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vmscan.c

/*
 *  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"

00051 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;

      /* 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;

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

      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_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\n",
                         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;
}

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

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

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

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

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

static inline int is_page_cache_freeable(struct page *page)
{
      return page_count(page) - !!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_write() against
       * this page's queue, we can perform writeback even if that
       * will block.
       *
       * If the page is swapcache, write it back even if that would
       * block, for some throttling. This happens by accident, because
       * swap_backing_dev_info is bust: it doesn't reflect the
       * congestion state of the swapdevs.  Easy to fix, if needed.
       * See swapfile.c:page_queue_congested().
       */
      if (!is_page_cache_freeable(page))
            return PAGE_KEEP;
      if (!mapping) {
            /*
             * Some data journaling orphaned pages can have
             * page->mapping == NULL while being dirty with clean buffers.
             */
            if (page_has_private(page)) {
                  if (try_to_free_buffers(page)) {
                        ClearPageDirty(page);
                        printk("%s: orphaned page\n", __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_is_file_cache(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);
      }

      /*
       * 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 */
}

/*
 * 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;
      unsigned long vm_flags;

      cond_resched();

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

            cond_resched();

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

            if (!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;
            }

            referenced = page_referenced(page, 1,
                                    sc->mem_cgroup, &vm_flags);
            /*
             * In active use or really unfreeable?  Activate it.
             * If page which have PG_mlocked lost isoltation race,
             * try_to_unmap moves it to unevictable list
             */
            if (sc->order <= PAGE_ALLOC_COSTLY_ORDER &&
                              referenced && page_mapping_inuse(page)
                              && !(vm_flags & VM_LOCKED))
                  goto activate_locked;

            /*
             * 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, 0)) {
                  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 (sc->order <= PAGE_ALLOC_COSTLY_ORDER && referenced)
                        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 (__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_is_file_cache(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;
}

/*
 * 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;

      /*
       * 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;

            nr_taken = sc->isolate_pages(sc->swap_cluster_max,
                       &page_list, &nr_scan, sc->order, mode,
                        zone, sc->mem_cgroup, 0, file);
            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]);

            if (scanning_global_lru(sc))
                  zone->pages_scanned += nr_scan;

            reclaim_stat->recent_scanned[0] += count[LRU_INACTIVE_ANON];
            reclaim_stat->recent_scanned[0] += count[LRU_ACTIVE_ANON];
            reclaim_stat->recent_scanned[1] += count[LRU_INACTIVE_FILE];
            reclaim_stat->recent_scanned[1] += count[LRU_ACTIVE_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_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scan);
                  __count_vm_events(KSWAPD_STEAL, nr_freed);
            } else if (scanning_global_lru(sc))
                  __count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scan);

            __count_zone_vm_events(PGSTEAL, zone, nr_freed);

            if (nr_taken == 0)
                  goto done;

            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 (PageActive(page)) {
                        int file = !!page_is_file_cache(page);
                        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);
                  }
            }
      } while (nr_scanned < max_scan);
      spin_unlock(&zone->lru_lock);
done:
      local_irq_enable();
      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);
            prefetchw_prev_lru_page(page, list, flags);

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

            VM_BUG_ON(!PageActive(page));
            if (!is_active_lru(lru))
                  ClearPageActive(page);  /* we are de-activating */

            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 pgmoved;
      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);

      lru_add_drain();
      spin_lock_irq(&zone->lru_lock);
      pgmoved = 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] += pgmoved;

      __count_zone_vm_events(PGREFILL, zone, pgscanned);
      if (file)
            __mod_zone_page_state(zone, NR_ACTIVE_FILE, -pgmoved);
      else
            __mod_zone_page_state(zone, NR_ACTIVE_ANON, -pgmoved);
      spin_unlock_irq(&zone->lru_lock);

      pgmoved = 0;  /* count referenced (mapping) mapped pages */
      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;
            }

            /* page_referenced clears PageReferenced */
            if (page_mapping_inuse(page) &&
                page_referenced(page, 0, sc->mem_cgroup, &vm_flags)) {
                  pgmoved++;
                  /*
                   * 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) && !PageAnon(page)) {
                        list_add(&page->lru, &l_active);
                        continue;
                  }
            }

