mm/swap.c - kernel/msm - Gitiles

 /*
  *  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/module.h>
 #include <linux/mm_inline.h>
 #include <linux/buffer_head.h>	/* for try_to_release_page() */
 #include <linux/percpu_counter.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 "internal.h"

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

 static DEFINE_PER_CPU(struct pagevec[NR_LRU_LISTS], lru_add_pvecs);
 static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);
 static DEFINE_PER_CPU(struct pagevec, lru_deactivate_pvecs);

 /*
  * 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)) {
 		unsigned long flags;
 		struct zone *zone = page_zone(page);

 		spin_lock_irqsave(&zone->lru_lock, flags);
 		VM_BUG_ON(!PageLRU(page));
 		__ClearPageLRU(page);
 		del_page_from_lru(zone, page);
 		spin_unlock_irqrestore(&zone->lru_lock, flags);
 	}
 }

 static void __put_single_page(struct page *page)
 {
 	__page_cache_release(page);
 	free_hot_cold_page(page, 0);
 }

 static void __put_compound_page(struct page *page)
 {
 	compound_page_dtor *dtor;

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

 static void put_compound_page(struct page *page)
 {
 	if (unlikely(PageTail(page))) {
 		/* __split_huge_page_refcount can run under us */
 		struct page *page_head = compound_trans_head(page);

 		if (likely(page != page_head &&
 			   get_page_unless_zero(page_head))) {
 			unsigned long flags;
 			/*
 			 * page_head wasn't a dangling pointer but it
 			 * may not be a head page anymore by the time
 			 * we obtain the lock. That is ok as long as it
 			 * can't be freed from under us.
 			 */
 			flags = compound_lock_irqsave(page_head);
 			if (unlikely(!PageTail(page))) {
 				/* __split_huge_page_refcount run before us */
 				compound_unlock_irqrestore(page_head, flags);
 				VM_BUG_ON(PageHead(page_head));
 				if (put_page_testzero(page_head))
 					__put_single_page(page_head);
 			out_put_single:
 				if (put_page_testzero(page))
 					__put_single_page(page);
 				return;
 			}
 			VM_BUG_ON(page_head != page->first_page);
 			/*
 			 * We can release the refcount taken by
 			 * get_page_unless_zero() now that
 			 * __split_huge_page_refcount() is blocked on
 			 * the compound_lock.
 			 */
 			if (put_page_testzero(page_head))
 				VM_BUG_ON(1);
 			/* __split_huge_page_refcount will wait now */
 			VM_BUG_ON(page_mapcount(page) <= 0);
 			atomic_dec(&page->_mapcount);
 			VM_BUG_ON(atomic_read(&page_head->_count) <= 0);
 			VM_BUG_ON(atomic_read(&page->_count) != 0);
 			compound_unlock_irqrestore(page_head, flags);
 			if (put_page_testzero(page_head)) {
 				if (PageHead(page_head))
 					__put_compound_page(page_head);
 				else
 					__put_single_page(page_head);
 			}
 		} else {
 			/* page_head is a dangling pointer */
 			VM_BUG_ON(PageTail(page));
 			goto out_put_single;
 		}
 	} else if (put_page_testzero(page)) {
 		if (PageHead(page))
 			__put_compound_page(page);
 		else
 			__put_single_page(page);
 	}
 }

 void put_page(struct page *page)
 {
 	if (unlikely(PageCompound(page)))
 		put_compound_page(page);
 	else if (put_page_testzero(page))
 		__put_single_page(page);
 }
 EXPORT_SYMBOL(put_page);

