS:
  				; /* try to free the page below */
  			}
  		}
  
  		if (PageDirty(page)) {

  			nr_dirty++;

  			/*
  			 * Only kswapd can writeback filesystem pages to

  			 * avoid risk of stack overflow but do not writeback
  			 * unless under significant pressure.

  			 */

  			if (page_is_file_cache(page) &&
  					(!current_is_kswapd() || priority >= DEF_PRIORITY - 2)) {

  				/*
  				 * 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);

  				goto keep_locked;
  			}

  			if (references == PAGEREF_RECLAIM_CLEAN)

  				goto keep_locked;

  			if (!may_enter_fs)

  				goto keep_locked;

  			if (!sc->may_writepage)

  				goto keep_locked;
  
  			/* Page is dirty, try to write it out here */

  			switch (pageout(page, mapping, sc)) {

  			case PAGE_KEEP:

  				nr_congested++;

  				goto keep_locked;
  			case PAGE_ACTIVATE:
  				goto activate_locked;
  			case PAGE_SUCCESS:

  				if (PageWriteback(page))
  					goto keep_lumpy;
  				if (PageDirty(page))

  					goto keep;

  				/*
  				 * A synchronous write - probably a ramdisk.  Go
  				 * ahead and try to reclaim the page.
  				 */

  				if (!trylock_page(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 (page_has_private(page)) {

  			if (!try_to_release_page(page, sc->gfp_mask))
  				goto activate_locked;

  			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;
  				}
  			}

  		}

  		if (!mapping || !__remove_mapping(mapping, page))

  			goto keep_locked;

  		/*
  		 * 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);

  free_it:

  		nr_reclaimed++;

  
  		/*
  		 * Is there need to periodically free_page_list? It would
  		 * appear not as the counts should be low
  		 */
  		list_add(&page->lru, &free_pages);

  		continue;

  cull_mlocked:

  		if (PageSwapCache(page))
  			try_to_free_swap(page);

  		unlock_page(page);
  		putback_lru_page(page);

  		reset_reclaim_mode(sc);

  		continue;

  activate_locked:

  		/* Not a candidate for swapping, so reclaim swap space. */
  		if (PageSwapCache(page) && vm_swap_full())

  			try_to_free_swap(page);

  		VM_BUG_ON(PageActive(page));

  		SetPageActive(page);
  		pgactivate++;
  keep_locked:
  		unlock_page(page);
  keep:

  		reset_reclaim_mode(sc);

  keep_lumpy:

  		list_add(&page->lru, &ret_pages);

  		VM_BUG_ON(PageLRU(page) || PageUnevictable(page));

  	}

  	/*
  	 * 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
  	 */

  	if (nr_dirty && nr_dirty == nr_congested && scanning_global_lru(sc))

  		zone_set_flag(zone, ZONE_CONGESTED);

  	free_page_list(&free_pages);

  	list_splice(&ret_pages, page_list);

  	count_vm_events(PGACTIVATE, pgactivate);

  	*ret_nr_dirty += nr_dirty;
  	*ret_nr_writeback += nr_writeback;

  	return nr_reclaimed;

  }

  /*
   * 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.
   */

  int __isolate_lru_page(struct page *page, isolate_mode_t mode, int file)

  {

  	bool all_lru_mode;

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

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

  	/*
  	 * When checking the active state, we need to be sure we are
  	 * dealing with comparible boolean values.  Take the logical not
  	 * of each.
  	 */

  	if (!all_lru_mode && !PageActive(page) != !(mode & ISOLATE_ACTIVE))

  		return ret;

  	if (!all_lru_mode && !!page_is_file_cache(page) != file)

  		return ret;

  	/*
  	 * When this function is being called for lumpy reclaim, we
  	 * initially look into all LRU pages, active, inactive and
  	 * unevictable; only give shrink_page_list evictable pages.
  	 */
  	if (PageUnevictable(page))
  		return ret;

  	ret = -EBUSY;

  	if ((mode & ISOLATE_CLEAN) && (PageDirty(page) || PageWriteback(page)))
  		return ret;

  	if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
  		return ret;

  	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;
  }

  /*

   * 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.