            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] += pgmoved;

      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);

      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 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 (lru == LRU_ACTIVE_FILE && inactive_file_is_low(zone, sc)) {
            shrink_active_list(nr_to_scan, zone, sc, priority, file);
            return 0;
      }

      if (lru == LRU_ACTIVE_ANON && inactive_anon_is_low(zone, sc)) {
            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);

      anon  = zone_nr_pages(zone, sc, LRU_ACTIVE_ANON) +
            zone_nr_pages(zone, sc, LRU_INACTIVE_ANON);
      file  = zone_nr_pages(zone, sc, LRU_ACTIVE_FILE) +
            zone_nr_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 swap_cluster_max)
{
      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 swap_cluster_max = sc->swap_cluster_max;
      int noswap = 0;

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

      for_each_evictable_lru(l) {
            int file = is_file_lru(l);
            unsigned long scan;

            scan = zone_nr_pages(zone, sc, l);
            if (priority || noswap) {
                  scan >>= priority;
                  scan = (scan * percent[file]) / 100;
            }
            if (scanning_global_lru(sc))
                  nr[l] = nr_scan_try_batch(scan,
                                      &zone->lru[l].nr_saved_scan,
                                      swap_cluster_max);
            else
                  nr[l] = scan;
      }

      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(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 > swap_cluster_max &&
                  priority < DEF_PRIORITY && !current_is_kswapd())
                  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_is_all_unreclaimable(zone) &&
                                    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 pdflush and take explicit naps in the
 * hope that some of these pages can be written.  But if the allocating task
 * holds filesystem locks which prevent writeout this might not work, and the
 * allocation attempt will fail.
 *
 * 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);

      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_lru_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->swap_cluster_max) {
                  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.
             */
            if (total_scanned > sc->swap_cluster_max +
                              sc->swap_cluster_max / 2) {
                  wakeup_pdflush(laptop_mode ? 0 : total_scanned);
                  sc->may_writepage = 1;
            }

            /* Take a nap, wait for some writeback to complete */
            if (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,
            .swap_cluster_max = 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 try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
                                 gfp_t gfp_mask,
                                 bool noswap,
                                 unsigned int swappiness)
{
      struct scan_control sc = {
            .may_writepage = !laptop_mode,
            .may_unmap = 1,
            .may_swap = !noswap,
            .swap_cluster_max = 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 */
      };
      struct zonelist *zonelist;

      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

/*
 * For kswapd, balance_pgdat() will work across all this node's zones until
 * they are all at high_wmark_pages(zone).
 *
 * Returns the number of pages which were actually freed.
 *
 * There is special handling here for zones which are full of pinned pages.
 * This can happen if the pages are all mlocked, or if they are all used by
 * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
 * What we do is to detect the case where all pages in the zone have been
 * scanned twice and there has been zero successful reclaim.  Mark the zone as
 * dead and from now on, only perform a short scan.  Basically we're polling
 * the zone for when the problem goes away.
 *
 * kswapd scans the zones in the highmem->normal->dma direction.  It skips
 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
 * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
 * lower zones regardless of the number of free pages in the lower zones. This
 * interoperates with the page allocator fallback scheme to ensure that aging
 * of pages is balanced across the zones.
 */
static unsigned long balance_pgdat(pg_data_t *pgdat, int order)
{
      int all_zones_ok;
      int priority;
      int i;
      unsigned long total_scanned;
      struct reclaim_state *reclaim_state = current->reclaim_state;
      struct scan_control sc = {
            .gfp_mask = GFP_KERNEL,
            .may_unmap = 1,
            .may_swap = 1,
            .swap_cluster_max = SWAP_CLUSTER_MAX,
            .swappiness = vm_swappiness,
            .order = order,
            .mem_cgroup = NULL,
            .isolate_pages = isolate_pages_global,
      };
      /*
       * temp_priority is used to remember the scanning priority at which
       * this zone was successfully refilled to
       * free_pages == high_wmark_pages(zone).
       */
      int temp_priority[MAX_NR_ZONES];

loop_again:
      total_scanned = 0;
      sc.nr_reclaimed = 0;
      sc.may_writepage = !laptop_mode;
      count_vm_event(PAGEOUTRUN);

      for (i = 0; i < pgdat->nr_zones; i++)
            temp_priority[i] = DEF_PRIORITY;