 /*
  * This function is exported but must not be called by anything other
  * than get_page(). It implements the slow path of get_page().
  */
 bool __get_page_tail(struct page *page)
 {
 	/*
 	 * This takes care of get_page() if run on a tail page
 	 * returned by one of the get_user_pages/follow_page variants.
 	 * get_user_pages/follow_page itself doesn't need the compound
 	 * lock because it runs __get_page_tail_foll() under the
 	 * proper PT lock that already serializes against
 	 * split_huge_page().
 	 */
 	unsigned long flags;
 	bool got = false;
 	struct page *page_head = compound_trans_head(page);

 	if (likely(page != page_head && get_page_unless_zero(page_head))) {
 		/*
 		 * page_head wasn't a dangling pointer but it
 		 * may not be a head page anymore by the time
 		 * we obtain the lock. That is ok as long as it
 		 * can't be freed from under us.
 		 */
 		flags = compound_lock_irqsave(page_head);
 		/* here __split_huge_page_refcount won't run anymore */
 		if (likely(PageTail(page))) {
 			__get_page_tail_foll(page, false);
 			got = true;
 		}
 		compound_unlock_irqrestore(page_head, flags);
 		if (unlikely(!got))
 			put_page(page_head);
 	}
 	return got;
 }
 EXPORT_SYMBOL(__get_page_tail);

 /**
  * 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);
 		page_cache_release(victim);
 	}
 }
 EXPORT_SYMBOL(put_pages_list);

 static void pagevec_lru_move_fn(struct pagevec *pvec,
 				void (*move_fn)(struct page *page, void *arg),
 				void *arg)
 {
 	int i;
 	struct zone *zone = NULL;
 	unsigned long flags = 0;

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

 		if (pagezone != zone) {
 			if (zone)
 				spin_unlock_irqrestore(&zone->lru_lock, flags);
 			zone = pagezone;
 			spin_lock_irqsave(&zone->lru_lock, flags);
 		}

 		(*move_fn)(page, arg);
 	}
 	if (zone)
 		spin_unlock_irqrestore(&zone->lru_lock, flags);
 	release_pages(pvec->pages, pvec->nr, pvec->cold);
 	pagevec_reinit(pvec);
 }

 static void pagevec_move_tail_fn(struct page *page, void *arg)
 {
 	int *pgmoved = arg;
 	struct zone *zone = page_zone(page);

 	if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
 		enum lru_list lru = page_lru_base_type(page);
 		list_move_tail(&page->lru, &zone->lru[lru].list);
 		mem_cgroup_rotate_reclaimable_page(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) && !PageActive(page) &&
 	    !PageUnevictable(page) && PageLRU(page)) {
 		struct pagevec *pvec;
 		unsigned long flags;

 		page_cache_get(page);
 		local_irq_save(flags);
 		pvec = &__get_cpu_var(lru_rotate_pvecs);
 		if (!pagevec_add(pvec, page))
 			pagevec_move_tail(pvec);
 		local_irq_restore(flags);
 	}
 }

 static void update_page_reclaim_stat(struct zone *zone, struct page *page,
 				     int file, int rotated)
 {
 	struct zone_reclaim_stat *reclaim_stat = &zone->reclaim_stat;
 	struct zone_reclaim_stat *memcg_reclaim_stat;

 	memcg_reclaim_stat = mem_cgroup_get_reclaim_stat_from_page(page);

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

 	if (!memcg_reclaim_stat)
 		return;

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

 static void __activate_page(struct page *page, void *arg)
 {
 	struct zone *zone = page_zone(page);

 	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(zone, page, lru);

 		SetPageActive(page);
 		lru += LRU_ACTIVE;
 		add_page_to_lru_list(zone, page, lru);
 		__count_vm_event(PGACTIVATE);

 		update_page_reclaim_stat(zone, page, file, 1);
 	}
 }

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

 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);
 }

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

 		page_cache_get(page);
 		if (!pagevec_add(pvec, page))
 			pagevec_lru_move_fn(pvec, __activate_page, NULL);
 		put_cpu_var(activate_page_pvecs);
 	}
 }

 #else
 static inline void activate_page_drain(int cpu)
 {
 }

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

 	spin_lock_irq(&zone->lru_lock);
 	__activate_page(page, NULL);
 	spin_unlock_irq(&zone->lru_lock);
 }
 #endif

 /*
  * Mark a page as having seen activity.
  *
  * inactive,unreferenced	->	inactive,referenced
  * inactive,referenced		->	active,unreferenced
  * active,unreferenced		->	active,referenced
  */
 void mark_page_accessed(struct page *page)
 {
 	if (!PageActive(page) && !PageUnevictable(page) &&
 			PageReferenced(page) && PageLRU(page)) {
 		activate_page(page);
 		ClearPageReferenced(page);
 	} else if (!PageReferenced(page)) {
 		SetPageReferenced(page);
 	}
 }

