/*
   *  linux/mm/vmscan.c
   *
   *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
   *
   *  Swap reorganised 29.12.95, Stephen Tweedie.
   *  kswapd added: 7.1.96  sct
   *  Removed kswapd_ctl limits, and swap out as many pages as needed
   *  to bring the system back to freepages.high: 2.4.97, Rik van Riel.
   *  Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
   *  Multiqueue VM started 5.8.00, Rik van Riel.
   */
  
  #include <linux/mm.h>
  #include <linux/module.h>
  #include <linux/slab.h>
  #include <linux/kernel_stat.h>
  #include <linux/swap.h>
  #include <linux/pagemap.h>
  #include <linux/init.h>
  #include <linux/highmem.h>

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

  #include "internal.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 swappiness;

  
  	int all_unreclaimable;

  
  	int order;

  
  	/* 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;

  	/* Pluggable isolate pages callback */
  	unsigned long (*isolate_pages)(unsigned long nr, struct list_head *dst,
  			unsigned long *scanned, int order, int mode,
  			struct zone *z, struct mem_cgroup *mem_cont,

  			int active, int file);

  };

  #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_pages(sc->mem_cgroup, zone, 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)

  {

  	shrinker->nr = 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);

  
  #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(unsigned long scanned, gfp_t gfp_mask,
  			unsigned long lru_pages)

  {
  	struct shrinker *shrinker;

  	unsigned long ret = 0;

  
  	if (scanned == 0)
  		scanned = SWAP_CLUSTER_MAX;
  
  	if (!down_read_trylock(&shrinker_rwsem))

  		return 1;	/* Assume we'll be able to shrink next time */

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

  		unsigned long max_pass = (*shrinker->shrink)(0, gfp_mask);

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

  		delta *= max_pass;

  		do_div(delta, lru_pages + 1);
  		shrinker->nr += delta;

  		if (shrinker->nr < 0) {

  			printk(KERN_ERR "shrink_slab: %pF negative objects to "
  			       "delete nr=%ld
  ",
  			       shrinker->shrink, shrinker->nr);

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

  
  		total_scan = shrinker->nr;
  		shrinker->nr = 0;
  
  		while (total_scan >= SHRINK_BATCH) {
  			long this_scan = SHRINK_BATCH;
  			int shrink_ret;

  			int nr_before;

  			nr_before = (*shrinker->shrink)(0, gfp_mask);
  			shrink_ret = (*shrinker->shrink)(this_scan, gfp_mask);

  			if (shrink_ret == -1)
  				break;

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

  			count_vm_events(SLABS_SCANNED, this_scan);

  			total_scan -= this_scan;
  
  			cond_resched();
  		}
  
  		shrinker->nr += total_scan;
  	}
  	up_read(&shrinker_rwsem);

  	return ret;

  }

  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)
  {

  	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);
  }

  /* Request for sync pageout. */
  enum pageout_io {
  	PAGEOUT_IO_ASYNC,
  	PAGEOUT_IO_SYNC,
  };

  /* 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,
  						enum pageout_io sync_writeback)

  {
  	/*
  	 * 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))
  		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,

  			.nonblocking = 1,
  			.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;
  		}

  
  		/*
  		 * Wait on writeback if requested to. This happens when
  		 * direct reclaiming a large contiguous area and the
  		 * first attempt to free a range of pages fails.
  		 */
  		if (PageWriteback(page) && sync_writeback == PAGEOUT_IO_SYNC)
  			wait_on_page_writeback(page);

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

  		spin_unlock_irq(&mapping->tree_lock);

  		mem_cgroup_uncharge_cache_page(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 clearing (page is
  		 * unlocked), make sure that if the other thread does
  		 * not observe our setting of PG_lru and fails
  		 * isolation, we see PG_mlocked cleared below and move
  		 * the page back to the evictable list.
  		 *
  		 * The other side is TestClearPageMlocked().
  		 */
  		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->order > PAGE_ALLOC_COSTLY_ORDER)
  		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)
  		return PAGEREF_RECLAIM_CLEAN;
  
  	return PAGEREF_RECLAIM;

  }

  /*

   * shrink_page_list() returns the number of reclaimed pages

   */

  static unsigned long shrink_page_list(struct list_head *page_list,

  					struct scan_control *sc,
  					enum pageout_io sync_writeback)