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

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

            all_zones_ok = 1;

            /*
             * Scan in the highmem->dma direction for the highest
             * zone which needs scanning
             */
            for (i = pgdat->nr_zones - 1; i >= 0; i--) {
                  struct zone *zone = pgdat->node_zones + i;

                  if (!populated_zone(zone))
                        continue;

                  if (zone_is_all_unreclaimable(zone) &&
                      priority != DEF_PRIORITY)
                        continue;

                  /*
                   * Do some background aging of the anon list, to give
                   * pages a chance to be referenced before reclaiming.
                   */
                  if (inactive_anon_is_low(zone, &sc))
                        shrink_active_list(SWAP_CLUSTER_MAX, zone,
                                          &sc, priority, 0);

                  if (!zone_watermark_ok(zone, order,
                              high_wmark_pages(zone), 0, 0)) {
                        end_zone = i;
                        break;
                  }
            }
            if (i < 0)
                  goto out;

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

                  lru_pages += zone_lru_pages(zone);
            }

            /*
             * Now scan the zone in the dma->highmem direction, stopping
             * at the last zone which needs scanning.
             *
             * We do this because the page allocator works in the opposite
             * direction.  This prevents the page allocator from allocating
             * pages behind kswapd's direction of progress, which would
             * cause too much scanning of the lower zones.
             */
            for (i = 0; i <= end_zone; i++) {
                  struct zone *zone = pgdat->node_zones + i;
                  int nr_slab;

                  if (!populated_zone(zone))
                        continue;

                  if (zone_is_all_unreclaimable(zone) &&
                              priority != DEF_PRIORITY)
                        continue;

                  if (!zone_watermark_ok(zone, order,
                              high_wmark_pages(zone), end_zone, 0))
                        all_zones_ok = 0;
                  temp_priority[i] = priority;
                  sc.nr_scanned = 0;
                  note_zone_scanning_priority(zone, priority);
                  /*
                   * We put equal pressure on every zone, unless one
                   * zone has way too many pages free already.
                   */
                  if (!zone_watermark_ok(zone, order,
                              8*high_wmark_pages(zone), end_zone, 0))
                        shrink_zone(priority, zone, &sc);
                  reclaim_state->reclaimed_slab = 0;
                  nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
                                    lru_pages);
                  sc.nr_reclaimed += reclaim_state->reclaimed_slab;
                  total_scanned += sc.nr_scanned;
                  if (zone_is_all_unreclaimable(zone))
                        continue;
                  if (nr_slab == 0 && zone->pages_scanned >=
                                    (zone_lru_pages(zone) * 6))
                              zone_set_flag(zone,
                                          ZONE_ALL_UNRECLAIMABLE);
                  /*
                   * If we've done a decent amount of scanning and
                   * the reclaim ratio is low, start doing writepage
                   * even in laptop mode
                   */
                  if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
                      total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
                        sc.may_writepage = 1;
            }
            if (all_zones_ok)
                  break;            /* kswapd: all done */
            /*
             * OK, kswapd is getting into trouble.  Take a nap, then take
             * another pass across the zones.
             */
            if (total_scanned && priority < DEF_PRIORITY - 2)
                  congestion_wait(BLK_RW_ASYNC, HZ/10);

            /*
             * We do this so kswapd doesn't build up large priorities for
             * example when it is freeing in parallel with allocators. It
             * matches the direct reclaim path behaviour in terms of impact
             * on zone->*_priority.
             */
            if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
                  break;
      }
out:
      /*
       * Note within each zone the priority level at which this zone was
       * brought into a happy state.  So that the next thread which scans this
       * zone will start out at that priority level.
       */
      for (i = 0; i < pgdat->nr_zones; i++) {
            struct zone *zone = pgdat->node_zones + i;

            zone->prev_priority = temp_priority[i];
      }
      if (!all_zones_ok) {
            cond_resched();

            try_to_freeze();

