/*
   *  linux/mm/swap.c
   *
   *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
   */
  
  /*

   * This file contains the default values for the operation of the

   * Linux VM subsystem. Fine-tuning documentation can be found in
   * Documentation/sysctl/vm.txt.
   * Started 18.12.91
   * Swap aging added 23.2.95, Stephen Tweedie.
   * Buffermem limits added 12.3.98, Rik van Riel.
   */
  
  #include <linux/mm.h>
  #include <linux/sched.h>
  #include <linux/kernel_stat.h>
  #include <linux/swap.h>
  #include <linux/mman.h>
  #include <linux/pagemap.h>
  #include <linux/pagevec.h>
  #include <linux/init.h>

  #include <linux/export.h>

  #include <linux/mm_inline.h>

  #include <linux/percpu_counter.h>

  #include <linux/memremap.h>

  #include <linux/percpu.h>
  #include <linux/cpu.h>
  #include <linux/notifier.h>

  #include <linux/backing-dev.h>

  #include <linux/memcontrol.h>

  #include <linux/gfp.h>

  #include <linux/uio.h>

  #include <linux/hugetlb.h>

  #include <linux/page_idle.h>

  #include "internal.h"

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

  /* How many pages do we try to swap or page in/out together? */
  int page_cluster;

  static DEFINE_PER_CPU(struct pagevec, lru_add_pvec);

  static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);

  static DEFINE_PER_CPU(struct pagevec, lru_deactivate_file_pvecs);

  static DEFINE_PER_CPU(struct pagevec, lru_lazyfree_pvecs);

  #ifdef CONFIG_SMP
  static DEFINE_PER_CPU(struct pagevec, activate_page_pvecs);
  #endif

  /*
   * This path almost never happens for VM activity - pages are normally
   * freed via pagevecs.  But it gets used by networking.
   */

  static void __page_cache_release(struct page *page)

  {
  	if (PageLRU(page)) {

  		struct zone *zone = page_zone(page);

  		struct lruvec *lruvec;
  		unsigned long flags;

  		spin_lock_irqsave(zone_lru_lock(zone), flags);

  		lruvec = mem_cgroup_page_lruvec(page, zone->zone_pgdat);

  		VM_BUG_ON_PAGE(!PageLRU(page), page);

  		__ClearPageLRU(page);

  		del_page_from_lru_list(page, lruvec, page_off_lru(page));

  		spin_unlock_irqrestore(zone_lru_lock(zone), flags);

  	}

  	__ClearPageWaiters(page);

  	mem_cgroup_uncharge(page);

  }
  
  static void __put_single_page(struct page *page)
  {
  	__page_cache_release(page);

  	free_hot_cold_page(page, false);

  }

  static void __put_compound_page(struct page *page)

  {

  	compound_page_dtor *dtor;

  	/*
  	 * __page_cache_release() is supposed to be called for thp, not for
  	 * hugetlb. This is because hugetlb page does never have PageLRU set
  	 * (it's never listed to any LRU lists) and no memcg routines should
  	 * be called for hugetlb (it has a separate hugetlb_cgroup.)
  	 */
  	if (!PageHuge(page))
  		__page_cache_release(page);

  	dtor = get_compound_page_dtor(page);
  	(*dtor)(page);
  }

  void __put_page(struct page *page)

  {

  	if (is_zone_device_page(page)) {
  		put_dev_pagemap(page->pgmap);
  
  		/*
  		 * The page belongs to the device that created pgmap. Do
  		 * not return it to page allocator.
  		 */
  		return;
  	}

  	if (unlikely(PageCompound(page)))

  		__put_compound_page(page);
  	else

  		__put_single_page(page);

  }

  EXPORT_SYMBOL(__put_page);

  /**

   * put_pages_list() - release a list of pages
   * @pages: list of pages threaded on page->lru

   *
   * Release a list of pages which are strung together on page.lru.  Currently
   * used by read_cache_pages() and related error recovery code.