 EXPORT_SYMBOL(mark_page_accessed);

 void __lru_cache_add(struct page *page, enum lru_list lru)
 {
 	struct pagevec *pvec = &get_cpu_var(lru_add_pvecs)[lru];

 	page_cache_get(page);
 	if (!pagevec_add(pvec, page))
 		____pagevec_lru_add(pvec, lru);
 	put_cpu_var(lru_add_pvecs);
 }
 EXPORT_SYMBOL(__lru_cache_add);

 /**
  * lru_cache_add_lru - add a page to a page list
  * @page: the page to be added to the LRU.
  * @lru: the LRU list to which the page is added.
  */
 void lru_cache_add_lru(struct page *page, enum lru_list lru)
 {
 	if (PageActive(page)) {
 		VM_BUG_ON(PageUnevictable(page));
 		ClearPageActive(page);
 	} else if (PageUnevictable(page)) {
 		VM_BUG_ON(PageActive(page));
 		ClearPageUnevictable(page);
 	}

 	VM_BUG_ON(PageLRU(page) || PageActive(page) || PageUnevictable(page));
 	__lru_cache_add(page, lru);
 }

 /**
  * 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 zone *zone = page_zone(page);

 	spin_lock_irq(&zone->lru_lock);
 	SetPageUnevictable(page);
 	SetPageLRU(page);
 	add_page_to_lru_list(zone, page, LRU_UNEVICTABLE);
 	spin_unlock_irq(&zone->lru_lock);
 }

 /*
  * 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_fn(struct page *page, void *arg)
 {
 	int lru, file;
 	bool active;
 	struct zone *zone = page_zone(page);

 	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(zone, page, lru + active);
 	ClearPageActive(page);
 	ClearPageReferenced(page);
 	add_page_to_lru_list(zone, page, 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, &zone->lru[lru].list);
 		mem_cgroup_rotate_reclaimable_page(page);
 		__count_vm_event(PGROTATED);
 	}

 	if (active)
 		__count_vm_event(PGDEACTIVATE);
 	update_page_reclaim_stat(zone, page, file, 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.
  */
 static void drain_cpu_pagevecs(int cpu)
 {
 	struct pagevec *pvecs = per_cpu(lru_add_pvecs, cpu);
 	struct pagevec *pvec;
 	int lru;

 	for_each_lru(lru) {
 		pvec = &pvecs[lru - LRU_BASE];
 		if (pagevec_count(pvec))
 			____pagevec_lru_add(pvec, lru);
 	}

 	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_pvecs, cpu);
 	if (pagevec_count(pvec))
 		pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);

 	activate_page_drain(cpu);
 }

 /**
  * deactivate_page - forcefully deactivate a 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_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_pvecs);

 		if (!pagevec_add(pvec, page))
 			pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
 		put_cpu_var(lru_deactivate_pvecs);
 	}
 }

 void lru_add_drain(void)
 {
 	drain_cpu_pagevecs(get_cpu());
 	put_cpu();
 }

 static void lru_add_drain_per_cpu(struct work_struct *dummy)
 {
 	lru_add_drain();
 }

 /*
  * Returns 0 for success
  */
 int lru_add_drain_all(void)
 {
 	return schedule_on_each_cpu(lru_add_drain_per_cpu);
 }

 /*
  * Batched page_cache_release().  Decrement the reference count on all the
  * passed pages.  If it fell to zero then remove the page from the LRU and
  * free it.
  *
  * Avoid taking zone->lru_lock if possible, but if it is taken, retain it
  * for the remainder of the operation.
  *
  * The locking in this function is against shrink_inactive_list(): we recheck
  * the page count inside the lock to see whether shrink_inactive_list()
  * grabbed the page via the LRU.  If it did, give up: shrink_inactive_list()
  * will free it.
  */
 void release_pages(struct page **pages, int nr, int cold)
 {
 	int i;
 	struct pagevec pages_to_free;
 	struct zone *zone = NULL;
 	unsigned long uninitialized_var(flags);

 	pagevec_init(&pages_to_free, cold);
 	for (i = 0; i < nr; i++) {
 		struct page *page = pages[i];

 		if (unlikely(PageCompound(page))) {
 			if (zone) {
 				spin_unlock_irqrestore(&zone->lru_lock, flags);
 				zone = NULL;
 			}
 			put_compound_page(page);
 			continue;
 		}

 		if (!put_page_testzero(page))
 			continue;

