mm/swap.c - kernel/msm-4.19 - Gitiles

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

 /*
  * This file contains the default values for the opereation 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/module.h>
 #include <linux/percpu_counter.h>
 #include <linux/percpu.h>
 #include <linux/cpu.h>
 #include <linux/notifier.h>
 #include <linux/init.h>

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

 static void put_compound_page(struct page *page)
 {
 	page = (struct page *)page_private(page);
 	if (put_page_testzero(page)) {
 		void (*dtor)(struct page *page);

 		dtor = (void (*)(struct page *))page[1].lru.next;
 		(*dtor)(page);
 	}
 }

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

 /*
  * 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.  The page still has PageWriteback set, which will pin it.
  *
  * We don't expect many pages to come through here, so don't bother batching
  * things up.
  *
  * To avoid placing the page at the tail of the LRU while PG_writeback is still
  * set, this function will clear PG_writeback before performing the page
  * motion.  Do that inside the lru lock because once PG_writeback is cleared
  * we may not touch the page.
  *
  * Returns zero if it cleared PG_writeback.
  */
 int rotate_reclaimable_page(struct page *page)
 {
 	struct zone *zone;
 	unsigned long flags;

 	if (PageLocked(page))
 		return 1;
 	if (PageDirty(page))
 		return 1;
 	if (PageActive(page))
 		return 1;
 	if (!PageLRU(page))
 		return 1;

 	zone = page_zone(page);
 	spin_lock_irqsave(&zone->lru_lock, flags);
 	if (PageLRU(page) && !PageActive(page)) {
 		list_del(&page->lru);
 		list_add_tail(&page->lru, &zone->inactive_list);
 		inc_page_state(pgrotated);
 	}
 	if (!test_clear_page_writeback(page))
 		BUG();
 	spin_unlock_irqrestore(&zone->lru_lock, flags);
 	return 0;
 }

 /*
  * FIXME: speed this up?
  */
 void fastcall activate_page(struct page *page)
 {
 	struct zone *zone = page_zone(page);

 	spin_lock_irq(&zone->lru_lock);
 	if (PageLRU(page) && !PageActive(page)) {
 		del_page_from_inactive_list(zone, page);
 		SetPageActive(page);
 		add_page_to_active_list(zone, page);
 		inc_page_state(pgactivate);
 	}
 	spin_unlock_irq(&zone->lru_lock);
 }

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

 EXPORT_SYMBOL(mark_page_accessed);

 /**
  * lru_cache_add: add a page to the page lists
  * @page: the page to add
  */
 static DEFINE_PER_CPU(struct pagevec, lru_add_pvecs) = { 0, };
 static DEFINE_PER_CPU(struct pagevec, lru_add_active_pvecs) = { 0, };

 void fastcall lru_cache_add(struct page *page)
 {
 	struct pagevec *pvec = &get_cpu_var(lru_add_pvecs);

 	page_cache_get(page);
 	if (!pagevec_add(pvec, page))
 		__pagevec_lru_add(pvec);
 	put_cpu_var(lru_add_pvecs);
 }

 void fastcall lru_cache_add_active(struct page *page)
 {
 	struct pagevec *pvec = &get_cpu_var(lru_add_active_pvecs);

 	page_cache_get(page);
 	if (!pagevec_add(pvec, page))
 		__pagevec_lru_add_active(pvec);
 	put_cpu_var(lru_add_active_pvecs);
 }

 static void __lru_add_drain(int cpu)
 {
 	struct pagevec *pvec = &per_cpu(lru_add_pvecs, cpu);

 	/* CPU is dead, so no locking needed. */
 	if (pagevec_count(pvec))
 		__pagevec_lru_add(pvec);
 	pvec = &per_cpu(lru_add_active_pvecs, cpu);
 	if (pagevec_count(pvec))
 		__pagevec_lru_add_active(pvec);
 }

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

 #ifdef CONFIG_NUMA
 static void lru_add_drain_per_cpu(void *dummy)
 {
 	lru_add_drain();
 }

