/*
   *  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/vmpressure.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/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 <linux/balloon_compaction.h>

  #include "internal.h"

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

  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;

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

  	/*

  	 * The memory cgroup that hit its limit and as a result is the
  	 * primary target of this reclaim invocation.
  	 */
  	struct mem_cgroup *target_mem_cgroup;

  	/*
  	 * 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;

  unsigned 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_MEMCG

  static bool global_reclaim(struct scan_control *sc)
  {

  	return !sc->target_mem_cgroup;

  }

  #else

  static bool global_reclaim(struct scan_control *sc)
  {
  	return true;
  }

  #endif

  static unsigned long zone_reclaimable_pages(struct zone *zone)

  {
  	int nr;
  
  	nr = zone_page_state(zone, NR_ACTIVE_FILE) +
  	     zone_page_state(zone, NR_INACTIVE_FILE);
  
  	if (get_nr_swap_pages() > 0)
  		nr += zone_page_state(zone, NR_ACTIVE_ANON) +
  		      zone_page_state(zone, NR_INACTIVE_ANON);
  
  	return nr;
  }
  
  bool zone_reclaimable(struct zone *zone)
  {
  	return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
  }

  static unsigned long get_lru_size(struct lruvec *lruvec, enum lru_list lru)

  {

  	if (!mem_cgroup_disabled())

  		return mem_cgroup_get_lru_size(lruvec, lru);

  	return zone_page_state(lruvec_zone(lruvec), NR_LRU_BASE + lru);

  }

  /*

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

   */

  int register_shrinker(struct shrinker *shrinker)

  {

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

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

  	return 0;

  }

  EXPORT_SYMBOL(register_shrinker);

  
  /*
   * Remove one
   */

  void unregister_shrinker(struct shrinker *shrinker)

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

  	kfree(shrinker->nr_deferred);

  }

  EXPORT_SYMBOL(unregister_shrinker);

  
  #define SHRINK_BATCH 128

  
  static unsigned long
  shrink_slab_node(struct shrink_control *shrinkctl, struct shrinker *shrinker,
  		 unsigned long nr_pages_scanned, unsigned long lru_pages)
  {
  	unsigned long freed = 0;
  	unsigned long long delta;
  	long total_scan;
  	long max_pass;
  	long nr;
  	long new_nr;
  	int nid = shrinkctl->nid;
  	long batch_size = shrinker->batch ? shrinker->batch
  					  : SHRINK_BATCH;

  	max_pass = shrinker->count_objects(shrinker, shrinkctl);

  	if (max_pass == 0)
  		return 0;
  
  	/*
  	 * copy the current shrinker scan count into a local variable
  	 * and zero it so that other concurrent shrinker invocations
  	 * don't also do this scanning work.
  	 */
  	nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
  
  	total_scan = nr;
  	delta = (4 * nr_pages_scanned) / shrinker->seeks;
  	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->scan_objects, 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, shrinkctl, nr,
  				nr_pages_scanned, lru_pages,
  				max_pass, delta, total_scan);

  	/*
  	 * Normally, we should not scan less than batch_size objects in one
  	 * pass to avoid too frequent shrinker calls, but if the slab has less
  	 * than batch_size objects in total and we are really tight on memory,
  	 * we will try to reclaim all available objects, otherwise we can end
  	 * up failing allocations although there are plenty of reclaimable
  	 * objects spread over several slabs with usage less than the
  	 * batch_size.
  	 *
  	 * We detect the "tight on memory" situations by looking at the total
  	 * number of objects we want to scan (total_scan). If it is greater
  	 * than the total number of objects on slab (max_pass), we must be
  	 * scanning at high prio and therefore should try to reclaim as much as
  	 * possible.
  	 */
  	while (total_scan >= batch_size ||
  	       total_scan >= max_pass) {

  		unsigned long ret;

  		unsigned long nr_to_scan = min(batch_size, total_scan);

  		shrinkctl->nr_to_scan = nr_to_scan;

  		ret = shrinker->scan_objects(shrinker, shrinkctl);
  		if (ret == SHRINK_STOP)
  			break;
  		freed += ret;

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

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

  }

  /*
   * 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 *shrinkctl,

  			  unsigned long nr_pages_scanned,

  			  unsigned long lru_pages)