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

 			if (pagezone != zone) {
 				if (zone)
 					spin_unlock_irqrestore(&zone->lru_lock,
 									flags);
 				zone = pagezone;
 				spin_lock_irqsave(&zone->lru_lock, flags);
 			}
 			VM_BUG_ON(!PageLRU(page));
 			__ClearPageLRU(page);
 			del_page_from_lru(zone, page);
 		}

 		if (!pagevec_add(&pages_to_free, page)) {
 			if (zone) {
 				spin_unlock_irqrestore(&zone->lru_lock, flags);
 				zone = NULL;
 			}
 			__pagevec_free(&pages_to_free);
 			pagevec_reinit(&pages_to_free);
   		}
 	}
 	if (zone)
 		spin_unlock_irqrestore(&zone->lru_lock, flags);

 	pagevec_free(&pages_to_free);
 }
 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);

 /* used by __split_huge_page_refcount() */
 void lru_add_page_tail(struct zone* zone,
 		       struct page *page, struct page *page_tail)
 {
 	int active;
 	enum lru_list lru;
 	const int file = 0;
 	struct list_head *head;

 	VM_BUG_ON(!PageHead(page));
 	VM_BUG_ON(PageCompound(page_tail));
 	VM_BUG_ON(PageLRU(page_tail));
 	VM_BUG_ON(!spin_is_locked(&zone->lru_lock));

 	SetPageLRU(page_tail);

 	if (page_evictable(page_tail, NULL)) {
 		if (PageActive(page)) {
 			SetPageActive(page_tail);
 			active = 1;
 			lru = LRU_ACTIVE_ANON;
 		} else {
 			active = 0;
 			lru = LRU_INACTIVE_ANON;
 		}
 		update_page_reclaim_stat(zone, page_tail, file, active);
 		if (likely(PageLRU(page)))
 			head = page->lru.prev;
 		else
 			head = &zone->lru[lru].list;
 		__add_page_to_lru_list(zone, page_tail, lru, head);
 	} else {
 		SetPageUnevictable(page_tail);
 		add_page_to_lru_list(zone, page_tail, LRU_UNEVICTABLE);
 	}
 }

 static void ____pagevec_lru_add_fn(struct page *page, void *arg)
 {
 	enum lru_list lru = (enum lru_list)arg;
 	struct zone *zone = page_zone(page);
 	int file = is_file_lru(lru);
 	int active = is_active_lru(lru);

 	VM_BUG_ON(PageActive(page));
 	VM_BUG_ON(PageUnevictable(page));
 	VM_BUG_ON(PageLRU(page));

 	SetPageLRU(page);
 	if (active)
 		SetPageActive(page);
 	update_page_reclaim_stat(zone, page, file, active);
 	add_page_to_lru_list(zone, 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, enum lru_list lru)
 {
 	VM_BUG_ON(is_unevictable_lru(lru));

 	pagevec_lru_move_fn(pvec, ____pagevec_lru_add_fn, (void *)lru);
 }

 EXPORT_SYMBOL(____pagevec_lru_add);

 /*
  * Try to drop buffers from the pages in a pagevec
  */
 void pagevec_strip(struct pagevec *pvec)
 {
 	int i;

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

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

 /**
  * pagevec_lookup - gang pagecache lookup
  * @pvec:	Where the resulting pages are placed
  * @mapping:	The address_space to search
  * @start:	The starting page index
  * @nr_pages:	The maximum number of pages
  *
  * pagevec_lookup() will search for and return a group of up to @nr_pages pages
  * in the mapping.  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.
  *
  * pagevec_lookup() returns the number of pages which were found.
  */
 unsigned pagevec_lookup(struct pagevec *pvec, struct address_space *mapping,
 		pgoff_t start, unsigned nr_pages)
 {
 	pvec->nr = find_get_pages(mapping, start, nr_pages, pvec->pages);
 	return pagevec_count(pvec);
 }