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

 #else

 /*
  * Returns 0 for success
  */
 int lru_add_drain_all(void)
 {
 	lru_add_drain();
 	return 0;
 }
 #endif

 /*
  * This path almost never happens for VM activity - pages are normally
  * freed via pagevecs.  But it gets used by networking.
  */
 void fastcall __page_cache_release(struct page *page)
 {
 	unsigned long flags;
 	struct zone *zone = page_zone(page);

 	spin_lock_irqsave(&zone->lru_lock, flags);
 	if (TestClearPageLRU(page))
 		del_page_from_lru(zone, page);
 	if (page_count(page) != 0)
 		page = NULL;
 	spin_unlock_irqrestore(&zone->lru_lock, flags);
 	if (page)
 		free_hot_page(page);
 }

 EXPORT_SYMBOL(__page_cache_release);

 /*
  * 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_cache(): we recheck the
  * page count inside the lock to see whether shrink_cache grabbed the page
  * via the LRU.  If it did, give up: shrink_cache will free it.
  */
 void release_pages(struct page **pages, int nr, int cold)
 {
 	int i;
 	struct pagevec pages_to_free;
 	struct zone *zone = NULL;

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

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

 		if (!put_page_testzero(page))
 			continue;

 		pagezone = page_zone(page);
 		if (pagezone != zone) {
 			if (zone)
 				spin_unlock_irq(&zone->lru_lock);
 			zone = pagezone;
 			spin_lock_irq(&zone->lru_lock);
 		}
 		if (TestClearPageLRU(page))
 			del_page_from_lru(zone, page);
 		if (page_count(page) == 0) {
 			if (!pagevec_add(&pages_to_free, page)) {
 				spin_unlock_irq(&zone->lru_lock);
 				__pagevec_free(&pages_to_free);
 				pagevec_reinit(&pages_to_free);
 				zone = NULL;	/* No lock is held */
 			}
 		}
 	}
 	if (zone)
 		spin_unlock_irq(&zone->lru_lock);

 	pagevec_free(&pages_to_free);
 }

 /*
  * 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);

 /*
  * pagevec_release() for pages which are known to not be on the LRU
  *
  * This function reinitialises the caller's pagevec.
  */
 void __pagevec_release_nonlru(struct pagevec *pvec)
 {
 	int i;
 	struct pagevec pages_to_free;

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

 		BUG_ON(PageLRU(page));
 		if (put_page_testzero(page))
 			pagevec_add(&pages_to_free, page);
 	}
 	pagevec_free(&pages_to_free);
 	pagevec_reinit(pvec);
 }

 /*
  * 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)
 {
 	int i;
 	struct zone *zone = NULL;

 	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_irq(&zone->lru_lock);
 			zone = pagezone;
 			spin_lock_irq(&zone->lru_lock);
 		}
 		if (TestSetPageLRU(page))
 			BUG();
 		add_page_to_inactive_list(zone, page);
 	}
 	if (zone)
 		spin_unlock_irq(&zone->lru_lock);
 	release_pages(pvec->pages, pvec->nr, pvec->cold);
 	pagevec_reinit(pvec);
 }

 EXPORT_SYMBOL(__pagevec_lru_add);

 void __pagevec_lru_add_active(struct pagevec *pvec)
 {
 	int i;
 	struct zone *zone = NULL;

 	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_irq(&zone->lru_lock);
 			zone = pagezone;
 			spin_lock_irq(&zone->lru_lock);
 		}
 		if (TestSetPageLRU(page))
 			BUG();
 		if (TestSetPageActive(page))
 			BUG();
 		add_page_to_active_list(zone, page);
 	}
 	if (zone)
 		spin_unlock_irq(&zone->lru_lock);
 	release_pages(pvec->pages, pvec->nr, pvec->cold);
 	pagevec_reinit(pvec);
 }

 /*
  * 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 (PagePrivate(page) && !TestSetPageLocked(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);