  {
  	struct shrinker *shrinker;

  	unsigned long freed = 0;

  	if (nr_pages_scanned == 0)
  		nr_pages_scanned = SWAP_CLUSTER_MAX;

  	if (!down_read_trylock(&shrinker_rwsem)) {

  		/*
  		 * If we would return 0, our callers would understand that we
  		 * have nothing else to shrink and give up trying. By returning
  		 * 1 we keep it going and assume we'll be able to shrink next
  		 * time.
  		 */
  		freed = 1;

  		goto out;
  	}

  
  	list_for_each_entry(shrinker, &shrinker_list, list) {

  		if (!(shrinker->flags & SHRINKER_NUMA_AWARE)) {
  			shrinkctl->nid = 0;

  			freed += shrink_slab_node(shrinkctl, shrinker,

  					nr_pages_scanned, lru_pages);
  			continue;
  		}
  
  		for_each_node_mask(shrinkctl->nid, shrinkctl->nodes_to_scan) {
  			if (node_online(shrinkctl->nid))
  				freed += shrink_slab_node(shrinkctl, shrinker,
  						nr_pages_scanned, lru_pages);

  		}

  	}
  	up_read(&shrinker_rwsem);

  out:
  	cond_resched();

  	return freed;

  }

  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;
  	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));

  		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)
  {

  	bool is_unevictable;

  	int was_unevictable = PageUnevictable(page);

  	VM_BUG_ON_PAGE(PageLRU(page), page);

  
  redo:
  	ClearPageUnevictable(page);

  	if (page_evictable(page)) {

  		/*
  		 * 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.
  		 */

  		is_unevictable = false;

  		lru_cache_add(page);

  	} else {
  		/*
  		 * Put unevictable pages directly on zone's unevictable
  		 * list.
  		 */

  		is_unevictable = true;

  		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_pages,

  		 * 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 (is_unevictable && page_evictable(page)) {

  		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 && !is_unevictable)

  		count_vm_event(UNEVICTABLE_PGRESCUED);

  	else if (!was_unevictable && is_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->target_mem_cgroup,
  					  &vm_flags);

  	referenced_page = TestClearPageReferenced(page);

  	/*
  	 * 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 (PageSwapBacked(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 || referenced_ptes > 1)

  			return PAGEREF_ACTIVATE;

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

  }

  /* Check if a page is dirty or under writeback */
  static void page_check_dirty_writeback(struct page *page,
  				       bool *dirty, bool *writeback)
  {

  	struct address_space *mapping;

  	/*
  	 * Anonymous pages are not handled by flushers and must be written
  	 * from reclaim context. Do not stall reclaim based on them
  	 */
  	if (!page_is_file_cache(page)) {
  		*dirty = false;
  		*writeback = false;
  		return;
  	}
  
  	/* By default assume that the page flags are accurate */
  	*dirty = PageDirty(page);
  	*writeback = PageWriteback(page);

  
  	/* Verify dirty/writeback state if the filesystem supports it */
  	if (!page_has_private(page))
  		return;
  
  	mapping = page_mapping(page);
  	if (mapping && mapping->a_ops->is_dirty_writeback)
  		mapping->a_ops->is_dirty_writeback(page, dirty, writeback);

  }

  /*

   * 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,

  				      enum ttu_flags ttu_flags,

  				      unsigned long *ret_nr_dirty,

  				      unsigned long *ret_nr_unqueued_dirty,

  				      unsigned long *ret_nr_congested,

  				      unsigned long *ret_nr_writeback,

  				      unsigned long *ret_nr_immediate,

  				      bool force_reclaim)

  {
  	LIST_HEAD(ret_pages);

  	LIST_HEAD(free_pages);

  	int pgactivate = 0;

  	unsigned long nr_unqueued_dirty = 0;

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

  	unsigned long nr_reclaimed = 0;

  	unsigned long nr_writeback = 0;

  	unsigned long nr_immediate = 0;

  
  	cond_resched();

  	mem_cgroup_uncharge_start();

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

  		enum page_references references = PAGEREF_RECLAIM_CLEAN;

  		bool dirty, writeback;

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

  		if (!trylock_page(page))

  			goto keep;

  		VM_BUG_ON_PAGE(PageActive(page), page);
  		VM_BUG_ON_PAGE(page_zone(page) != zone, page);

  
  		sc->nr_scanned++;

  		if (unlikely(!page_evictable(page)))

  			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));