   */
  void put_pages_list(struct list_head *pages)
  {
  	while (!list_empty(pages)) {
  		struct page *victim;
  
  		victim = list_entry(pages->prev, struct page, lru);
  		list_del(&victim->lru);

  		put_page(victim);

  	}
  }
  EXPORT_SYMBOL(put_pages_list);

  /*
   * get_kernel_pages() - pin kernel pages in memory
   * @kiov:	An array of struct kvec structures
   * @nr_segs:	number of segments to pin
   * @write:	pinning for read/write, currently ignored
   * @pages:	array that receives pointers to the pages pinned.
   *		Should be at least nr_segs long.
   *
   * Returns number of pages pinned. This may be fewer than the number
   * requested. If nr_pages is 0 or negative, returns 0. If no pages
   * were pinned, returns -errno. Each page returned must be released
   * with a put_page() call when it is finished with.
   */
  int get_kernel_pages(const struct kvec *kiov, int nr_segs, int write,
  		struct page **pages)
  {
  	int seg;
  
  	for (seg = 0; seg < nr_segs; seg++) {
  		if (WARN_ON(kiov[seg].iov_len != PAGE_SIZE))
  			return seg;

  		pages[seg] = kmap_to_page(kiov[seg].iov_base);

  		get_page(pages[seg]);

  	}
  
  	return seg;
  }
  EXPORT_SYMBOL_GPL(get_kernel_pages);
  
  /*
   * get_kernel_page() - pin a kernel page in memory
   * @start:	starting kernel address
   * @write:	pinning for read/write, currently ignored
   * @pages:	array that receives pointer to the page pinned.
   *		Must be at least nr_segs long.
   *
   * Returns 1 if page is pinned. If the page was not pinned, returns
   * -errno. The page returned must be released with a put_page() call
   * when it is finished with.
   */
  int get_kernel_page(unsigned long start, int write, struct page **pages)
  {
  	const struct kvec kiov = {
  		.iov_base = (void *)start,
  		.iov_len = PAGE_SIZE
  	};
  
  	return get_kernel_pages(&kiov, 1, write, pages);
  }
  EXPORT_SYMBOL_GPL(get_kernel_page);

  static void pagevec_lru_move_fn(struct pagevec *pvec,

  	void (*move_fn)(struct page *page, struct lruvec *lruvec, void *arg),
  	void *arg)

  {
  	int i;

  	struct pglist_data *pgdat = NULL;

  	struct lruvec *lruvec;

  	unsigned long flags = 0;

  
  	for (i = 0; i < pagevec_count(pvec); i++) {
  		struct page *page = pvec->pages[i];

  		struct pglist_data *pagepgdat = page_pgdat(page);

  		if (pagepgdat != pgdat) {
  			if (pgdat)
  				spin_unlock_irqrestore(&pgdat->lru_lock, flags);
  			pgdat = pagepgdat;
  			spin_lock_irqsave(&pgdat->lru_lock, flags);

  		}

  		lruvec = mem_cgroup_page_lruvec(page, pgdat);

  		(*move_fn)(page, lruvec, arg);

  	}

  	if (pgdat)
  		spin_unlock_irqrestore(&pgdat->lru_lock, flags);

  	release_pages(pvec->pages, pvec->nr, pvec->cold);
  	pagevec_reinit(pvec);

  }

  static void pagevec_move_tail_fn(struct page *page, struct lruvec *lruvec,
  				 void *arg)

  {
  	int *pgmoved = arg;

  	if (PageLRU(page) && !PageUnevictable(page)) {
  		del_page_from_lru_list(page, lruvec, page_lru(page));
  		ClearPageActive(page);
  		add_page_to_lru_list_tail(page, lruvec, page_lru(page));

  		(*pgmoved)++;
  	}
  }
  
  /*
   * pagevec_move_tail() must be called with IRQ disabled.
   * Otherwise this may cause nasty races.
   */
  static void pagevec_move_tail(struct pagevec *pvec)
  {
  	int pgmoved = 0;
  
  	pagevec_lru_move_fn(pvec, pagevec_move_tail_fn, &pgmoved);
  	__count_vm_events(PGROTATED, pgmoved);
  }

  /*

   * Writeback is about to end against a page which has been marked for immediate
   * reclaim.  If it still appears to be reclaimable, move it to the tail of the

   * inactive list.