  {
  	LIST_HEAD(ret_pages);
  	struct pagevec freed_pvec;
  	int pgactivate = 0;

  	unsigned long nr_reclaimed = 0;

  
  	cond_resched();
  
  	pagevec_init(&freed_pvec, 1);
  	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));

  
  		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)) {
  			/*
  			 * Synchronous reclaim is performed in two passes,
  			 * first an asynchronous pass over the list to
  			 * start parallel writeback, and a second synchronous
  			 * pass to wait for the IO to complete.  Wait here
  			 * for any page for which writeback has already
  			 * started.
  			 */
  			if (sync_writeback == PAGEOUT_IO_SYNC && may_enter_fs)
  				wait_on_page_writeback(page);

  			else

  				goto keep_locked;
  		}

  		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)) {

  			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, sync_writeback)) {

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

  				if (PageWriteback(page) || PageDirty(page))

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

  				if (!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++;

  		if (!pagevec_add(&freed_pvec, page)) {
  			__pagevec_free(&freed_pvec);
  			pagevec_reinit(&freed_pvec);
  		}

  		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(PageActive(page));

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

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

  	}
  	list_splice(&ret_pages, page_list);
  	if (pagevec_count(&freed_pvec))

  		__pagevec_free(&freed_pvec);

  	count_vm_events(PGACTIVATE, pgactivate);

  	return nr_reclaimed;

  }

  /* LRU Isolation modes. */
  #define ISOLATE_INACTIVE 0	/* Isolate inactive pages. */
  #define ISOLATE_ACTIVE 1	/* Isolate active pages. */
  #define ISOLATE_BOTH 2		/* Isolate both active and inactive pages. */
  
  /*
   * 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, int mode, int file)

  {
  	int ret = -EINVAL;
  
  	/* Only take pages on the LRU. */
  	if (!PageLRU(page))
  		return ret;
  
  	/*
  	 * When checking the active state, we need to be sure we are
  	 * dealing with comparible boolean values.  Take the logical not
  	 * of each.
  	 */
  	if (mode != ISOLATE_BOTH && (!PageActive(page) != !mode))
  		return ret;

  	if (mode != ISOLATE_BOTH && 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 (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, int mode, int file)

  {

  	unsigned long nr_taken = 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++;

  			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 guarenteed 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))
  				continue;

  
  			/*
  			 * 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))
  				continue;

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

  				list_move(&cursor_page->lru, dst);

  				mem_cgroup_del_lru(cursor_page);

  				nr_taken++;
  				scan++;

  			}
  		}

  	}
  
  	*scanned = scan;
  	return nr_taken;
  }

  static unsigned long isolate_pages_global(unsigned long nr,
  					struct list_head *dst,
  					unsigned long *scanned, int order,
  					int mode, struct zone *z,
  					struct mem_cgroup *mem_cont,

  					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) {

  		lru = page_lru_base_type(page);

  		if (PageActive(page)) {

  			lru += LRU_ACTIVE;

  			ClearPageActive(page);
  			nr_active++;
  		}

  		count[lru]++;
  	}

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

  			int lru = page_lru(page);

  			ret = 0;
  			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;
  }
  
  /*

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

   */

  static unsigned long shrink_inactive_list(unsigned long max_scan,

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

  {
  	LIST_HEAD(page_list);
  	struct pagevec pvec;

  	unsigned long nr_scanned = 0;

  	unsigned long nr_reclaimed = 0;

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

  	int lumpy_reclaim = 0;

  	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;
  	}

  	/*
  	 * If we need a large contiguous chunk of memory, or have
  	 * trouble getting a small set of contiguous pages, we
  	 * will reclaim both active and inactive pages.
  	 *
  	 * We use the same threshold as pageout congestion_wait below.
  	 */
  	if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
  		lumpy_reclaim = 1;
  	else if (sc->order && priority < DEF_PRIORITY - 2)
  		lumpy_reclaim = 1;

  
  	pagevec_init(&pvec, 1);
  
  	lru_add_drain();
  	spin_lock_irq(&zone->lru_lock);

  	do {

  		struct page *page;

  		unsigned long nr_taken;
  		unsigned long nr_scan;
  		unsigned long nr_freed;

  		unsigned long nr_active;

  		unsigned int count[NR_LRU_LISTS] = { 0, };

  		int mode = lumpy_reclaim ? ISOLATE_BOTH : ISOLATE_INACTIVE;

  		unsigned long nr_anon;
  		unsigned long nr_file;