  		/*

  		 * The number of dirty pages determines if a zone is marked
  		 * reclaim_congested which affects wait_iff_congested. kswapd
  		 * will stall and start writing pages if the tail of the LRU
  		 * is all dirty unqueued pages.
  		 */
  		page_check_dirty_writeback(page, &dirty, &writeback);
  		if (dirty || writeback)
  			nr_dirty++;
  
  		if (dirty && !writeback)
  			nr_unqueued_dirty++;

  		/*
  		 * Treat this page as congested if the underlying BDI is or if
  		 * pages are cycling through the LRU so quickly that the
  		 * pages marked for immediate reclaim are making it to the
  		 * end of the LRU a second time.
  		 */

  		mapping = page_mapping(page);

  		if ((mapping && bdi_write_congested(mapping->backing_dev_info)) ||
  		    (writeback && PageReclaim(page)))

  			nr_congested++;
  
  		/*

  		 * If a page at the tail of the LRU is under writeback, there
  		 * are three cases to consider.
  		 *
  		 * 1) If reclaim is encountering an excessive number of pages
  		 *    under writeback and this page is both under writeback and
  		 *    PageReclaim then it indicates that pages are being queued
  		 *    for IO but are being recycled through the LRU before the
  		 *    IO can complete. Waiting on the page itself risks an
  		 *    indefinite stall if it is impossible to writeback the
  		 *    page due to IO error or disconnected storage so instead

  		 *    note that the LRU is being scanned too quickly and the
  		 *    caller can stall after page list has been processed.

  		 *
  		 * 2) Global reclaim encounters a page, memcg encounters a
  		 *    page that is not marked for immediate reclaim or
  		 *    the caller does not have __GFP_IO. In this case mark
  		 *    the page for immediate reclaim and continue scanning.
  		 *
  		 *    __GFP_IO is checked  because a loop driver thread might
  		 *    enter reclaim, and deadlock if it waits on a page for
  		 *    which it is needed to do the write (loop masks off
  		 *    __GFP_IO|__GFP_FS for this reason); but more thought
  		 *    would probably show more reasons.
  		 *
  		 *    Don't require __GFP_FS, since we're not going into the
  		 *    FS, just waiting on its writeback completion. Worryingly,
  		 *    ext4 gfs2 and xfs allocate pages with
  		 *    grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so testing
  		 *    may_enter_fs here is liable to OOM on them.
  		 *
  		 * 3) memcg encounters a page that is not already marked
  		 *    PageReclaim. memcg does not have any dirty pages
  		 *    throttling so we could easily OOM just because too many
  		 *    pages are in writeback and there is nothing else to
  		 *    reclaim. Wait for the writeback to complete.
  		 */

  		if (PageWriteback(page)) {

  			/* Case 1 above */
  			if (current_is_kswapd() &&
  			    PageReclaim(page) &&
  			    zone_is_reclaim_writeback(zone)) {

  				nr_immediate++;
  				goto keep_locked;

  
  			/* Case 2 above */
  			} else if (global_reclaim(sc) ||

  			    !PageReclaim(page) || !(sc->gfp_mask & __GFP_IO)) {
  				/*
  				 * This is slightly racy - end_page_writeback()
  				 * might have just cleared PageReclaim, then
  				 * setting PageReclaim here end up interpreted
  				 * as PageReadahead - but that does not matter
  				 * enough to care.  What we do want is for this
  				 * page to have PageReclaim set next time memcg
  				 * reclaim reaches the tests above, so it will
  				 * then wait_on_page_writeback() to avoid OOM;
  				 * and it's also appropriate in global reclaim.
  				 */
  				SetPageReclaim(page);

  				nr_writeback++;

  				goto keep_locked;

  
  			/* Case 3 above */
  			} else {
  				wait_on_page_writeback(page);

  			}

  		}

  		if (!force_reclaim)
  			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, page_list))

  				goto activate_locked;

  			may_enter_fs = 1;

  			/* Adding to swap updated mapping */
  			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_flags)) {

  			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)) {

  			/*
  			 * Only kswapd can writeback filesystem pages to

  			 * avoid risk of stack overflow but only writeback
  			 * if many dirty pages have been encountered.