 #ifdef CONFIG_SMP
 /*
  * We tolerate a little inaccuracy to avoid ping-ponging the counter between
  * CPUs
  */
 #define ACCT_THRESHOLD	max(16, NR_CPUS * 2)

 static DEFINE_PER_CPU(long, committed_space) = 0;

 void vm_acct_memory(long pages)
 {
 	long *local;

 	preempt_disable();
 	local = &__get_cpu_var(committed_space);
 	*local += pages;
 	if (*local > ACCT_THRESHOLD || *local < -ACCT_THRESHOLD) {
 		atomic_add(*local, &vm_committed_space);
 		*local = 0;
 	}
 	preempt_enable();
 }

 #ifdef CONFIG_HOTPLUG_CPU

 /* Drop the CPU's cached committed space back into the central pool. */
 static int cpu_swap_callback(struct notifier_block *nfb,
 			     unsigned long action,
 			     void *hcpu)
 {
 	long *committed;

 	committed = &per_cpu(committed_space, (long)hcpu);
 	if (action == CPU_DEAD) {
 		atomic_add(*committed, &vm_committed_space);
 		*committed = 0;
 		__lru_add_drain((long)hcpu);
 	}
 	return NOTIFY_OK;
 }
 #endif /* CONFIG_HOTPLUG_CPU */
 #endif /* CONFIG_SMP */

 #ifdef CONFIG_SMP
 void percpu_counter_mod(struct percpu_counter *fbc, long amount)
 {
 	long count;
 	long *pcount;
 	int cpu = get_cpu();

 	pcount = per_cpu_ptr(fbc->counters, cpu);
 	count = *pcount + amount;
 	if (count >= FBC_BATCH || count <= -FBC_BATCH) {
 		spin_lock(&fbc->lock);
 		fbc->count += count;
 		*pcount = 0;
 		spin_unlock(&fbc->lock);
 	} else {
 		*pcount = count;
 	}
 	put_cpu();
 }
 EXPORT_SYMBOL(percpu_counter_mod);

 /*
  * Add up all the per-cpu counts, return the result.  This is a more accurate
  * but much slower version of percpu_counter_read_positive()
  */
 long percpu_counter_sum(struct percpu_counter *fbc)
 {
 	long ret;
 	int cpu;

 	spin_lock(&fbc->lock);
 	ret = fbc->count;
 	for_each_cpu(cpu) {
 		long *pcount = per_cpu_ptr(fbc->counters, cpu);
 		ret += *pcount;
 	}
 	spin_unlock(&fbc->lock);
 	return ret < 0 ? 0 : ret;
 }
 EXPORT_SYMBOL(percpu_counter_sum);
 #endif

 /*
  * Perform any setup for the swap system
  */
 void __init swap_setup(void)
 {
 	unsigned long megs = num_physpages >> (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
 	 */
 	hotcpu_notifier(cpu_swap_callback, 0);
 }
	/*
	* linux/mm/swap.c
	*
	* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
	*/

	/*
	* This file contains the default values for the opereation 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/module.h>
	#include <linux/percpu_counter.h>
	#include <linux/percpu.h>
	#include <linux/cpu.h>
	#include <linux/notifier.h>
	#include <linux/init.h>

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

	static void put_compound_page(struct page *page)
	{
	page = (struct page *)page_private(page);
	if (put_page_testzero(page)) {
	void (dtor)(struct page page);

	dtor = (void ()(struct page ))page[1].lru.next;
	(*dtor)(page);
	}
	}

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

	/*
	* 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. The page still has PageWriteback set, which will pin it.
	*
	* We don't expect many pages to come through here, so don't bother batching
	* things up.
	*
	* To avoid placing the page at the tail of the LRU while PG_writeback is still
	* set, this function will clear PG_writeback before performing the page
	* motion. Do that inside the lru lock because once PG_writeback is cleared
	* we may not touch the page.
	*
	* Returns zero if it cleared PG_writeback.
	*/
	int rotate_reclaimable_page(struct page *page)
	{
	struct zone *zone;
	unsigned long flags;

	if (PageLocked(page))
	return 1;
	if (PageDirty(page))
	return 1;
	if (PageActive(page))
	return 1;
	if (!PageLRU(page))
	return 1;

	zone = page_zone(page);
	spin_lock_irqsave(&zone->lru_lock, flags);
	if (PageLRU(page) && !PageActive(page)) {
	list_del(&page->lru);
	list_add_tail(&page->lru, &zone->inactive_list);
	inc_page_state(pgrotated);
	}
	if (!test_clear_page_writeback(page))
	BUG();
	spin_unlock_irqrestore(&zone->lru_lock, flags);
	return 0;
	}