 EXPORT_SYMBOL(pagevec_lookup);

 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);

 #ifdef CONFIG_SWAP
 	bdi_init(swapper_space.backing_dev_info);
 #endif

 	/* 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
 	 */
 }
	/*
	* 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/module.h>
	#include <linux/mm_inline.h>
	#include <linux/buffer_head.h> /* for try_to_release_page() */
	#include <linux/percpu_counter.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 "internal.h"

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

	static DEFINE_PER_CPU(struct pagevec[NR_LRU_LISTS], lru_add_pvecs);
	static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);
	static DEFINE_PER_CPU(struct pagevec, lru_deactivate_pvecs);

	/*
	* 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)) {
	unsigned long flags;
	struct zone *zone = page_zone(page);

	spin_lock_irqsave(&zone->lru_lock, flags);
	VM_BUG_ON(!PageLRU(page));
	__ClearPageLRU(page);
	del_page_from_lru(zone, page);
	spin_unlock_irqrestore(&zone->lru_lock, flags);
	}
	}

	static void __put_single_page(struct page *page)
	{
	__page_cache_release(page);
	free_hot_cold_page(page, 0);
	}

	static void __put_compound_page(struct page *page)
	{
	compound_page_dtor *dtor;

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

	static void put_compound_page(struct page *page)
	{
	if (unlikely(PageTail(page))) {
	/* __split_huge_page_refcount can run under us */
	struct page *page_head = compound_trans_head(page);

	if (likely(page != page_head &&
	get_page_unless_zero(page_head))) {
	unsigned long flags;
	/*
	* page_head wasn't a dangling pointer but it
	* may not be a head page anymore by the time
	* we obtain the lock. That is ok as long as it
	* can't be freed from under us.
	*/
	flags = compound_lock_irqsave(page_head);
	if (unlikely(!PageTail(page))) {
	/* __split_huge_page_refcount run before us */
	compound_unlock_irqrestore(page_head, flags);
	VM_BUG_ON(PageHead(page_head));
	if (put_page_testzero(page_head))
	__put_single_page(page_head);
	out_put_single:
	if (put_page_testzero(page))
	__put_single_page(page);
	return;
	}
	VM_BUG_ON(page_head != page->first_page);
	/*
	* We can release the refcount taken by
	* get_page_unless_zero() now that
	* __split_huge_page_refcount() is blocked on
	* the compound_lock.
	*/
	if (put_page_testzero(page_head))
	VM_BUG_ON(1);
	/* __split_huge_page_refcount will wait now */
	VM_BUG_ON(page_mapcount(page) <= 0);
	atomic_dec(&page->_mapcount);
	VM_BUG_ON(atomic_read(&page_head->_count) <= 0);
	VM_BUG_ON(atomic_read(&page->_count) != 0);
	compound_unlock_irqrestore(page_head, flags);
	if (put_page_testzero(page_head)) {
	if (PageHead(page_head))
	__put_compound_page(page_head);
	else
	__put_single_page(page_head);
	}
	} else {
	/* page_head is a dangling pointer */
	VM_BUG_ON(PageTail(page));
	goto out_put_single;
	}
	} else if (put_page_testzero(page)) {
	if (PageHead(page))
	__put_compound_page(page);
	else
	__put_single_page(page);
	}
	}

	void put_page(struct page *page)
	{
	if (unlikely(PageCompound(page)))
	put_compound_page(page);
	else if (put_page_testzero(page))
	__put_single_page(page);
	}
	EXPORT_SYMBOL(put_page);