   */

  void rotate_reclaimable_page(struct page *page)

  {

  	if (!PageLocked(page) && !PageDirty(page) &&

  	    !PageUnevictable(page) && PageLRU(page)) {

  		struct pagevec *pvec;
  		unsigned long flags;

  		get_page(page);

  		local_irq_save(flags);

  		pvec = this_cpu_ptr(&lru_rotate_pvecs);

  		if (!pagevec_add(pvec, page) || PageCompound(page))

  			pagevec_move_tail(pvec);
  		local_irq_restore(flags);
  	}

  }

  static void update_page_reclaim_stat(struct lruvec *lruvec,

  				     int file, int rotated)
  {

  	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;

  
  	reclaim_stat->recent_scanned[file]++;
  	if (rotated)
  		reclaim_stat->recent_rotated[file]++;

  }

  static void __activate_page(struct page *page, struct lruvec *lruvec,
  			    void *arg)

  {

  	if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {

  		int file = page_is_file_cache(page);
  		int lru = page_lru_base_type(page);

  		del_page_from_lru_list(page, lruvec, lru);

  		SetPageActive(page);
  		lru += LRU_ACTIVE;

  		add_page_to_lru_list(page, lruvec, lru);

  		trace_mm_lru_activate(page);

  		__count_vm_event(PGACTIVATE);
  		update_page_reclaim_stat(lruvec, file, 1);

  	}

  }
  
  #ifdef CONFIG_SMP

  static void activate_page_drain(int cpu)
  {
  	struct pagevec *pvec = &per_cpu(activate_page_pvecs, cpu);
  
  	if (pagevec_count(pvec))
  		pagevec_lru_move_fn(pvec, __activate_page, NULL);
  }

  static bool need_activate_page_drain(int cpu)
  {
  	return pagevec_count(&per_cpu(activate_page_pvecs, cpu)) != 0;
  }

  void activate_page(struct page *page)
  {

  	page = compound_head(page);

  	if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
  		struct pagevec *pvec = &get_cpu_var(activate_page_pvecs);

  		get_page(page);

  		if (!pagevec_add(pvec, page) || PageCompound(page))

  			pagevec_lru_move_fn(pvec, __activate_page, NULL);
  		put_cpu_var(activate_page_pvecs);
  	}
  }
  
  #else
  static inline void activate_page_drain(int cpu)
  {
  }

  static bool need_activate_page_drain(int cpu)
  {
  	return false;
  }

  void activate_page(struct page *page)
  {
  	struct zone *zone = page_zone(page);

  	page = compound_head(page);

  	spin_lock_irq(zone_lru_lock(zone));

  	__activate_page(page, mem_cgroup_page_lruvec(page, zone->zone_pgdat), NULL);

  	spin_unlock_irq(zone_lru_lock(zone));

  }

  #endif

  static void __lru_cache_activate_page(struct page *page)
  {
  	struct pagevec *pvec = &get_cpu_var(lru_add_pvec);
  	int i;
  
  	/*
  	 * Search backwards on the optimistic assumption that the page being
  	 * activated has just been added to this pagevec. Note that only
  	 * the local pagevec is examined as a !PageLRU page could be in the
  	 * process of being released, reclaimed, migrated or on a remote
  	 * pagevec that is currently being drained. Furthermore, marking
  	 * a remote pagevec's page PageActive potentially hits a race where
  	 * a page is marked PageActive just after it is added to the inactive
  	 * list causing accounting errors and BUG_ON checks to trigger.
  	 */
  	for (i = pagevec_count(pvec) - 1; i >= 0; i--) {
  		struct page *pagevec_page = pvec->pages[i];
  
  		if (pagevec_page == page) {
  			SetPageActive(page);
  			break;
  		}
  	}
  
  	put_cpu_var(lru_add_pvec);
  }

  /*
   * Mark a page as having seen activity.
   *
   * inactive,unreferenced	->	inactive,referenced
   * inactive,referenced		->	active,unreferenced
   * active,unreferenced		->	active,referenced

   *
   * When a newly allocated page is not yet visible, so safe for non-atomic ops,
   * __SetPageReferenced(page) may be substituted for mark_page_accessed(page).

   */

  void mark_page_accessed(struct page *page)

  {

  	page = compound_head(page);

  	if (!PageActive(page) && !PageUnevictable(page) &&

  			PageReferenced(page)) {
  
  		/*
  		 * If the page is on the LRU, queue it for activation via
  		 * activate_page_pvecs. Otherwise, assume the page is on a
  		 * pagevec, mark it active and it'll be moved to the active
  		 * LRU on the next drain.
  		 */
  		if (PageLRU(page))
  			activate_page(page);
  		else
  			__lru_cache_activate_page(page);

  		ClearPageReferenced(page);

  		if (page_is_file_cache(page))
  			workingset_activation(page);