  		nr_taken = sc->isolate_pages(SWAP_CLUSTER_MAX,

  			     &page_list, &nr_scan, sc->order, mode,
  				zone, sc->mem_cgroup, 0, file);

  
  		if (scanning_global_lru(sc)) {
  			zone->pages_scanned += nr_scan;
  			if (current_is_kswapd())
  				__count_zone_vm_events(PGSCAN_KSWAPD, zone,
  						       nr_scan);
  			else
  				__count_zone_vm_events(PGSCAN_DIRECT, zone,
  						       nr_scan);
  		}
  
  		if (nr_taken == 0)
  			goto done;

  		nr_active = clear_active_flags(&page_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;

  		spin_unlock_irq(&zone->lru_lock);

  		nr_scanned += nr_scan;

  		nr_freed = shrink_page_list(&page_list, sc, PAGEOUT_IO_ASYNC);
  
  		/*
  		 * If we are direct reclaiming for contiguous pages and we do
  		 * not reclaim everything in the list, try again and wait
  		 * for IO to complete. This will stall high-order allocations
  		 * but that should be acceptable to the caller
  		 */
  		if (nr_freed < nr_taken && !current_is_kswapd() &&

  		    lumpy_reclaim) {

  			congestion_wait(BLK_RW_ASYNC, HZ/10);

  
  			/*
  			 * The attempt at page out may have made some
  			 * of the pages active, mark them inactive again.
  			 */

  			nr_active = clear_active_flags(&page_list, count);

  			count_vm_events(PGDEACTIVATE, nr_active);
  
  			nr_freed += shrink_page_list(&page_list, sc,
  							PAGEOUT_IO_SYNC);
  		}

  		nr_reclaimed += nr_freed;

  		local_irq_disable();

  		if (current_is_kswapd())

  			__count_vm_events(KSWAPD_STEAL, nr_freed);

  		__count_zone_vm_events(PGSTEAL, zone, nr_freed);

  
  		spin_lock(&zone->lru_lock);

  		/*
  		 * Put back any unfreeable pages.
  		 */
  		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);

  				reclaim_stat->recent_rotated[file]++;

  			}

  			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);

    	} while (nr_scanned < max_scan);

  done:

  	spin_unlock_irq(&zone->lru_lock);

  	pagevec_release(&pvec);

  	return nr_reclaimed;

  }

  /*
   * We are about to scan this zone at a certain priority level.  If that priority
   * level is smaller (ie: more urgent) than the previous priority, then note
   * that priority level within the zone.  This is done so that when the next
   * process comes in to scan this zone, it will immediately start out at this
   * priority level rather than having to build up its own scanning priority.
   * Here, this priority affects only the reclaim-mapped threshold.
   */
  static inline void note_zone_scanning_priority(struct zone *zone, int priority)
  {
  	if (priority < zone->prev_priority)
  		zone->prev_priority = priority;
  }

  /*

   * 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++;
  
  		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;

  
  	lru_add_drain();
  	spin_lock_irq(&zone->lru_lock);

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

  					ISOLATE_ACTIVE, zone,

  					sc->mem_cgroup, 1, file);

  	/*
  	 * zone->pages_scanned is used for detect zone's oom
  	 * mem_cgroup remembers nr_scan by itself.
  	 */

  	if (scanning_global_lru(sc)) {

  		zone->pages_scanned += pgscanned;

  	}

  	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++;

  			/*
  			 * 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);

  }

  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 (scanning_global_lru(sc))

  		low = inactive_anon_is_low_global(zone);
  	else

  		low = mem_cgroup_inactive_anon_is_low(sc->mem_cgroup);

  	return low;
  }

  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);
  	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);

  }
  
  /*
   * 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.
   *
   * percent[0] specifies how much pressure to put on ram/swap backed
   * memory, while percent[1] determines pressure on the file LRUs.
   */
  static void get_scan_ratio(struct zone *zone, struct scan_control *sc,
  					unsigned long *percent)
  {
  	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);

  	/* If we have no swap space, do not bother scanning anon pages. */
  	if (!sc->may_swap || (nr_swap_pages <= 0)) {
  		percent[0] = 0;
  		percent[1] = 100;
  		return;
  	}