	/*
	* This function is exported but must not be called by anything other
	* than get_page(). It implements the slow path of get_page().
	*/
	bool __get_page_tail(struct page *page)
	{
	/*
	* This takes care of get_page() if run on a tail page
	* returned by one of the get_user_pages/follow_page variants.
	* get_user_pages/follow_page itself doesn't need the compound
	* lock because it runs __get_page_tail_foll() under the
	* proper PT lock that already serializes against
	* split_huge_page().
	*/
	unsigned long flags;
	bool got = false;
	struct page *page_head = compound_trans_head(page);

	if (likely(page != page_head && get_page_unless_zero(page_head))) {
	/*
	* page_head wasn't a dangling pointer but it
	* may not be a head page anymore by the time
	* we obtain the lock. That is ok as long as it
	* can't be freed from under us.
	*/
	flags = compound_lock_irqsave(page_head);
	/* here __split_huge_page_refcount won't run anymore */
	if (likely(PageTail(page))) {
	__get_page_tail_foll(page, false);
	got = true;
	}
	compound_unlock_irqrestore(page_head, flags);
	if (unlikely(!got))
	put_page(page_head);
	}
	return got;
	}
	EXPORT_SYMBOL(__get_page_tail);

	/**
	* 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);
	page_cache_release(victim);
	}
	}
	EXPORT_SYMBOL(put_pages_list);

	static void pagevec_lru_move_fn(struct pagevec *pvec,
	void (move_fn)(struct page page, void *arg),
	void *arg)
	{
	int i;
	struct zone *zone = NULL;
	unsigned long flags = 0;

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

	if (pagezone != zone) {
	if (zone)
	spin_unlock_irqrestore(&zone->lru_lock, flags);
	zone = pagezone;
	spin_lock_irqsave(&zone->lru_lock, flags);
	}

	(*move_fn)(page, arg);
	}
	if (zone)
	spin_unlock_irqrestore(&zone->lru_lock, flags);
	release_pages(pvec->pages, pvec->nr, pvec->cold);
	pagevec_reinit(pvec);
	}

	static void pagevec_move_tail_fn(struct page page, void arg)
	{
	int *pgmoved = arg;
	struct zone *zone = page_zone(page);

	if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
	enum lru_list lru = page_lru_base_type(page);
	list_move_tail(&page->lru, &zone->lru[lru].list);
	mem_cgroup_rotate_reclaimable_page(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) && !PageActive(page) &&
	!PageUnevictable(page) && PageLRU(page)) {
	struct pagevec *pvec;
	unsigned long flags;

	page_cache_get(page);
	local_irq_save(flags);
	pvec = &__get_cpu_var(lru_rotate_pvecs);
	if (!pagevec_add(pvec, page))
	pagevec_move_tail(pvec);
	local_irq_restore(flags);
	}
	}

	static void update_page_reclaim_stat(struct zone zone, struct page page,
	int file, int rotated)
	{
	struct zone_reclaim_stat *reclaim_stat = &zone->reclaim_stat;
	struct zone_reclaim_stat *memcg_reclaim_stat;

	memcg_reclaim_stat = mem_cgroup_get_reclaim_stat_from_page(page);

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

	if (!memcg_reclaim_stat)
	return;

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

	static void __activate_page(struct page page, void arg)
	{
	struct zone *zone = page_zone(page);

	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(zone, page, lru);

	SetPageActive(page);
	lru += LRU_ACTIVE;
	add_page_to_lru_list(zone, page, lru);
	__count_vm_event(PGACTIVATE);

	update_page_reclaim_stat(zone, page, file, 1);
	}
	}

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

	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);
	}

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

	page_cache_get(page);
	if (!pagevec_add(pvec, page))
	pagevec_lru_move_fn(pvec, __activate_page, NULL);
	put_cpu_var(activate_page_pvecs);
	}
	}

	#else
	static inline void activate_page_drain(int cpu)
	{
	}

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

	spin_lock_irq(&zone->lru_lock);
	__activate_page(page, NULL);
	spin_unlock_irq(&zone->lru_lock);
	}
	#endif

	/*
	* Mark a page as having seen activity.
	*
	* inactive,unreferenced -> inactive,referenced
	* inactive,referenced -> active,unreferenced
	* active,unreferenced -> active,referenced
	*/
	void mark_page_accessed(struct page *page)
	{
	if (!PageActive(page) && !PageUnevictable(page) &&
	PageReferenced(page) && PageLRU(page)) {
	activate_page(page);
	ClearPageReferenced(page);
	} else if (!PageReferenced(page)) {
	SetPageReferenced(page);
	}
	}