   * @order:	The caller's attempted allocation order
   * @mode:	One of the LRU isolation modes

   * @file:	True [1] if isolating file [!anon] pages

   *
   * returns how many pages were moved onto *@dst.
   */

  static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
  		struct list_head *src, struct list_head *dst,

  		unsigned long *scanned, int order, isolate_mode_t mode,
  		int file)

  {

  	unsigned long nr_taken = 0;

  	unsigned long nr_lumpy_taken = 0;
  	unsigned long nr_lumpy_dirty = 0;
  	unsigned long nr_lumpy_failed = 0;

  	unsigned long scan;

  	for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {

  		struct page *page;
  		unsigned long pfn;
  		unsigned long end_pfn;
  		unsigned long page_pfn;
  		int zone_id;

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

  		VM_BUG_ON(!PageLRU(page));

  		switch (__isolate_lru_page(page, mode, file)) {

  		case 0:
  			list_move(&page->lru, dst);

  			mem_cgroup_del_lru(page);

  			nr_taken += hpage_nr_pages(page);

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

  			mem_cgroup_rotate_lru_list(page, page_lru(page));

  			continue;

  		default:
  			BUG();
  		}
  
  		if (!order)
  			continue;
  
  		/*
  		 * Attempt to take all pages in the order aligned region
  		 * surrounding the tag page.  Only take those pages of
  		 * the same active state as that tag page.  We may safely
  		 * round the target page pfn down to the requested order

  		 * as the mem_map is guaranteed valid out to MAX_ORDER,

  		 * where that page is in a different zone we will detect
  		 * it from its zone id and abort this block scan.
  		 */
  		zone_id = page_zone_id(page);
  		page_pfn = page_to_pfn(page);
  		pfn = page_pfn & ~((1 << order) - 1);
  		end_pfn = pfn + (1 << order);
  		for (; pfn < end_pfn; pfn++) {
  			struct page *cursor_page;
  
  			/* The target page is in the block, ignore it. */
  			if (unlikely(pfn == page_pfn))
  				continue;
  
  			/* Avoid holes within the zone. */
  			if (unlikely(!pfn_valid_within(pfn)))
  				break;
  
  			cursor_page = pfn_to_page(pfn);

  			/* Check that we have not crossed a zone boundary. */
  			if (unlikely(page_zone_id(cursor_page) != zone_id))

  				break;

  
  			/*
  			 * If we don't have enough swap space, reclaiming of
  			 * anon page which don't already have a swap slot is
  			 * pointless.
  			 */
  			if (nr_swap_pages <= 0 && PageAnon(cursor_page) &&

  			    !PageSwapCache(cursor_page))
  				break;

  			if (__isolate_lru_page(cursor_page, mode, file) == 0) {

  				list_move(&cursor_page->lru, dst);

  				mem_cgroup_del_lru(cursor_page);

  				nr_taken += hpage_nr_pages(page);

  				nr_lumpy_taken++;
  				if (PageDirty(cursor_page))
  					nr_lumpy_dirty++;

  				scan++;

  			} else {

  				/*
  				 * Check if the page is freed already.
  				 *
  				 * We can't use page_count() as that
  				 * requires compound_head and we don't
  				 * have a pin on the page here. If a
  				 * page is tail, we may or may not
  				 * have isolated the head, so assume
  				 * it's not free, it'd be tricky to
  				 * track the head status without a
  				 * page pin.
  				 */
  				if (!PageTail(cursor_page) &&
  				    !atomic_read(&cursor_page->_count))

  					continue;
  				break;

  			}
  		}

  
  		/* If we break out of the loop above, lumpy reclaim failed */
  		if (pfn < end_pfn)
  			nr_lumpy_failed++;