  			 */

  			if (page_is_file_cache(page) &&

  					(!current_is_kswapd() ||

  					 !zone_is_reclaim_dirty(zone))) {

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

  				if (PageWriteback(page))

  					goto keep;

  				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);
  		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_PAGE(PageActive(page), page);

  		SetPageActive(page);
  		pgactivate++;
  keep_locked:
  		unlock_page(page);
  keep:
  		list_add(&page->lru, &ret_pages);

  		VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page);

  	}

  	free_hot_cold_page_list(&free_pages, 1);

  	list_splice(&ret_pages, page_list);

  	count_vm_events(PGACTIVATE, pgactivate);

  	mem_cgroup_uncharge_end();

  	*ret_nr_dirty += nr_dirty;
  	*ret_nr_congested += nr_congested;

  	*ret_nr_unqueued_dirty += nr_unqueued_dirty;

  	*ret_nr_writeback += nr_writeback;

  	*ret_nr_immediate += nr_immediate;

  	return nr_reclaimed;

  }

  unsigned long reclaim_clean_pages_from_list(struct zone *zone,
  					    struct list_head *page_list)
  {
  	struct scan_control sc = {
  		.gfp_mask = GFP_KERNEL,
  		.priority = DEF_PRIORITY,
  		.may_unmap = 1,
  	};

  	unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5;

  	struct page *page, *next;
  	LIST_HEAD(clean_pages);
  
  	list_for_each_entry_safe(page, next, page_list, lru) {

  		if (page_is_file_cache(page) && !PageDirty(page) &&
  		    !isolated_balloon_page(page)) {

  			ClearPageActive(page);
  			list_move(&page->lru, &clean_pages);
  		}
  	}
  
  	ret = shrink_page_list(&clean_pages, zone, &sc,

  			TTU_UNMAP|TTU_IGNORE_ACCESS,
  			&dummy1, &dummy2, &dummy3, &dummy4, &dummy5, true);

  	list_splice(&clean_pages, page_list);
  	__mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret);
  	return ret;
  }

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

  	/* Compaction should not handle unevictable pages but CMA can do so */
  	if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))

  		return ret;

  	ret = -EBUSY;

  	/*
  	 * To minimise LRU disruption, the caller can indicate that it only
  	 * wants to isolate pages it will be able to operate on without
  	 * blocking - clean pages for the most part.
  	 *
  	 * ISOLATE_CLEAN means that only clean pages should be isolated. This
  	 * is used by reclaim when it is cannot write to backing storage
  	 *
  	 * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
  	 * that it is possible to migrate without blocking
  	 */
  	if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) {
  		/* All the caller can do on PageWriteback is block */
  		if (PageWriteback(page))
  			return ret;
  
  		if (PageDirty(page)) {
  			struct address_space *mapping;
  
  			/* ISOLATE_CLEAN means only clean pages */
  			if (mode & ISOLATE_CLEAN)
  				return ret;
  
  			/*
  			 * Only pages without mappings or that have a
  			 * ->migratepage callback are possible to migrate
  			 * without blocking
  			 */
  			mapping = page_mapping(page);
  			if (mapping && !mapping->a_ops->migratepage)
  				return ret;
  		}
  	}

  	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.

   * @lruvec:	The LRU vector to pull pages from.

   * @dst:	The temp list to put pages on to.

   * @nr_scanned:	The number of pages that were scanned.

   * @sc:		The scan_control struct for this reclaim session

   * @mode:	One of the LRU isolation modes

   * @lru:	LRU list id for isolating

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

  static unsigned long isolate_lru_pages(unsigned long nr_to_scan,

  		struct lruvec *lruvec, struct list_head *dst,

  		unsigned long *nr_scanned, struct scan_control *sc,

  		isolate_mode_t mode, enum lru_list lru)

  {

  	struct list_head *src = &lruvec->lists[lru];

  	unsigned long nr_taken = 0;

  	unsigned long scan;

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

  		struct page *page;

  		int nr_pages;

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

  		VM_BUG_ON_PAGE(!PageLRU(page), page);

  		switch (__isolate_lru_page(page, mode)) {

  		case 0:

  			nr_pages = hpage_nr_pages(page);
  			mem_cgroup_update_lru_size(lruvec, lru, -nr_pages);

  			list_move(&page->lru, dst);

  			nr_taken += nr_pages;

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

  		default:
  			BUG();
  		}

  	}

  	*nr_scanned = scan;

  	trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
  				    nr_taken, mode, is_file_lru(lru));

  	return nr_taken;
  }

  /**
   * 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(!page_count(page), page);

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

  		struct lruvec *lruvec;

  
  		spin_lock_irq(&zone->lru_lock);

  		lruvec = mem_cgroup_page_lruvec(page, zone);

  		if (PageLRU(page)) {

  			int lru = page_lru(page);

  			get_page(page);

  			ClearPageLRU(page);

  			del_page_from_lru_list(page, lruvec, lru);
  			ret = 0;

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

  /*

   * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
   * then get resheduled. When there are massive number of tasks doing page
   * allocation, such sleeping direct reclaimers may keep piling up on each CPU,
   * the LRU list will go small and be scanned faster than necessary, leading to
   * unnecessary swapping, thrashing and OOM.