	EXPORT_SYMBOL(mark_page_accessed);

	void __lru_cache_add(struct page *page, enum lru_list lru)
	{
	struct pagevec *pvec = &get_cpu_var(lru_add_pvecs)[lru];

	page_cache_get(page);
	if (!pagevec_add(pvec, page))
	____pagevec_lru_add(pvec, lru);
	put_cpu_var(lru_add_pvecs);
	}
	EXPORT_SYMBOL(__lru_cache_add);

	/**
	* lru_cache_add_lru - add a page to a page list
	* @page: the page to be added to the LRU.
	* @lru: the LRU list to which the page is added.
	*/
	void lru_cache_add_lru(struct page *page, enum lru_list lru)
	{
	if (PageActive(page)) {
	VM_BUG_ON(PageUnevictable(page));
	ClearPageActive(page);
	} else if (PageUnevictable(page)) {
	VM_BUG_ON(PageActive(page));
	ClearPageUnevictable(page);
	}

	VM_BUG_ON(PageLRU(page) \|\| PageActive(page) \|\| PageUnevictable(page));
	__lru_cache_add(page, lru);
	}

	/**
	* 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 zone *zone = page_zone(page);

	spin_lock_irq(&zone->lru_lock);
	SetPageUnevictable(page);
	SetPageLRU(page);
	add_page_to_lru_list(zone, page, LRU_UNEVICTABLE);
	spin_unlock_irq(&zone->lru_lock);
	}

	/*
	* 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_fn(struct page page, void arg)
	{
	int lru, file;
	bool active;
	struct zone *zone = page_zone(page);

	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(zone, page, lru + active);
	ClearPageActive(page);
	ClearPageReferenced(page);
	add_page_to_lru_list(zone, page, 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, &zone->lru[lru].list);
	mem_cgroup_rotate_reclaimable_page(page);
	__count_vm_event(PGROTATED);
	}

	if (active)
	__count_vm_event(PGDEACTIVATE);
	update_page_reclaim_stat(zone, page, file, 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.
	*/
	static void drain_cpu_pagevecs(int cpu)
	{
	struct pagevec *pvecs = per_cpu(lru_add_pvecs, cpu);
	struct pagevec *pvec;
	int lru;

	for_each_lru(lru) {
	pvec = &pvecs[lru - LRU_BASE];
	if (pagevec_count(pvec))
	____pagevec_lru_add(pvec, lru);
	}

	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_pvecs, cpu);
	if (pagevec_count(pvec))
	pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);

	activate_page_drain(cpu);
	}

	/**
	* deactivate_page - forcefully deactivate a 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_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_pvecs);

	if (!pagevec_add(pvec, page))
	pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
	put_cpu_var(lru_deactivate_pvecs);
	}
	}

	void lru_add_drain(void)
	{
	drain_cpu_pagevecs(get_cpu());
	put_cpu();
	}

	static void lru_add_drain_per_cpu(struct work_struct *dummy)
	{
	lru_add_drain();
	}

	/*
	* Returns 0 for success
	*/
	int lru_add_drain_all(void)
	{
	return schedule_on_each_cpu(lru_add_drain_per_cpu);
	}

	/*
	* Batched page_cache_release(). Decrement the reference count on all the
	* passed pages. If it fell to zero then remove the page from the LRU and
	* free it.
	*
	* Avoid taking zone->lru_lock if possible, but if it is taken, retain it
	* for the remainder of the operation.
	*
	* The locking in this function is against shrink_inactive_list(): we recheck
	* the page count inside the lock to see whether shrink_inactive_list()
	* grabbed the page via the LRU. If it did, give up: shrink_inactive_list()
	* will free it.
	*/
	void release_pages(struct page **pages, int nr, int cold)
	{
	int i;
	struct pagevec pages_to_free;
	struct zone *zone = NULL;
	unsigned long uninitialized_var(flags);

	pagevec_init(&pages_to_free, cold);
	for (i = 0; i < nr; i++) {
	struct page *page = pages[i];

	if (unlikely(PageCompound(page))) {
	if (zone) {
	spin_unlock_irqrestore(&zone->lru_lock, flags);
	zone = NULL;
	}
	put_compound_page(page);
	continue;
	}

	if (!put_page_testzero(page))
	continue;