            /*
             * Fragmentation may mean that the system cannot be
             * rebalanced for high-order allocations in all zones.
             * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX,
             * it means the zones have been fully scanned and are still
             * not balanced. For high-order allocations, there is
             * little point trying all over again as kswapd may
             * infinite loop.
             *
             * Instead, recheck all watermarks at order-0 as they
             * are the most important. If watermarks are ok, kswapd will go
             * back to sleep. High-order users can still perform direct
             * reclaim if they wish.
             */
            if (sc.nr_reclaimed < SWAP_CLUSTER_MAX)
                  order = sc.order = 0;

            goto loop_again;
      }

      return sc.nr_reclaimed;
}

/*
 * The background pageout daemon, started as a kernel thread
 * from the init process.
 *
 * This basically trickles out pages so that we have _some_
 * free memory available even if there is no other activity
 * that frees anything up. This is needed for things like routing
 * etc, where we otherwise might have all activity going on in
 * asynchronous contexts that cannot page things out.
 *
 * If there are applications that are active memory-allocators
 * (most normal use), this basically shouldn't matter.
 */
static int kswapd(void *p)
{
      unsigned long order;
      pg_data_t *pgdat = (pg_data_t*)p;
      struct task_struct *tsk = current;
      DEFINE_WAIT(wait);
      struct reclaim_state reclaim_state = {
            .reclaimed_slab = 0,
      };
      const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);

      lockdep_set_current_reclaim_state(GFP_KERNEL);

      if (!cpumask_empty(cpumask))
            set_cpus_allowed_ptr(tsk, cpumask);
      current->reclaim_state = &reclaim_state;

      /*
       * Tell the memory management that we're a "memory allocator",
       * and that if we need more memory we should get access to it
       * regardless (see "__alloc_pages()"). "kswapd" should
       * never get caught in the normal page freeing logic.
       *
       * (Kswapd normally doesn't need memory anyway, but sometimes
       * you need a small amount of memory in order to be able to
       * page out something else, and this flag essentially protects
       * us from recursively trying to free more memory as we're
       * trying to free the first piece of memory in the first place).
       */
      tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
      set_freezable();

      order = 0;
      for ( ; ; ) {
            unsigned long new_order;

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

                  order = pgdat->kswapd_max_order;
            }
            finish_wait(&pgdat->kswapd_wait, &wait);

            if (!try_to_freeze()) {
                  /* We can speed up thawing tasks if we don't call
                   * balance_pgdat after returning from the refrigerator
                   */
                  balance_pgdat(pgdat, order);
            }
      }
      return 0;
}

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

      if (!populated_zone(zone))
            return;

      pgdat = zone->zone_pgdat;
      if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0, 0))
            return;
      if (pgdat->kswapd_max_order < order)
            pgdat->kswapd_max_order = order;
      if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
            return;
      if (!waitqueue_active(&pgdat->kswapd_wait))
            return;
      wake_up_interruptible(&pgdat->kswapd_wait);
}

unsigned long global_lru_pages(void)
{
      return global_page_state(NR_ACTIVE_ANON)
            + global_page_state(NR_ACTIVE_FILE)
            + global_page_state(NR_INACTIVE_ANON)
            + global_page_state(NR_INACTIVE_FILE);
}

#ifdef CONFIG_HIBERNATION
/*
 * Helper function for shrink_all_memory().  Tries to reclaim 'nr_pages' pages
 * from LRU lists system-wide, for given pass and priority.
 *
 * For pass > 3 we also try to shrink the LRU lists that contain a few pages
 */
static void shrink_all_zones(unsigned long nr_pages, int prio,
                              int pass, struct scan_control *sc)
{
      struct zone *zone;
      unsigned long nr_reclaimed = 0;

      for_each_populated_zone(zone) {
            enum lru_list l;

            if (zone_is_all_unreclaimable(zone) && prio != DEF_PRIORITY)
                  continue;

            for_each_evictable_lru(l) {
                  enum zone_stat_item ls = NR_LRU_BASE + l;
                  unsigned long lru_pages = zone_page_state(zone, ls);