   */
  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 (!global_reclaim(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);
  	}

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

  	return isolated > inactive;
  }

  static noinline_for_stack void

  putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)

  {

  	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
  	struct zone *zone = lruvec_zone(lruvec);

  	LIST_HEAD(pages_to_free);

  	/*
  	 * Put back any unfreeable pages.
  	 */

  	while (!list_empty(page_list)) {

  		struct page *page = lru_to_page(page_list);

  		int lru;

  		VM_BUG_ON_PAGE(PageLRU(page), page);

  		list_del(&page->lru);

  		if (unlikely(!page_evictable(page))) {

  			spin_unlock_irq(&zone->lru_lock);
  			putback_lru_page(page);
  			spin_lock_irq(&zone->lru_lock);
  			continue;
  		}

  
  		lruvec = mem_cgroup_page_lruvec(page, zone);

  		SetPageLRU(page);

  		lru = page_lru(page);

  		add_page_to_lru_list(page, lruvec, 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 (put_page_testzero(page)) {
  			__ClearPageLRU(page);
  			__ClearPageActive(page);

  			del_page_from_lru_list(page, lruvec, lru);

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

  		}
  	}

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

  }
  
  /*

   * 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 lruvec *lruvec,

  		     struct scan_control *sc, enum lru_list lru)

  {
  	LIST_HEAD(page_list);

  	unsigned long nr_scanned;

  	unsigned long nr_reclaimed = 0;

  	unsigned long nr_taken;

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

  	unsigned long nr_unqueued_dirty = 0;

  	unsigned long nr_writeback = 0;

  	unsigned long nr_immediate = 0;

  	isolate_mode_t isolate_mode = 0;

  	int file = is_file_lru(lru);

  	struct zone *zone = lruvec_zone(lruvec);
  	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;

  	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;
  	}

  	lru_add_drain();

  
  	if (!sc->may_unmap)

  		isolate_mode |= ISOLATE_UNMAPPED;

  	if (!sc->may_writepage)

  		isolate_mode |= ISOLATE_CLEAN;

  	spin_lock_irq(&zone->lru_lock);

  	nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
  				     &nr_scanned, sc, isolate_mode, lru);

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

  	if (global_reclaim(sc)) {

  		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);

  	}

  	spin_unlock_irq(&zone->lru_lock);

  	if (nr_taken == 0)

  		return 0;

  	nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,

  				&nr_dirty, &nr_unqueued_dirty, &nr_congested,
  				&nr_writeback, &nr_immediate,
  				false);

  	spin_lock_irq(&zone->lru_lock);

  	reclaim_stat->recent_scanned[file] += nr_taken;

  	if (global_reclaim(sc)) {
  		if (current_is_kswapd())
  			__count_zone_vm_events(PGSTEAL_KSWAPD, zone,
  					       nr_reclaimed);
  		else
  			__count_zone_vm_events(PGSTEAL_DIRECT, zone,
  					       nr_reclaimed);
  	}

  	putback_inactive_pages(lruvec, &page_list);

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

  
  	spin_unlock_irq(&zone->lru_lock);
  
  	free_hot_cold_page_list(&page_list, 1);

  	/*
  	 * 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.
  	 *

  	 * Once a zone is flagged ZONE_WRITEBACK, kswapd will count the number
  	 * of pages under pages flagged for immediate reclaim and stall if any
  	 * are encountered in the nr_immediate check below.