  	} else if (!PageReferenced(page)) {
  		SetPageReferenced(page);
  	}

  	if (page_is_idle(page))
  		clear_page_idle(page);

  }

  EXPORT_SYMBOL(mark_page_accessed);

  static void __lru_cache_add(struct page *page)

  {

  	struct pagevec *pvec = &get_cpu_var(lru_add_pvec);

  	get_page(page);

  	if (!pagevec_add(pvec, page) || PageCompound(page))

  		__pagevec_lru_add(pvec);

  	put_cpu_var(lru_add_pvec);

  }

  
  /**
   * lru_cache_add: add a page to the page lists
   * @page: the page to add
   */
  void lru_cache_add_anon(struct page *page)
  {

  	if (PageActive(page))
  		ClearPageActive(page);

  	__lru_cache_add(page);
  }
  
  void lru_cache_add_file(struct page *page)
  {

  	if (PageActive(page))
  		ClearPageActive(page);

  	__lru_cache_add(page);
  }
  EXPORT_SYMBOL(lru_cache_add_file);

  /**

   * lru_cache_add - add a page to a page list

   * @page: the page to be added to the LRU.

   *
   * Queue the page for addition to the LRU via pagevec. The decision on whether
   * to add the page to the [in]active [file|anon] list is deferred until the
   * pagevec is drained. This gives a chance for the caller of lru_cache_add()
   * have the page added to the active list using mark_page_accessed().

   */

  void lru_cache_add(struct page *page)

  {

  	VM_BUG_ON_PAGE(PageActive(page) && PageUnevictable(page), page);
  	VM_BUG_ON_PAGE(PageLRU(page), page);

  	__lru_cache_add(page);

  }

  /**
   * add_page_to_unevictable_list - add a page to the unevictable list
   * @page:  the page to be added to the unevictable list
   *
   * Add page directly to its zone's unevictable list.  To avoid races with
   * tasks that might be making the page evictable, through eg. munlock,
   * munmap or exit, while it's not on the lru, we want to add the page
   * while it's locked or otherwise "invisible" to other tasks.  This is
   * difficult to do when using the pagevec cache, so bypass that.
   */
  void add_page_to_unevictable_list(struct page *page)
  {

  	struct pglist_data *pgdat = page_pgdat(page);

  	struct lruvec *lruvec;

  	spin_lock_irq(&pgdat->lru_lock);
  	lruvec = mem_cgroup_page_lruvec(page, pgdat);

  	ClearPageActive(page);

  	SetPageUnevictable(page);
  	SetPageLRU(page);

  	add_page_to_lru_list(page, lruvec, LRU_UNEVICTABLE);

  	spin_unlock_irq(&pgdat->lru_lock);

  }

  /**
   * lru_cache_add_active_or_unevictable
   * @page:  the page to be added to LRU
   * @vma:   vma in which page is mapped for determining reclaimability
   *
   * Place @page on the active or unevictable LRU list, depending on its
   * evictability.  Note that if the page is not evictable, it goes
   * directly back onto it's zone's unevictable list, it does NOT use a
   * per cpu pagevec.
   */
  void lru_cache_add_active_or_unevictable(struct page *page,
  					 struct vm_area_struct *vma)
  {
  	VM_BUG_ON_PAGE(PageLRU(page), page);
  
  	if (likely((vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) != VM_LOCKED)) {
  		SetPageActive(page);
  		lru_cache_add(page);
  		return;
  	}
  
  	if (!TestSetPageMlocked(page)) {
  		/*
  		 * We use the irq-unsafe __mod_zone_page_stat because this
  		 * counter is not modified from interrupt context, and the pte
  		 * lock is held(spinlock), which implies preemption disabled.
  		 */
  		__mod_zone_page_state(page_zone(page), NR_MLOCK,
  				    hpage_nr_pages(page));
  		count_vm_event(UNEVICTABLE_PGMLOCKED);
  	}
  	add_page_to_unevictable_list(page);
  }

  /*

   * If the page can not be invalidated, it is moved to the
   * inactive list to speed up its reclaim.  It is moved to the
   * head of the list, rather than the tail, to give the flusher
   * threads some time to write it out, as this is much more
   * effective than the single-page writeout from reclaim.