  	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))) {

  			percent[0] = 100;
  			percent[1] = 0;
  			return;
  		}

  	}
  
  	/*
  	 * OK, so we have swap space and a fair amount of page cache
  	 * pages.  We use the recently rotated / recently scanned
  	 * ratios to determine how valuable each cache is.
  	 *
  	 * Because workloads change over time (and to avoid overflow)
  	 * we keep these statistics as a floating average, which ends
  	 * up weighing recent references more than old ones.
  	 *
  	 * anon in [0], file in [1]
  	 */

  	if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {

  		spin_lock_irq(&zone->lru_lock);

  		reclaim_stat->recent_scanned[0] /= 2;
  		reclaim_stat->recent_rotated[0] /= 2;

  		spin_unlock_irq(&zone->lru_lock);
  	}

  	if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {

  		spin_lock_irq(&zone->lru_lock);

  		reclaim_stat->recent_scanned[1] /= 2;
  		reclaim_stat->recent_rotated[1] /= 2;

  		spin_unlock_irq(&zone->lru_lock);
  	}
  
  	/*
  	 * With swappiness at 100, anonymous and file have the same priority.
  	 * This scanning priority is essentially the inverse of IO cost.
  	 */
  	anon_prio = sc->swappiness;
  	file_prio = 200 - sc->swappiness;
  
  	/*

  	 * The amount of pressure on anon vs file pages is inversely
  	 * proportional to the fraction of recently scanned pages on
  	 * each list that were recently referenced and in active use.

  	 */

  	ap = (anon_prio + 1) * (reclaim_stat->recent_scanned[0] + 1);
  	ap /= reclaim_stat->recent_rotated[0] + 1;

  	fp = (file_prio + 1) * (reclaim_stat->recent_scanned[1] + 1);
  	fp /= reclaim_stat->recent_rotated[1] + 1;

  
  	/* Normalize to percentages */
  	percent[0] = 100 * ap / (ap + fp + 1);
  	percent[1] = 100 - percent[0];

  }

  /*
   * Smallish @nr_to_scan's are deposited in @nr_saved_scan,
   * until we collected @swap_cluster_max pages to scan.
   */
  static unsigned long nr_scan_try_batch(unsigned long nr_to_scan,

  				       unsigned long *nr_saved_scan)

  {
  	unsigned long nr;
  
  	*nr_saved_scan += nr_to_scan;
  	nr = *nr_saved_scan;

  	if (nr >= SWAP_CLUSTER_MAX)

  		*nr_saved_scan = 0;
  	else
  		nr = 0;
  
  	return nr;
  }

  /*
   * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
   */

  static void shrink_zone(int priority, struct zone *zone,

  				struct scan_control *sc)

  {

  	unsigned long nr[NR_LRU_LISTS];

  	unsigned long nr_to_scan;

  	unsigned long percent[2];	/* anon @ 0; file @ 1 */

  	enum lru_list l;

  	unsigned long nr_reclaimed = sc->nr_reclaimed;

  	unsigned long nr_to_reclaim = sc->nr_to_reclaim;

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

  	get_scan_ratio(zone, sc, percent);

  	for_each_evictable_lru(l) {

  		int file = is_file_lru(l);

  		unsigned long scan;

  		if (percent[file] == 0) {
  			nr[l] = 0;
  			continue;
  		}

  		scan = zone_nr_lru_pages(zone, sc, l);

  		if (priority) {

  			scan >>= priority;
  			scan = (scan * percent[file]) / 100;
  		}

  		nr[l] = nr_scan_try_batch(scan,

  					  &reclaim_stat->nr_saved_scan[l]);

  	}

  	while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
  					nr[LRU_INACTIVE_FILE]) {

  		for_each_evictable_lru(l) {

  			if (nr[l]) {

  				nr_to_scan = min_t(unsigned long,
  						   nr[l], SWAP_CLUSTER_MAX);

  				nr[l] -= nr_to_scan;

  				nr_reclaimed += shrink_list(l, nr_to_scan,
  							    zone, sc, priority);

  			}

  		}

  		/*
  		 * On large memory systems, scan >> priority can become
  		 * really large. This is fine for the starting priority;
  		 * we want to put equal scanning pressure on each zone.
  		 * However, if the VM has a harder time of freeing pages,
  		 * with multiple processes reclaiming pages, the total
  		 * freeing target can get unreasonably large.
  		 */

  		if (nr_reclaimed >= nr_to_reclaim && priority < DEF_PRIORITY)

  			break;