  	}
  
  	*scanned = scan;

  
  	trace_mm_vmscan_lru_isolate(order,
  			nr_to_scan, scan,
  			nr_taken,
  			nr_lumpy_taken, nr_lumpy_dirty, nr_lumpy_failed,
  			mode);

  	return nr_taken;
  }

  static unsigned long isolate_pages_global(unsigned long nr,
  					struct list_head *dst,
  					unsigned long *scanned, int order,

  					isolate_mode_t mode,
  					struct zone *z,	int active, int file)

  {

  	int lru = LRU_BASE;

  	if (active)

  		lru += LRU_ACTIVE;
  	if (file)
  		lru += LRU_FILE;
  	return isolate_lru_pages(nr, &z->lru[lru].list, dst, scanned, order,

  								mode, file);

  }

  /*

   * clear_active_flags() is a helper for shrink_active_list(), clearing
   * any active bits from the pages in the list.
   */

  static unsigned long clear_active_flags(struct list_head *page_list,
  					unsigned int *count)

  {
  	int nr_active = 0;

  	int lru;

  	struct page *page;

  	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;

  		}

  		if (count)

  			count[lru] += numpages;

  	}

  
  	return nr_active;
  }

  /**
   * 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

   * 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.

   *
   * 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;

  	VM_BUG_ON(!page_count(page));

  	if (PageLRU(page)) {
  		struct zone *zone = page_zone(page);
  
  		spin_lock_irq(&zone->lru_lock);

  		if (PageLRU(page)) {

  			int lru = page_lru(page);

  			ret = 0;

  			get_page(page);

  			ClearPageLRU(page);

  			del_page_from_lru_list(zone, page, lru);

  		}
  		spin_unlock_irq(&zone->lru_lock);
  	}
  	return ret;
  }

  /*

   * 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;
  
  	if (!scanning_global_lru(sc))
  		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;
  }
  
  /*

   * TODO: Try merging with migrations version of putback_lru_pages
   */
  static noinline_for_stack void

  putback_lru_pages(struct zone *zone, struct scan_control *sc,

  				unsigned long nr_anon, unsigned long nr_file,
  				struct list_head *page_list)
  {
  	struct page *page;
  	struct pagevec pvec;

  	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);

  
  	pagevec_init(&pvec, 1);
  
  	/*
  	 * Put back any unfreeable pages.
  	 */
  	spin_lock(&zone->lru_lock);
  	while (!list_empty(page_list)) {
  		int lru;
  		page = lru_to_page(page_list);
  		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;
  		}

  		SetPageLRU(page);

  		lru = page_lru(page);

  		add_page_to_lru_list(zone, page, lru);

  		if (is_active_lru(lru)) {
  			int file = is_file_lru(lru);

  			int numpages = hpage_nr_pages(page);
  			reclaim_stat->recent_rotated[file] += numpages;

  		}
  		if (!pagevec_add(&pvec, page)) {
  			spin_unlock_irq(&zone->lru_lock);
  			__pagevec_release(&pvec);
  			spin_lock_irq(&zone->lru_lock);
  		}
  	}
  	__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);
  	pagevec_release(&pvec);
  }

  static noinline_for_stack void update_isolated_counts(struct zone *zone,
  					struct scan_control *sc,
  					unsigned long *nr_anon,
  					unsigned long *nr_file,
  					struct list_head *isolated_list)
  {
  	unsigned long nr_active;
  	unsigned int count[NR_LRU_LISTS] = { 0, };
  	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
  
  	nr_active = clear_active_flags(isolated_list, count);
  	__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];
  	__mod_zone_page_state(zone, NR_ISOLATED_ANON, *nr_anon);
  	__mod_zone_page_state(zone, NR_ISOLATED_FILE, *nr_file);
  
  	reclaim_stat->recent_scanned[0] += *nr_anon;
  	reclaim_stat->recent_scanned[1] += *nr_file;
  }

  /*

   * Returns true if a direct reclaim should wait on pages under writeback.