   *
   * If the page isn't page_mapped and dirty/writeback, the page
   * could reclaim asap using PG_reclaim.
   *
   * 1. active, mapped page -> none
   * 2. active, dirty/writeback page -> inactive, head, PG_reclaim
   * 3. inactive, mapped page -> none
   * 4. inactive, dirty/writeback page -> inactive, head, PG_reclaim
   * 5. inactive, clean -> inactive, tail
   * 6. Others -> none
   *
   * In 4, why it moves inactive's head, the VM expects the page would
   * be write it out by flusher threads as this is much more effective
   * than the single-page writeout from reclaim.

   */

  static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec,

  			      void *arg)

  {
  	int lru, file;

  	bool active;

  	if (!PageLRU(page))

  		return;

  	if (PageUnevictable(page))
  		return;

  	/* Some processes are using the page */
  	if (page_mapped(page))
  		return;

  	active = PageActive(page);

  	file = page_is_file_cache(page);
  	lru = page_lru_base_type(page);

  
  	del_page_from_lru_list(page, lruvec, lru + active);

  	ClearPageActive(page);
  	ClearPageReferenced(page);

  	add_page_to_lru_list(page, lruvec, lru);

  	if (PageWriteback(page) || PageDirty(page)) {
  		/*
  		 * PG_reclaim could be raced with end_page_writeback
  		 * It can make readahead confusing.  But race window
  		 * is _really_ small and  it's non-critical problem.
  		 */
  		SetPageReclaim(page);
  	} else {
  		/*
  		 * The page's writeback ends up during pagevec
  		 * We moves tha page into tail of inactive.
  		 */

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

  		__count_vm_event(PGROTATED);
  	}
  
  	if (active)
  		__count_vm_event(PGDEACTIVATE);

  	update_page_reclaim_stat(lruvec, file, 0);

  }

  static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec,

  			    void *arg)
  {

  	if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) &&

  	    !PageSwapCache(page) && !PageUnevictable(page)) {

  		bool active = PageActive(page);

  		del_page_from_lru_list(page, lruvec,
  				       LRU_INACTIVE_ANON + active);

  		ClearPageActive(page);
  		ClearPageReferenced(page);

  		/*
  		 * lazyfree pages are clean anonymous pages. They have
  		 * SwapBacked flag cleared to distinguish normal anonymous
  		 * pages
  		 */
  		ClearPageSwapBacked(page);
  		add_page_to_lru_list(page, lruvec, LRU_INACTIVE_FILE);

  		__count_vm_events(PGLAZYFREE, hpage_nr_pages(page));

  		count_memcg_page_event(page, PGLAZYFREE);

  		update_page_reclaim_stat(lruvec, 1, 0);

  	}
  }

  /*

   * Drain pages out of the cpu's pagevecs.
   * Either "cpu" is the current CPU, and preemption has already been
   * disabled; or "cpu" is being hot-unplugged, and is already dead.
   */

  void lru_add_drain_cpu(int cpu)

  {

  	struct pagevec *pvec = &per_cpu(lru_add_pvec, cpu);

  	if (pagevec_count(pvec))

  		__pagevec_lru_add(pvec);

  
  	pvec = &per_cpu(lru_rotate_pvecs, cpu);
  	if (pagevec_count(pvec)) {
  		unsigned long flags;
  
  		/* No harm done if a racing interrupt already did this */
  		local_irq_save(flags);
  		pagevec_move_tail(pvec);
  		local_irq_restore(flags);
  	}

  	pvec = &per_cpu(lru_deactivate_file_pvecs, cpu);

  	if (pagevec_count(pvec))

  		pagevec_lru_move_fn(pvec, lru_deactivate_file_fn, NULL);

  	pvec = &per_cpu(lru_lazyfree_pvecs, cpu);

  	if (pagevec_count(pvec))

  		pagevec_lru_move_fn(pvec, lru_lazyfree_fn, NULL);

  	activate_page_drain(cpu);

  }
  
  /**

   * deactivate_file_page - forcefully deactivate a file page

   * @page: page to deactivate
   *
   * This function hints the VM that @page is a good reclaim candidate,
   * for example if its invalidation fails due to the page being dirty
   * or under writeback.
   */

  void deactivate_file_page(struct page *page)

  {

  	/*

  	 * In a workload with many unevictable page such as mprotect,
  	 * unevictable page deactivation for accelerating reclaim is pointless.