                  /* For pass = 0, we don't shrink the active list */
                  if (pass == 0 && (l == LRU_ACTIVE_ANON ||
                                    l == LRU_ACTIVE_FILE))
                        continue;

                  zone->lru[l].nr_saved_scan += (lru_pages >> prio) + 1;
                  if (zone->lru[l].nr_saved_scan >= nr_pages || pass > 3) {
                        unsigned long nr_to_scan;

                        zone->lru[l].nr_saved_scan = 0;
                        nr_to_scan = min(nr_pages, lru_pages);
                        nr_reclaimed += shrink_list(l, nr_to_scan, zone,
                                                sc, prio);
                        if (nr_reclaimed >= nr_pages) {
                              sc->nr_reclaimed += nr_reclaimed;
                              return;
                        }
                  }
            }
      }
      sc->nr_reclaimed += nr_reclaimed;
}

/*
 * Try to free `nr_pages' of memory, system-wide, and return the number of
 * freed pages.
 *
 * Rather than trying to age LRUs the aim is to preserve the overall
 * LRU order by reclaiming preferentially
 * inactive > active > active referenced > active mapped
 */
unsigned long shrink_all_memory(unsigned long nr_pages)
{
      unsigned long lru_pages, nr_slab;
      int pass;
      struct reclaim_state reclaim_state;
      struct scan_control sc = {
            .gfp_mask = GFP_KERNEL,
            .may_unmap = 0,
            .may_writepage = 1,
            .isolate_pages = isolate_pages_global,
            .nr_reclaimed = 0,
      };

      current->reclaim_state = &reclaim_state;

      lru_pages = global_lru_pages();
      nr_slab = global_page_state(NR_SLAB_RECLAIMABLE);
      /* If slab caches are huge, it's better to hit them first */
      while (nr_slab >= lru_pages) {
            reclaim_state.reclaimed_slab = 0;
            shrink_slab(nr_pages, sc.gfp_mask, lru_pages);
            if (!reclaim_state.reclaimed_slab)
                  break;

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

            nr_slab -= reclaim_state.reclaimed_slab;
      }

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

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

            for (prio = DEF_PRIORITY; prio >= 0; prio--) {
                  unsigned long nr_to_scan = nr_pages - sc.nr_reclaimed;

                  sc.nr_scanned = 0;
                  sc.swap_cluster_max = nr_to_scan;
                  shrink_all_zones(nr_to_scan, prio, pass, &sc);
                  if (sc.nr_reclaimed >= nr_pages)
                        goto out;

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

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

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


out:
      current->reclaim_state = NULL;

      return sc.nr_reclaimed;
}
#endif /* CONFIG_HIBERNATION */

/* It's optimal to keep kswapds on the same CPUs as their memory, but
   not required for correctness.  So if the last cpu in a node goes
   away, we get changed to run anywhere: as the first one comes back,
   restore their cpu bindings. */
static int __devinit cpu_callback(struct notifier_block *nfb,
                          unsigned long action, void *hcpu)
{
      int nid;

      if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
            for_each_node_state(nid, N_HIGH_MEMORY) {
                  pg_data_t *pgdat = NODE_DATA(nid);
                  const struct cpumask *mask;

                  mask = cpumask_of_node(pgdat->node_id);

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

/*
 * This kswapd start function will be called by init and node-hot-add.
 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
 */
int kswapd_run(int nid)
{
      pg_data_t *pgdat = NODE_DATA(nid);
      int ret = 0;

      if (pgdat->kswapd)
            return 0;

      pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
      if (IS_ERR(pgdat->kswapd)) {
            /* failure at boot is fatal */
            BUG_ON(system_state == SYSTEM_BOOTING);
            printk("Failed to start kswapd on node %d\n",nid);
            ret = -1;
      }
      return ret;
}

static int __init kswapd_init(void)
{
      int nid;

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

module_init(kswapd_init)

#ifdef CONFIG_NUMA
/*
 * Zone reclaim mode
 *
 * If non-zero call zone_reclaim when the number of free pages falls below
 * the watermarks.
 */
int zone_reclaim_mode __read_mostly;