   *
   * If we are direct reclaiming for contiguous pages and we do not reclaim
   * everything in the list, try again and wait for writeback IO to complete.
   * This will stall high-order allocations noticeably. Only do that when really
   * need to free the pages under high memory pressure.
   */
  static inline bool should_reclaim_stall(unsigned long nr_taken,
  					unsigned long nr_freed,
  					int priority,
  					struct scan_control *sc)
  {
  	int lumpy_stall_priority;
  
  	/* kswapd should not stall on sync IO */
  	if (current_is_kswapd())
  		return false;
  
  	/* Only stall on lumpy reclaim */

  	if (sc->reclaim_mode & RECLAIM_MODE_SINGLE)

  		return false;

  	/* If we have reclaimed everything on the isolated list, no stall */

  	if (nr_freed == nr_taken)
  		return false;
  
  	/*
  	 * For high-order allocations, there are two stall thresholds.
  	 * High-cost allocations stall immediately where as lower
  	 * order allocations such as stacks require the scanning
  	 * priority to be much higher before stalling.
  	 */
  	if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
  		lumpy_stall_priority = DEF_PRIORITY;
  	else
  		lumpy_stall_priority = DEF_PRIORITY / 3;
  
  	return priority <= lumpy_stall_priority;
  }
  
  /*

   * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
   * of reclaimed pages

   */

  static noinline_for_stack unsigned long
  shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,
  			struct scan_control *sc, int priority, int file)

  {
  	LIST_HEAD(page_list);

  	unsigned long nr_scanned;

  	unsigned long nr_reclaimed = 0;

  	unsigned long nr_taken;

  	unsigned long nr_anon;
  	unsigned long nr_file;

  	unsigned long nr_dirty = 0;
  	unsigned long nr_writeback = 0;

  	isolate_mode_t reclaim_mode = ISOLATE_INACTIVE;

  	while (unlikely(too_many_isolated(zone, file, sc))) {

  		congestion_wait(BLK_RW_ASYNC, HZ/10);

  
  		/* We are about to die and free our memory. Return now. */
  		if (fatal_signal_pending(current))
  			return SWAP_CLUSTER_MAX;
  	}

  	set_reclaim_mode(priority, sc, false);

  	if (sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM)
  		reclaim_mode |= ISOLATE_ACTIVE;

  	lru_add_drain();

  
  	if (!sc->may_unmap)
  		reclaim_mode |= ISOLATE_UNMAPPED;
  	if (!sc->may_writepage)
  		reclaim_mode |= ISOLATE_CLEAN;

  	spin_lock_irq(&zone->lru_lock);

  	if (scanning_global_lru(sc)) {

  		nr_taken = isolate_pages_global(nr_to_scan, &page_list,
  			&nr_scanned, sc->order, reclaim_mode, zone, 0, file);

  		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);
  	} else {

  		nr_taken = mem_cgroup_isolate_pages(nr_to_scan, &page_list,
  			&nr_scanned, sc->order, reclaim_mode, zone,
  			sc->mem_cgroup, 0, file);

  		/*
  		 * mem_cgroup_isolate_pages() keeps track of
  		 * scanned pages on its own.
  		 */
  	}

  	if (nr_taken == 0) {
  		spin_unlock_irq(&zone->lru_lock);
  		return 0;
  	}

  	update_isolated_counts(zone, sc, &nr_anon, &nr_file, &page_list);

  	spin_unlock_irq(&zone->lru_lock);

  	nr_reclaimed = shrink_page_list(&page_list, zone, sc, priority,
  						&nr_dirty, &nr_writeback);

  	/* Check if we should syncronously wait for writeback */
  	if (should_reclaim_stall(nr_taken, nr_reclaimed, priority, sc)) {

  		set_reclaim_mode(priority, sc, true);

  		nr_reclaimed += shrink_page_list(&page_list, zone, sc,
  					priority, &nr_dirty, &nr_writeback);

  	}

  	local_irq_disable();
  	if (current_is_kswapd())
  		__count_vm_events(KSWAPD_STEAL, nr_reclaimed);
  	__count_zone_vm_events(PGSTEAL, zone, nr_reclaimed);

  	putback_lru_pages(zone, sc, nr_anon, nr_file, &page_list);