  	}

  	sc->nr_reclaimed = nr_reclaimed;

  	/*
  	 * Even if we did not try to evict anon pages at all, we want to
  	 * rebalance the anon lru active/inactive ratio.
  	 */

  	if (inactive_anon_is_low(zone, sc) && nr_swap_pages > 0)

  		shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0);

  	throttle_vm_writeout(sc->gfp_mask);

  }
  
  /*
   * This is the direct reclaim path, for page-allocating processes.  We only
   * try to reclaim pages from zones which will satisfy the caller's allocation
   * request.
   *

   * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
   * Because:

   * a) The caller may be trying to free *extra* pages to satisfy a higher-order
   *    allocation or

   * b) The target zone may be at high_wmark_pages(zone) but the lower zones
   *    must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
   *    zone defense algorithm.

   *

   * If a zone is deemed to be full of pinned pages then just give it a light
   * scan then give up on it.
   */

  static void shrink_zones(int priority, struct zonelist *zonelist,

  					struct scan_control *sc)

  {

  	enum zone_type high_zoneidx = gfp_zone(sc->gfp_mask);

  	struct zoneref *z;

  	struct zone *zone;

  	sc->all_unreclaimable = 1;

  	for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
  					sc->nodemask) {

  		if (!populated_zone(zone))

  			continue;

  		/*
  		 * Take care memory controller reclaiming has small influence
  		 * to global LRU.
  		 */

  		if (scanning_global_lru(sc)) {

  			if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
  				continue;
  			note_zone_scanning_priority(zone, priority);

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

  				continue;	/* Let kswapd poll it */
  			sc->all_unreclaimable = 0;
  		} else {
  			/*
  			 * Ignore cpuset limitation here. We just want to reduce
  			 * # of used pages by us regardless of memory shortage.
  			 */
  			sc->all_unreclaimable = 0;
  			mem_cgroup_note_reclaim_priority(sc->mem_cgroup,
  							priority);
  		}

  		shrink_zone(priority, zone, sc);

  	}
  }

  /*
   * This is the main entry point to direct page reclaim.
   *
   * If a full scan of the inactive list fails to free enough memory then we
   * are "out of memory" and something needs to be killed.
   *
   * If the caller is !__GFP_FS then the probability of a failure is reasonably
   * high - the zone may be full of dirty or under-writeback pages, which this

   * caller can't do much about.  We kick the writeback threads and take explicit
   * naps in the hope that some of these pages can be written.  But if the
   * allocating task holds filesystem locks which prevent writeout this might not
   * work, and the allocation attempt will fail.

   *
   * returns:	0, if no pages reclaimed
   * 		else, the number of pages reclaimed

   */

  static unsigned long do_try_to_free_pages(struct zonelist *zonelist,

  					struct scan_control *sc)

  {
  	int priority;

  	unsigned long ret = 0;

  	unsigned long total_scanned = 0;

  	struct reclaim_state *reclaim_state = current->reclaim_state;

  	unsigned long lru_pages = 0;

  	struct zoneref *z;

  	struct zone *zone;

  	enum zone_type high_zoneidx = gfp_zone(sc->gfp_mask);

  	unsigned long writeback_threshold;

  	delayacct_freepages_start();

  	if (scanning_global_lru(sc))

  		count_vm_event(ALLOCSTALL);
  	/*
  	 * mem_cgroup will not do shrink_slab.
  	 */

  	if (scanning_global_lru(sc)) {

  		for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {

  			if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
  				continue;

  			lru_pages += zone_reclaimable_pages(zone);

  		}

  	}
  
  	for (priority = DEF_PRIORITY; priority >= 0; priority--) {

  		sc->nr_scanned = 0;

  		if (!priority)
  			disable_swap_token();

  		shrink_zones(priority, zonelist, sc);

  		/*
  		 * Don't shrink slabs when reclaiming memory from
  		 * over limit cgroups
  		 */

  		if (scanning_global_lru(sc)) {

  			shrink_slab(sc->nr_scanned, sc->gfp_mask, lru_pages);

  			if (reclaim_state) {

  				sc->nr_reclaimed += reclaim_state->reclaimed_slab;

  				reclaim_state->reclaimed_slab = 0;
  			}

  		}

  		total_scanned += sc->nr_scanned;

  		if (sc->nr_reclaimed >= sc->nr_to_reclaim) {

  			ret = sc->nr_reclaimed;

  			goto out;
  		}
  
  		/*
  		 * Try to write back as many pages as we just scanned.  This
  		 * tends to cause slow streaming writers to write data to the
  		 * disk smoothly, at the dirtying rate, which is nice.   But
  		 * that's undesirable in laptop mode, where we *want* lumpy
  		 * writeout.  So in laptop mode, write out the whole world.
  		 */

  		writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
  		if (total_scanned > writeback_threshold) {

  			wakeup_flusher_threads(laptop_mode ? 0 : total_scanned);

  			sc->may_writepage = 1;