  	 */
  	if (PageUnevictable(page))
  		return;

  	if (likely(get_page_unless_zero(page))) {

  		struct pagevec *pvec = &get_cpu_var(lru_deactivate_file_pvecs);

  		if (!pagevec_add(pvec, page) || PageCompound(page))

  			pagevec_lru_move_fn(pvec, lru_deactivate_file_fn, NULL);
  		put_cpu_var(lru_deactivate_file_pvecs);

  	}

  }

  /**

   * mark_page_lazyfree - make an anon page lazyfree

   * @page: page to deactivate
   *

   * mark_page_lazyfree() moves @page to the inactive file list.
   * This is done to accelerate the reclaim of @page.

   */

  void mark_page_lazyfree(struct page *page)

  {

  	if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) &&

  	    !PageSwapCache(page) && !PageUnevictable(page)) {

  		struct pagevec *pvec = &get_cpu_var(lru_lazyfree_pvecs);

  		get_page(page);

  		if (!pagevec_add(pvec, page) || PageCompound(page))

  			pagevec_lru_move_fn(pvec, lru_lazyfree_fn, NULL);
  		put_cpu_var(lru_lazyfree_pvecs);

  	}
  }

  void lru_add_drain(void)
  {

  	lru_add_drain_cpu(get_cpu());

  	put_cpu();

  }

  static void lru_add_drain_per_cpu(struct work_struct *dummy)

  {
  	lru_add_drain();
  }

  static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work);

  void lru_add_drain_all_cpuslocked(void)

  {

  	static DEFINE_MUTEX(lock);
  	static struct cpumask has_work;
  	int cpu;

  	/*
  	 * Make sure nobody triggers this path before mm_percpu_wq is fully
  	 * initialized.
  	 */
  	if (WARN_ON(!mm_percpu_wq))
  		return;

  	mutex_lock(&lock);

  	cpumask_clear(&has_work);
  
  	for_each_online_cpu(cpu) {
  		struct work_struct *work = &per_cpu(lru_add_drain_work, cpu);
  
  		if (pagevec_count(&per_cpu(lru_add_pvec, cpu)) ||
  		    pagevec_count(&per_cpu(lru_rotate_pvecs, cpu)) ||

  		    pagevec_count(&per_cpu(lru_deactivate_file_pvecs, cpu)) ||

  		    pagevec_count(&per_cpu(lru_lazyfree_pvecs, cpu)) ||

  		    need_activate_page_drain(cpu)) {
  			INIT_WORK(work, lru_add_drain_per_cpu);

  			queue_work_on(cpu, mm_percpu_wq, work);

  			cpumask_set_cpu(cpu, &has_work);
  		}
  	}
  
  	for_each_cpu(cpu, &has_work)
  		flush_work(&per_cpu(lru_add_drain_work, cpu));

  	mutex_unlock(&lock);

  }

  void lru_add_drain_all(void)
  {
  	get_online_cpus();
  	lru_add_drain_all_cpuslocked();
  	put_online_cpus();
  }

  /**

   * release_pages - batched put_page()

   * @pages: array of pages to release
   * @nr: number of pages
   * @cold: whether the pages are cache cold

   *

   * Decrement the reference count on all the pages in @pages.  If it
   * fell to zero, remove the page from the LRU and free it.

   */

  void release_pages(struct page **pages, int nr, bool cold)

  {
  	int i;

  	LIST_HEAD(pages_to_free);

  	struct pglist_data *locked_pgdat = NULL;

  	struct lruvec *lruvec;

  	unsigned long uninitialized_var(flags);

  	unsigned int uninitialized_var(lock_batch);

  	for (i = 0; i < nr; i++) {
  		struct page *page = pages[i];

  		/*
  		 * Make sure the IRQ-safe lock-holding time does not get
  		 * excessive with a continuous string of pages from the

  		 * same pgdat. The lock is held only if pgdat != NULL.