  	/*
  	 * 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);

  	trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
  		zone_idx(zone),
  		nr_scanned, nr_reclaimed,
  		priority,

  		trace_shrink_flags(file, sc->reclaim_mode));

  	return nr_reclaimed;

  }

  /*

   * 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.
   */

  static void move_active_pages_to_lru(struct zone *zone,
  				     struct list_head *list,
  				     enum lru_list lru)
  {
  	unsigned long pgmoved = 0;
  	struct pagevec pvec;
  	struct page *page;
  
  	pagevec_init(&pvec, 1);
  
  	while (!list_empty(list)) {
  		page = lru_to_page(list);

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

  		list_move(&page->lru, &zone->lru[lru].list);
  		mem_cgroup_add_lru_list(page, lru);

  		pgmoved += hpage_nr_pages(page);

  
  		if (!pagevec_add(&pvec, page) || list_empty(list)) {
  			spin_unlock_irq(&zone->lru_lock);
  			if (buffer_heads_over_limit)
  				pagevec_strip(&pvec);
  			__pagevec_release(&pvec);
  			spin_lock_irq(&zone->lru_lock);
  		}
  	}
  	__mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
  	if (!is_active_lru(lru))
  		__count_vm_events(PGDEACTIVATE, pgmoved);
  }

  static void shrink_active_list(unsigned long nr_pages, struct zone *zone,

  			struct scan_control *sc, int priority, int file)

  {

  	unsigned long nr_taken;

  	unsigned long pgscanned;

  	unsigned long vm_flags;

  	LIST_HEAD(l_hold);	/* The pages which were snipped off */

  	LIST_HEAD(l_active);

  	LIST_HEAD(l_inactive);

  	struct page *page;

  	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);

  	unsigned long nr_rotated = 0;

  	isolate_mode_t reclaim_mode = ISOLATE_ACTIVE;

  
  	lru_add_drain();

  
  	if (!sc->may_unmap)
  		reclaim_mode |= ISOLATE_UNMAPPED;
  	if (!sc->may_writepage)
  		reclaim_mode |= ISOLATE_CLEAN;

  	spin_lock_irq(&zone->lru_lock);

  	if (scanning_global_lru(sc)) {

  		nr_taken = isolate_pages_global(nr_pages, &l_hold,
  						&pgscanned, sc->order,

  						reclaim_mode, zone,

  						1, file);

  		zone->pages_scanned += pgscanned;

  	} else {
  		nr_taken = mem_cgroup_isolate_pages(nr_pages, &l_hold,
  						&pgscanned, sc->order,

  						reclaim_mode, zone,

  						sc->mem_cgroup, 1, file);
  		/*
  		 * mem_cgroup_isolate_pages() keeps track of
  		 * scanned pages on its own.
  		 */

  	}

  	reclaim_stat->recent_scanned[file] += nr_taken;

  	__count_zone_vm_events(PGREFILL, zone, pgscanned);

  	if (file)

  		__mod_zone_page_state(zone, NR_ACTIVE_FILE, -nr_taken);

  	else

  		__mod_zone_page_state(zone, NR_ACTIVE_ANON, -nr_taken);

  	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);

  	spin_unlock_irq(&zone->lru_lock);

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

  		if (unlikely(!page_evictable(page, NULL))) {
  			putback_lru_page(page);
  			continue;
  		}

  		if (page_referenced(page, 0, sc->mem_cgroup, &vm_flags)) {

  			nr_rotated += hpage_nr_pages(page);

  			/*
  			 * 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.
  			 */

  			if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {

  				list_add(&page->lru, &l_active);
  				continue;
  			}
  		}

  		ClearPageActive(page);	/* we are de-activating */

  		list_add(&page->lru, &l_inactive);
  	}

  	/*

  	 * Move pages back to the lru list.

  	 */

  	spin_lock_irq(&zone->lru_lock);

  	/*

  	 * 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.