  	 */

  	if (nr_writeback && nr_writeback == nr_taken)

  		zone_set_flag(zone, ZONE_WRITEBACK);

  	/*

  	 * memcg will stall in page writeback so only consider forcibly
  	 * stalling for global reclaim

  	 */

  	if (global_reclaim(sc)) {
  		/*

  		 * Tag a zone as congested if all the dirty pages scanned were
  		 * backed by a congested BDI and wait_iff_congested will stall.
  		 */
  		if (nr_dirty && nr_dirty == nr_congested)
  			zone_set_flag(zone, ZONE_CONGESTED);
  
  		/*

  		 * If dirty pages are scanned that are not queued for IO, it
  		 * implies that flushers are not keeping up. In this case, flag
  		 * the zone ZONE_TAIL_LRU_DIRTY and kswapd will start writing
  		 * pages from reclaim context. It will forcibly stall in the
  		 * next check.
  		 */
  		if (nr_unqueued_dirty == nr_taken)
  			zone_set_flag(zone, ZONE_TAIL_LRU_DIRTY);
  
  		/*
  		 * In addition, if kswapd scans pages marked marked for
  		 * immediate reclaim and under writeback (nr_immediate), it
  		 * implies that pages are cycling through the LRU faster than
  		 * they are written so also forcibly stall.
  		 */
  		if (nr_unqueued_dirty == nr_taken || nr_immediate)
  			congestion_wait(BLK_RW_ASYNC, HZ/10);

  	}

  	/*
  	 * Stall direct reclaim for IO completions if underlying BDIs or zone
  	 * is congested. Allow kswapd to continue until it starts encountering
  	 * unqueued dirty pages or cycling through the LRU too quickly.
  	 */
  	if (!sc->hibernation_mode && !current_is_kswapd())
  		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,

  		sc->priority,

  		trace_shrink_flags(file));

  	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 lruvec *lruvec,

  				     struct list_head *list,

  				     struct list_head *pages_to_free,

  				     enum lru_list lru)
  {

  	struct zone *zone = lruvec_zone(lruvec);

  	unsigned long pgmoved = 0;

  	struct page *page;

  	int nr_pages;

  	while (!list_empty(list)) {
  		page = lru_to_page(list);

  		lruvec = mem_cgroup_page_lruvec(page, zone);

  		VM_BUG_ON_PAGE(PageLRU(page), page);

  		SetPageLRU(page);

  		nr_pages = hpage_nr_pages(page);
  		mem_cgroup_update_lru_size(lruvec, lru, nr_pages);

  		list_move(&page->lru, &lruvec->lists[lru]);

  		pgmoved += nr_pages;

  		if (put_page_testzero(page)) {
  			__ClearPageLRU(page);
  			__ClearPageActive(page);

  			del_page_from_lru_list(page, lruvec, lru);

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

  		}
  	}
  	__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_to_scan,

  			       struct lruvec *lruvec,

  			       struct scan_control *sc,

  			       enum lru_list lru)

  {

  	unsigned long nr_taken;

  	unsigned long nr_scanned;

  	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 = &lruvec->reclaim_stat;

  	unsigned long nr_rotated = 0;

  	isolate_mode_t isolate_mode = 0;

  	int file = is_file_lru(lru);

  	struct zone *zone = lruvec_zone(lruvec);

  
  	lru_add_drain();

  
  	if (!sc->may_unmap)

  		isolate_mode |= ISOLATE_UNMAPPED;

  	if (!sc->may_writepage)

  		isolate_mode |= ISOLATE_CLEAN;

  	spin_lock_irq(&zone->lru_lock);

  	nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
  				     &nr_scanned, sc, isolate_mode, lru);

  	if (global_reclaim(sc))

  		zone->pages_scanned += nr_scanned;

  	reclaim_stat->recent_scanned[file] += nr_taken;

  	__count_zone_vm_events(PGREFILL, zone, nr_scanned);

  	__mod_zone_page_state(zone, NR_LRU_BASE + lru, -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))) {

  			putback_lru_page(page);
  			continue;
  		}

  		if (unlikely(buffer_heads_over_limit)) {
  			if (page_has_private(page) && trylock_page(page)) {
  				if (page_has_private(page))
  					try_to_release_page(page, 0);
  				unlock_page(page);
  			}
  		}

  		if (page_referenced(page, 0, sc->target_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(lruvec, &l_active, &l_hold, lru);
  	move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);

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

  	spin_unlock_irq(&zone->lru_lock);

  
  	free_hot_cold_page_list(&l_hold, 1);

  }

  #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

   * @lruvec: LRU vector to check

   *
   * 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 lruvec *lruvec)

  {

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

  	if (!mem_cgroup_disabled())

  		return mem_cgroup_inactive_anon_is_low(lruvec);

  	return inactive_anon_is_low_global(lruvec_zone(lruvec));

  }

  #else