  		 */

  		if (locked_pgdat && ++lock_batch == SWAP_CLUSTER_MAX) {
  			spin_unlock_irqrestore(&locked_pgdat->lru_lock, flags);
  			locked_pgdat = NULL;

  		}

  		if (is_huge_zero_page(page))

  			continue;

  		/* Device public page can not be huge page */
  		if (is_device_public_page(page)) {
  			if (locked_pgdat) {
  				spin_unlock_irqrestore(&locked_pgdat->lru_lock,
  						       flags);
  				locked_pgdat = NULL;
  			}
  			put_zone_device_private_or_public_page(page);
  			continue;
  		}

  		page = compound_head(page);

  		if (!put_page_testzero(page))

  			continue;

  		if (PageCompound(page)) {

  			if (locked_pgdat) {
  				spin_unlock_irqrestore(&locked_pgdat->lru_lock, flags);
  				locked_pgdat = NULL;

  			}
  			__put_compound_page(page);
  			continue;
  		}

  		if (PageLRU(page)) {

  			struct pglist_data *pgdat = page_pgdat(page);

  			if (pgdat != locked_pgdat) {
  				if (locked_pgdat)
  					spin_unlock_irqrestore(&locked_pgdat->lru_lock,

  									flags);

  				lock_batch = 0;

  				locked_pgdat = pgdat;
  				spin_lock_irqsave(&locked_pgdat->lru_lock, flags);

  			}

  			lruvec = mem_cgroup_page_lruvec(page, locked_pgdat);

  			VM_BUG_ON_PAGE(!PageLRU(page), page);

  			__ClearPageLRU(page);

  			del_page_from_lru_list(page, lruvec, page_off_lru(page));

  		}

  		/* Clear Active bit in case of parallel mark_page_accessed */

  		__ClearPageActive(page);

  		__ClearPageWaiters(page);

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

  	}

  	if (locked_pgdat)
  		spin_unlock_irqrestore(&locked_pgdat->lru_lock, flags);

  	mem_cgroup_uncharge_list(&pages_to_free);

  	free_hot_cold_page_list(&pages_to_free, cold);

  }

  EXPORT_SYMBOL(release_pages);

  
  /*
   * The pages which we're about to release may be in the deferred lru-addition
   * queues.  That would prevent them from really being freed right now.  That's
   * OK from a correctness point of view but is inefficient - those pages may be
   * cache-warm and we want to give them back to the page allocator ASAP.
   *
   * So __pagevec_release() will drain those queues here.  __pagevec_lru_add()
   * and __pagevec_lru_add_active() call release_pages() directly to avoid
   * mutual recursion.
   */
  void __pagevec_release(struct pagevec *pvec)
  {
  	lru_add_drain();
  	release_pages(pvec->pages, pagevec_count(pvec), pvec->cold);
  	pagevec_reinit(pvec);
  }

  EXPORT_SYMBOL(__pagevec_release);

  #ifdef CONFIG_TRANSPARENT_HUGEPAGE

  /* used by __split_huge_page_refcount() */

  void lru_add_page_tail(struct page *page, struct page *page_tail,

  		       struct lruvec *lruvec, struct list_head *list)

  {

  	const int file = 0;

  	VM_BUG_ON_PAGE(!PageHead(page), page);
  	VM_BUG_ON_PAGE(PageCompound(page_tail), page);
  	VM_BUG_ON_PAGE(PageLRU(page_tail), page);

  	VM_BUG_ON(NR_CPUS != 1 &&

  		  !spin_is_locked(&lruvec_pgdat(lruvec)->lru_lock));

  	if (!list)
  		SetPageLRU(page_tail);

  	if (likely(PageLRU(page)))
  		list_add_tail(&page_tail->lru, &page->lru);

  	else if (list) {
  		/* page reclaim is reclaiming a huge page */
  		get_page(page_tail);
  		list_add_tail(&page_tail->lru, list);
  	} else {

  		struct list_head *list_head;
  		/*
  		 * Head page has not yet been counted, as an hpage,
  		 * so we must account for each subpage individually.
  		 *
  		 * Use the standard add function to put page_tail on the list,
  		 * but then correct its position so they all end up in order.
  		 */

  		add_page_to_lru_list(page_tail, lruvec, page_lru(page_tail));

  		list_head = page_tail->lru.prev;
  		list_move_tail(&page_tail->lru, list_head);

  	}

  
  	if (!PageUnevictable(page))

  		update_page_reclaim_stat(lruvec, file, PageActive(page_tail));

  }

  #endif /* CONFIG_TRANSPARENT_HUGEPAGE */

  static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
  				 void *arg)

  {

  	int file = page_is_file_cache(page);
  	int active = PageActive(page);
  	enum lru_list lru = page_lru(page);

  	VM_BUG_ON_PAGE(PageLRU(page), page);

  
  	SetPageLRU(page);

  	add_page_to_lru_list(page, lruvec, lru);
  	update_page_reclaim_stat(lruvec, file, active);

  	trace_mm_lru_insertion(page, lru);