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

/*
 * Priority for ZONE_RECLAIM. This determines the fraction of pages
 * of a node considered for each zone_reclaim. 4 scans 1/16th of
 * a zone.
 */
#define ZONE_RECLAIM_PRIORITY 4

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

/*
 * If the number of slab pages in a zone grows beyond this percentage then
 * slab reclaim needs to occur.
 */
int sysctl_min_slab_ratio = 5;

static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
{
      unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
      unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
            zone_page_state(zone, NR_ACTIVE_FILE);

      /*
       * It's possible for there to be more file mapped pages than
       * accounted for by the pages on the file LRU lists because
       * tmpfs pages accounted for as ANON can also be FILE_MAPPED
       */
      return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
}

/* Work out how many page cache pages we can reclaim in this reclaim_mode */
static long zone_pagecache_reclaimable(struct zone *zone)
{
      long nr_pagecache_reclaimable;
      long delta = 0;

      /*
       * If RECLAIM_SWAP is set, then all file pages are considered
       * potentially reclaimable. Otherwise, we have to worry about
       * pages like swapcache and zone_unmapped_file_pages() provides
       * a better estimate
       */
      if (zone_reclaim_mode & RECLAIM_SWAP)
            nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
      else
            nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);

      /* If we can't clean pages, remove dirty pages from consideration */
      if (!(zone_reclaim_mode & RECLAIM_WRITE))
            delta += zone_page_state(zone, NR_FILE_DIRTY);

      /* Watch for any possible underflows due to delta */
      if (unlikely(delta > nr_pagecache_reclaimable))
            delta = nr_pagecache_reclaimable;

      return nr_pagecache_reclaimable - delta;
}

/*
 * Try to free up some pages from this zone through reclaim.
 */
static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
{
      /* Minimum pages needed in order to stay on node */
      const unsigned long nr_pages = 1 << order;
      struct task_struct *p = current;
      struct reclaim_state reclaim_state;
      int priority;
      struct scan_control sc = {
            .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
            .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
            .may_swap = 1,
            .swap_cluster_max = max_t(unsigned long, nr_pages,
                              SWAP_CLUSTER_MAX),
            .gfp_mask = gfp_mask,
            .swappiness = vm_swappiness,
            .order = order,
            .isolate_pages = isolate_pages_global,
      };
      unsigned long slab_reclaimable;

      disable_swap_token();
      cond_resched();
      /*
       * We need to be able to allocate from the reserves for RECLAIM_SWAP
       * and we also need to be able to write out pages for RECLAIM_WRITE
       * and RECLAIM_SWAP.
       */
      p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
      reclaim_state.reclaimed_slab = 0;
      p->reclaim_state = &reclaim_state;

      if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
            /*
             * Free memory by calling shrink zone with increasing
             * priorities until we have enough memory freed.
             */
            priority = ZONE_RECLAIM_PRIORITY;
            do {
                  note_zone_scanning_priority(zone, priority);
                  shrink_zone(priority, zone, &sc);
                  priority--;
            } while (priority >= 0 && sc.nr_reclaimed < nr_pages);
      }

      slab_reclaimable = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
      if (slab_reclaimable > zone->min_slab_pages) {
            /*
             * shrink_slab() does not currently allow us to determine how
             * many pages were freed in this zone. So we take the current
             * number of slab pages and shake the slab until it is reduced
             * by the same nr_pages that we used for reclaiming unmapped
             * pages.
             *
             * Note that shrink_slab will free memory on all zones and may
             * take a long time.
             */
            while (shrink_slab(sc.nr_scanned, gfp_mask, order) &&
                  zone_page_state(zone, NR_SLAB_RECLAIMABLE) >
                        slab_reclaimable - nr_pages)
                  ;

            /*
             * Update nr_reclaimed by the number of slab pages we
             * reclaimed from this zone.
             */
            sc.nr_reclaimed += slab_reclaimable -
                  zone_page_state(zone, NR_SLAB_RECLAIMABLE);
      }

      p->reclaim_state = NULL;
      current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
      return sc.nr_reclaimed >= nr_pages;
}