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

	if (pagezone != zone) {
	if (zone)
	spin_unlock_irqrestore(&zone->lru_lock,
	flags);
	zone = pagezone;
	spin_lock_irqsave(&zone->lru_lock, flags);
	}
	VM_BUG_ON(!PageLRU(page));
	__ClearPageLRU(page);
	del_page_from_lru(zone, page);
	}

	if (!pagevec_add(&pages_to_free, page)) {
	if (zone) {
	spin_unlock_irqrestore(&zone->lru_lock, flags);
	zone = NULL;
	}
	__pagevec_free(&pages_to_free);
	pagevec_reinit(&pages_to_free);
	}
	}
	if (zone)
	spin_unlock_irqrestore(&zone->lru_lock, flags);

	pagevec_free(&pages_to_free);
	}
	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);

	/* used by __split_huge_page_refcount() */
	void lru_add_page_tail(struct zone* zone,
	struct page page, struct page page_tail)
	{
	int active;
	enum lru_list lru;
	const int file = 0;
	struct list_head *head;

	VM_BUG_ON(!PageHead(page));
	VM_BUG_ON(PageCompound(page_tail));
	VM_BUG_ON(PageLRU(page_tail));
	VM_BUG_ON(!spin_is_locked(&zone->lru_lock));

	SetPageLRU(page_tail);

	if (page_evictable(page_tail, NULL)) {
	if (PageActive(page)) {
	SetPageActive(page_tail);
	active = 1;
	lru = LRU_ACTIVE_ANON;
	} else {
	active = 0;
	lru = LRU_INACTIVE_ANON;
	}
	update_page_reclaim_stat(zone, page_tail, file, active);
	if (likely(PageLRU(page)))
	head = page->lru.prev;
	else
	head = &zone->lru[lru].list;
	__add_page_to_lru_list(zone, page_tail, lru, head);
	} else {
	SetPageUnevictable(page_tail);
	add_page_to_lru_list(zone, page_tail, LRU_UNEVICTABLE);
	}
	}

	static void ____pagevec_lru_add_fn(struct page page, void arg)
	{
	enum lru_list lru = (enum lru_list)arg;
	struct zone *zone = page_zone(page);
	int file = is_file_lru(lru);
	int active = is_active_lru(lru);

	VM_BUG_ON(PageActive(page));
	VM_BUG_ON(PageUnevictable(page));
	VM_BUG_ON(PageLRU(page));

	SetPageLRU(page);
	if (active)
	SetPageActive(page);
	update_page_reclaim_stat(zone, page, file, active);
	add_page_to_lru_list(zone, 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, enum lru_list lru)
	{
	VM_BUG_ON(is_unevictable_lru(lru));

	pagevec_lru_move_fn(pvec, ____pagevec_lru_add_fn, (void *)lru);
	}

	EXPORT_SYMBOL(____pagevec_lru_add);

	/*
	* Try to drop buffers from the pages in a pagevec
	*/
	void pagevec_strip(struct pagevec *pvec)
	{
	int i;

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

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

	/**
	* pagevec_lookup - gang pagecache lookup
	* @pvec: Where the resulting pages are placed
	* @mapping: The address_space to search
	* @start: The starting page index
	* @nr_pages: The maximum number of pages
	*
	* pagevec_lookup() will search for and return a group of up to @nr_pages pages
	* in the mapping. 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.
	*
	* pagevec_lookup() returns the number of pages which were found.
	*/
	unsigned pagevec_lookup(struct pagevec pvec, struct address_space mapping,
	pgoff_t start, unsigned nr_pages)
	{
	pvec->nr = find_get_pages(mapping, start, nr_pages, pvec->pages);
	return pagevec_count(pvec);
	}

	EXPORT_SYMBOL(pagevec_lookup);

	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);

	#ifdef CONFIG_SWAP
	bdi_init(swapper_space.backing_dev_info);
	#endif

	/* 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
	*/
	}