  }

  /*

   * Add the passed pages to the LRU, then drop the caller's refcount
   * on them.  Reinitialises the caller's pagevec.
   */

  void __pagevec_lru_add(struct pagevec *pvec)

  {

  	pagevec_lru_move_fn(pvec, __pagevec_lru_add_fn, NULL);

  }

  EXPORT_SYMBOL(__pagevec_lru_add);

  /**

   * pagevec_lookup_entries - gang pagecache lookup
   * @pvec:	Where the resulting entries are placed
   * @mapping:	The address_space to search
   * @start:	The starting entry index
   * @nr_entries:	The maximum number of entries
   * @indices:	The cache indices corresponding to the entries in @pvec
   *
   * pagevec_lookup_entries() will search for and return a group of up
   * to @nr_entries pages and shadow entries in the mapping.  All
   * entries are placed in @pvec.  pagevec_lookup_entries() takes a
   * reference against actual pages in @pvec.
   *
   * The search returns a group of mapping-contiguous entries with
   * ascending indexes.  There may be holes in the indices due to
   * not-present entries.
   *
   * pagevec_lookup_entries() returns the number of entries which were
   * found.
   */
  unsigned pagevec_lookup_entries(struct pagevec *pvec,
  				struct address_space *mapping,
  				pgoff_t start, unsigned nr_pages,
  				pgoff_t *indices)
  {
  	pvec->nr = find_get_entries(mapping, start, nr_pages,
  				    pvec->pages, indices);
  	return pagevec_count(pvec);
  }
  
  /**
   * pagevec_remove_exceptionals - pagevec exceptionals pruning
   * @pvec:	The pagevec to prune
   *
   * pagevec_lookup_entries() fills both pages and exceptional radix
   * tree entries into the pagevec.  This function prunes all
   * exceptionals from @pvec without leaving holes, so that it can be
   * passed on to page-only pagevec operations.
   */
  void pagevec_remove_exceptionals(struct pagevec *pvec)
  {
  	int i, j;
  
  	for (i = 0, j = 0; i < pagevec_count(pvec); i++) {
  		struct page *page = pvec->pages[i];
  		if (!radix_tree_exceptional_entry(page))
  			pvec->pages[j++] = page;
  	}
  	pvec->nr = j;
  }
  
  /**

   * pagevec_lookup_range - gang pagecache lookup

   * @pvec:	Where the resulting pages are placed
   * @mapping:	The address_space to search
   * @start:	The starting page index

   * @end:	The final page index

   * @nr_pages:	The maximum number of pages
   *

   * pagevec_lookup_range() will search for and return a group of up to @nr_pages
   * pages in the mapping starting from index @start and upto index @end
   * (inclusive).  The pages are placed in @pvec.  pagevec_lookup() takes a

   * reference against the pages in @pvec.
   *
   * The search returns a group of mapping-contiguous pages with ascending

   * indexes.  There may be holes in the indices due to not-present pages. We
   * also update @start to index the next page for the traversal.

   *

   * pagevec_lookup_range() returns the number of pages which were found. If this
   * number is smaller than @nr_pages, the end of specified range has been
   * reached.

   */

  unsigned pagevec_lookup_range(struct pagevec *pvec,

  		struct address_space *mapping, pgoff_t *start, pgoff_t end)

  {

  	pvec->nr = find_get_pages_range(mapping, start, end, PAGEVEC_SIZE,

  					pvec->pages);

  	return pagevec_count(pvec);
  }

  EXPORT_SYMBOL(pagevec_lookup_range);

  unsigned pagevec_lookup_tag(struct pagevec *pvec, struct address_space *mapping,
  		pgoff_t *index, int tag, unsigned nr_pages)
  {
  	pvec->nr = find_get_pages_tag(mapping, index, tag,
  					nr_pages, pvec->pages);
  	return pagevec_count(pvec);
  }

  EXPORT_SYMBOL(pagevec_lookup_tag);

  /*
   * Perform any setup for the swap system
   */
  void __init swap_setup(void)
  {

  	unsigned long megs = totalram_pages >> (20 - PAGE_SHIFT);

  	/* Use a smaller cluster for small-memory machines */
  	if (megs < 16)
  		page_cluster = 2;
  	else
  		page_cluster = 3;
  	/*
  	 * Right now other parts of the system means that we
  	 * _really_ don't want to cluster much more
  	 */

  }