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

      /*
       * Zone reclaim reclaims unmapped file backed pages and
       * slab pages if we are over the defined limits.
       *
       * A small portion of unmapped file backed pages is needed for
       * file I/O otherwise pages read by file I/O will be immediately
       * thrown out if the zone is overallocated. So we do not reclaim
       * if less than a specified percentage of the zone is used by
       * unmapped file backed pages.
       */
      if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
          zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
            return ZONE_RECLAIM_FULL;

      if (zone_is_all_unreclaimable(zone))
            return ZONE_RECLAIM_FULL;

      /*
       * Do not scan if the allocation should not be delayed.
       */
      if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
            return ZONE_RECLAIM_NOSCAN;

      /*
       * Only run zone reclaim on the local zone or on zones that do not
       * have associated processors. This will favor the local processor
       * over remote processors and spread off node memory allocations
       * as wide as possible.
       */
      node_id = zone_to_nid(zone);
      if (node_state(node_id, N_CPU) && node_id != numa_node_id())
            return ZONE_RECLAIM_NOSCAN;

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

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

      if (!ret)
            count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);

      return ret;
}
#endif

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

      if (mapping_unevictable(page_mapping(page)))
            return 0;

      if (PageMlocked(page) || (vma && is_mlocked_vma(vma, page)))
            return 0;

      return 1;
}

/**
 * check_move_unevictable_page - check page for evictability and move to appropriate zone lru list
 * @page: page to check evictability and move to appropriate lru list
 * @zone: zone page is in
 *
 * Checks a page for evictability and moves the page to the appropriate
 * zone lru list.
 *
 * Restrictions: zone->lru_lock must be held, page must be on LRU and must
 * have PageUnevictable set.
 */
static void check_move_unevictable_page(struct page *page, struct zone *zone)
{
      VM_BUG_ON(PageActive(page));

retry:
      ClearPageUnevictable(page);
      if (page_evictable(page, NULL)) {
            enum lru_list l = LRU_INACTIVE_ANON + page_is_file_cache(page);

            __dec_zone_state(zone, NR_UNEVICTABLE);
            list_move(&page->lru, &zone->lru[l].list);
            mem_cgroup_move_lists(page, LRU_UNEVICTABLE, l);
            __inc_zone_state(zone, NR_INACTIVE_ANON + l);
            __count_vm_event(UNEVICTABLE_PGRESCUED);
      } else {
            /*
             * rotate unevictable list
             */
            SetPageUnevictable(page);
            list_move(&page->lru, &zone->lru[LRU_UNEVICTABLE].list);
            mem_cgroup_rotate_lru_list(page, LRU_UNEVICTABLE);
            if (page_evictable(page, NULL))
                  goto retry;
      }
}

/**
 * scan_mapping_unevictable_pages - scan an address space for evictable pages
 * @mapping: struct address_space to scan for evictable pages
 *
 * Scan all pages in mapping.  Check unevictable pages for
 * evictability and move them to the appropriate zone lru list.
 */
void scan_mapping_unevictable_pages(struct address_space *mapping)
{
      pgoff_t next = 0;
      pgoff_t end   = (i_size_read(mapping->host) + PAGE_CACHE_SIZE - 1) >>
                   PAGE_CACHE_SHIFT;
      struct zone *zone;
      struct pagevec pvec;

      if (mapping->nrpages == 0)
            return;

      pagevec_init(&pvec, 0);
      while (next < end &&
            pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
            int i;
            int pg_scanned = 0;

            zone = NULL;

            for (i = 0; i < pagevec_count(&pvec); i++) {
                  struct page *page = pvec.pages[i];
                  pgoff_t page_index = page->index;
                  struct zone *pagezone = page_zone(page);

                  pg_scanned++;
                  if (page_index > next)
                        next = page_index;
                  next++;

                  if (pagezone != zone) {
                        if (zone)
                              spin_unlock_irq(&zone->lru_lock);
                        zone = pagezone;
                        spin_lock_irq(&zone->lru_lock);
                  }

                  if (PageLRU(page) && PageUnevictable(page))
                        check_move_unevictable_page(page, zone);
            }
            if (zone)
                  spin_unlock_irq(&zone->lru_lock);
            pagevec_release(&pvec);