  	 */

  	reclaim_stat->recent_rotated[file] += nr_rotated;

  	move_active_pages_to_lru(zone, &l_active,
  						LRU_ACTIVE + file * LRU_FILE);
  	move_active_pages_to_lru(zone, &l_inactive,
  						LRU_BASE   + file * LRU_FILE);

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

  	spin_unlock_irq(&zone->lru_lock);

  }

  #ifdef CONFIG_SWAP

  static int inactive_anon_is_low_global(struct zone *zone)

  {
  	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;
  }

  /**
   * 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.
   */
  static int inactive_anon_is_low(struct zone *zone, struct scan_control *sc)
  {
  	int low;

  	/*
  	 * If we don't have swap space, anonymous page deactivation
  	 * is pointless.
  	 */
  	if (!total_swap_pages)
  		return 0;

  	if (scanning_global_lru(sc))

  		low = inactive_anon_is_low_global(zone);
  	else

  		low = mem_cgroup_inactive_anon_is_low(sc->mem_cgroup, zone);

  	return low;
  }

  #else
  static inline int inactive_anon_is_low(struct zone *zone,
  					struct scan_control *sc)
  {
  	return 0;
  }
  #endif

  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
   * @zone: zone to check
   * @sc:   scan control of this context
   *
   * 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.
   */
  static int inactive_file_is_low(struct zone *zone, struct scan_control *sc)
  {
  	int low;
  
  	if (scanning_global_lru(sc))
  		low = inactive_file_is_low_global(zone);
  	else

  		low = mem_cgroup_inactive_file_is_low(sc->mem_cgroup, zone);

  	return low;
  }

  static int inactive_list_is_low(struct zone *zone, struct scan_control *sc,
  				int file)
  {
  	if (file)
  		return inactive_file_is_low(zone, sc);
  	else
  		return inactive_anon_is_low(zone, sc);
  }

  static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,

  	struct zone *zone, struct scan_control *sc, int priority)
  {

  	int file = is_file_lru(lru);

  	if (is_active_lru(lru)) {
  		if (inactive_list_is_low(zone, sc, file))
  		    shrink_active_list(nr_to_scan, zone, sc, priority, file);

  		return 0;
  	}

  	return shrink_inactive_list(nr_to_scan, zone, sc, priority, file);

  }

  static int vmscan_swappiness(struct scan_control *sc)
  {
  	if (scanning_global_lru(sc))
  		return vm_swappiness;
  	return mem_cgroup_swappiness(sc->mem_cgroup);
  }

  /*
   * 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.
   *

   * nr[0] = anon pages to scan; nr[1] = file pages to scan

   */

  static void get_scan_count(struct zone *zone, struct scan_control *sc,
  					unsigned long *nr, int priority)

  {
  	unsigned long anon, file, free;
  	unsigned long anon_prio, file_prio;
  	unsigned long ap, fp;

  	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);

  	u64 fraction[2], denominator;
  	enum lru_list l;
  	int noswap = 0;

  	bool force_scan = false;

  	/*
  	 * 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.
  	 */

  	if (scanning_global_lru(sc) && current_is_kswapd())
  		force_scan = true;

  	if (!scanning_global_lru(sc))
  		force_scan = true;

  
  	/* 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;
  	}

  	anon  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) +
  		zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON);
  	file  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) +
  		zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);

  	if (scanning_global_lru(sc)) {

  		free  = zone_page_state(zone, NR_FREE_PAGES);
  		/* If we have very few page cache pages,
  		   force-scan anon pages. */

  		if (unlikely(file + free <= high_wmark_pages(zone))) {

  			fraction[0] = 1;
  			fraction[1] = 0;
  			denominator = 1;
  			goto out;

  		}

  	}
  
  	/*

  	 * With swappiness at 100, anonymous and file have the same priority.
  	 * This scanning priority is essentially the inverse of IO cost.
  	 */

  	anon_prio = vmscan_swappiness(sc);
  	file_prio = 200 - vmscan_swappiness(sc);