  		}
  
  		/* Take a nap, wait for some writeback to complete */

  		if (!sc->hibernation_mode && sc->nr_scanned &&
  		    priority < DEF_PRIORITY - 2)

  			congestion_wait(BLK_RW_ASYNC, HZ/10);

  	}

  	/* top priority shrink_zones still had more to do? don't OOM, then */

  	if (!sc->all_unreclaimable && scanning_global_lru(sc))

  		ret = sc->nr_reclaimed;

  out:

  	/*
  	 * Now that we've scanned all the zones at this priority level, note
  	 * that level within the zone so that the next thread which performs
  	 * scanning of this zone will immediately start out at this priority
  	 * level.  This affects only the decision whether or not to bring
  	 * mapped pages onto the inactive list.
  	 */
  	if (priority < 0)
  		priority = 0;

  	if (scanning_global_lru(sc)) {

  		for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {

  
  			if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
  				continue;
  
  			zone->prev_priority = priority;
  		}
  	} else
  		mem_cgroup_record_reclaim_priority(sc->mem_cgroup, priority);

  	delayacct_freepages_end();

  	return ret;
  }

  unsigned long try_to_free_pages(struct zonelist *zonelist, int order,

  				gfp_t gfp_mask, nodemask_t *nodemask)

  {
  	struct scan_control sc = {
  		.gfp_mask = gfp_mask,
  		.may_writepage = !laptop_mode,

  		.nr_to_reclaim = SWAP_CLUSTER_MAX,

  		.may_unmap = 1,

  		.may_swap = 1,

  		.swappiness = vm_swappiness,
  		.order = order,
  		.mem_cgroup = NULL,
  		.isolate_pages = isolate_pages_global,

  		.nodemask = nodemask,

  	};

  	return do_try_to_free_pages(zonelist, &sc);

  }

  #ifdef CONFIG_CGROUP_MEM_RES_CTLR

  unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
  						gfp_t gfp_mask, bool noswap,
  						unsigned int swappiness,
  						struct zone *zone, int nid)
  {
  	struct scan_control sc = {
  		.may_writepage = !laptop_mode,
  		.may_unmap = 1,
  		.may_swap = !noswap,

  		.swappiness = swappiness,
  		.order = 0,
  		.mem_cgroup = mem,
  		.isolate_pages = mem_cgroup_isolate_pages,
  	};
  	nodemask_t nm  = nodemask_of_node(nid);
  
  	sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
  			(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
  	sc.nodemask = &nm;
  	sc.nr_reclaimed = 0;
  	sc.nr_scanned = 0;
  	/*
  	 * NOTE: Although we can get the priority field, using it
  	 * here is not a good idea, since it limits the pages we can scan.
  	 * if we don't reclaim here, the shrink_zone from balance_pgdat
  	 * will pick up pages from other mem cgroup's as well. We hack
  	 * the priority and make it zero.
  	 */
  	shrink_zone(0, zone, &sc);
  	return sc.nr_reclaimed;
  }

  unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,

  					   gfp_t gfp_mask,
  					   bool noswap,
  					   unsigned int swappiness)

  {

  	struct zonelist *zonelist;

  	struct scan_control sc = {

  		.may_writepage = !laptop_mode,

  		.may_unmap = 1,

  		.may_swap = !noswap,

  		.nr_to_reclaim = SWAP_CLUSTER_MAX,

  		.swappiness = swappiness,

  		.order = 0,
  		.mem_cgroup = mem_cont,
  		.isolate_pages = mem_cgroup_isolate_pages,

  		.nodemask = NULL, /* we don't care the placement */

  	};

  	sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
  			(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
  	zonelist = NODE_DATA(numa_node_id())->node_zonelists;
  	return do_try_to_free_pages(zonelist, &sc);

  }
  #endif

  /* is kswapd sleeping prematurely? */

  static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)