            count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned);
      }

}

/**
 * scan_zone_unevictable_pages - check unevictable list for evictable pages
 * @zone - zone of which to scan the unevictable list
 *
 * Scan @zone's unevictable LRU lists to check for pages that have become
 * evictable.  Move those that have to @zone's inactive list where they
 * become candidates for reclaim, unless shrink_inactive_zone() decides
 * to reactivate them.  Pages that are still unevictable are rotated
 * back onto @zone's unevictable list.
 */
#define SCAN_UNEVICTABLE_BATCH_SIZE 16UL /* arbitrary lock hold batch size */
static void scan_zone_unevictable_pages(struct zone *zone)
{
      struct list_head *l_unevictable = &zone->lru[LRU_UNEVICTABLE].list;
      unsigned long scan;
      unsigned long nr_to_scan = zone_page_state(zone, NR_UNEVICTABLE);

      while (nr_to_scan > 0) {
            unsigned long batch_size = min(nr_to_scan,
                                    SCAN_UNEVICTABLE_BATCH_SIZE);

            spin_lock_irq(&zone->lru_lock);
            for (scan = 0;  scan < batch_size; scan++) {
                  struct page *page = lru_to_page(l_unevictable);

                  if (!trylock_page(page))
                        continue;

                  prefetchw_prev_lru_page(page, l_unevictable, flags);

                  if (likely(PageLRU(page) && PageUnevictable(page)))
                        check_move_unevictable_page(page, zone);

                  unlock_page(page);
            }
            spin_unlock_irq(&zone->lru_lock);

            nr_to_scan -= batch_size;
      }
}


/**
 * scan_all_zones_unevictable_pages - scan all unevictable lists for evictable pages
 *
 * A really big hammer:  scan all zones' unevictable LRU lists to check for
 * pages that have become evictable.  Move those back to the zones'
 * inactive list where they become candidates for reclaim.
 * This occurs when, e.g., we have unswappable pages on the unevictable lists,
 * and we add swap to the system.  As such, it runs in the context of a task
 * that has possibly/probably made some previously unevictable pages
 * evictable.
 */
static void scan_all_zones_unevictable_pages(void)
{
      struct zone *zone;

      for_each_zone(zone) {
            scan_zone_unevictable_pages(zone);
      }
}

/*
 * scan_unevictable_pages [vm] sysctl handler.  On demand re-scan of
 * all nodes' unevictable lists for evictable pages
 */
unsigned long scan_unevictable_pages;

int scan_unevictable_handler(struct ctl_table *table, int write,
                     struct file *file, void __user *buffer,
                     size_t *length, loff_t *ppos)
{
      proc_doulongvec_minmax(table, write, file, buffer, length, ppos);

      if (write && *(unsigned long *)table->data)
            scan_all_zones_unevictable_pages();

      scan_unevictable_pages = 0;
      return 0;
}

/*
 * per node 'scan_unevictable_pages' attribute.  On demand re-scan of
 * a specified node's per zone unevictable lists for evictable pages.
 */

static ssize_t read_scan_unevictable_node(struct sys_device *dev,
                                struct sysdev_attribute *attr,
                                char *buf)
{
      return sprintf(buf, "0\n");   /* always zero; should fit... */
}

static ssize_t write_scan_unevictable_node(struct sys_device *dev,
                                 struct sysdev_attribute *attr,
                              const char *buf, size_t count)
{
      struct zone *node_zones = NODE_DATA(dev->id)->node_zones;
      struct zone *zone;
      unsigned long res;
      unsigned long req = strict_strtoul(buf, 10, &res);

      if (!req)
            return 1;   /* zero is no-op */

      for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) {
            if (!populated_zone(zone))
                  continue;
            scan_zone_unevictable_pages(zone);
      }
      return 1;
}


static SYSDEV_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
                  read_scan_unevictable_node,
                  write_scan_unevictable_node);

int scan_unevictable_register_node(struct node *node)
{
      return sysdev_create_file(&node->sysdev, &attr_scan_unevictable_pages);
}

void scan_unevictable_unregister_node(struct node *node)
{
      sysdev_remove_file(&node->sysdev, &attr_scan_unevictable_pages);
}


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