	/*
	* FIXME: speed this up?
	*/
	void fastcall activate_page(struct page *page)
	{
	struct zone *zone = page_zone(page);

	spin_lock_irq(&zone->lru_lock);
	if (PageLRU(page) && !PageActive(page)) {
	del_page_from_inactive_list(zone, page);
	SetPageActive(page);
	add_page_to_active_list(zone, page);
	inc_page_state(pgactivate);
	}
	spin_unlock_irq(&zone->lru_lock);
	}

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

	EXPORT_SYMBOL(mark_page_accessed);

	/**
	* lru_cache_add: add a page to the page lists
	* @page: the page to add
	*/
	static DEFINE_PER_CPU(struct pagevec, lru_add_pvecs) = { 0, };
	static DEFINE_PER_CPU(struct pagevec, lru_add_active_pvecs) = { 0, };

	void fastcall lru_cache_add(struct page *page)
	{
	struct pagevec *pvec = &get_cpu_var(lru_add_pvecs);

	page_cache_get(page);
	if (!pagevec_add(pvec, page))
	__pagevec_lru_add(pvec);
	put_cpu_var(lru_add_pvecs);
	}

	void fastcall lru_cache_add_active(struct page *page)
	{
	struct pagevec *pvec = &get_cpu_var(lru_add_active_pvecs);

	page_cache_get(page);
	if (!pagevec_add(pvec, page))
	__pagevec_lru_add_active(pvec);
	put_cpu_var(lru_add_active_pvecs);
	}

	static void __lru_add_drain(int cpu)
	{
	struct pagevec *pvec = &per_cpu(lru_add_pvecs, cpu);

	/* CPU is dead, so no locking needed. */
	if (pagevec_count(pvec))
	__pagevec_lru_add(pvec);
	pvec = &per_cpu(lru_add_active_pvecs, cpu);
	if (pagevec_count(pvec))
	__pagevec_lru_add_active(pvec);
	}

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

	#ifdef CONFIG_NUMA
	static void lru_add_drain_per_cpu(void *dummy)
	{
	lru_add_drain();
	}

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

	#else

	/*
	* Returns 0 for success
	*/
	int lru_add_drain_all(void)
	{
	lru_add_drain();
	return 0;
	}
	#endif

	/*
	* This path almost never happens for VM activity - pages are normally
	* freed via pagevecs. But it gets used by networking.
	*/
	void fastcall __page_cache_release(struct page *page)
	{
	unsigned long flags;
	struct zone *zone = page_zone(page);

	spin_lock_irqsave(&zone->lru_lock, flags);
	if (TestClearPageLRU(page))
	del_page_from_lru(zone, page);
	if (page_count(page) != 0)
	page = NULL;
	spin_unlock_irqrestore(&zone->lru_lock, flags);
	if (page)
	free_hot_page(page);
	}

	EXPORT_SYMBOL(__page_cache_release);

	/*
	* 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_cache(): we recheck the
	* page count inside the lock to see whether shrink_cache grabbed the page
	* via the LRU. If it did, give up: shrink_cache will free it.
	*/
	void release_pages(struct page **pages, int nr, int cold)
	{
	int i;
	struct pagevec pages_to_free;
	struct zone *zone = NULL;

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

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

	if (!put_page_testzero(page))
	continue;

	pagezone = page_zone(page);
	if (pagezone != zone) {
	if (zone)
	spin_unlock_irq(&zone->lru_lock);
	zone = pagezone;
	spin_lock_irq(&zone->lru_lock);
	}
	if (TestClearPageLRU(page))
	del_page_from_lru(zone, page);
	if (page_count(page) == 0) {
	if (!pagevec_add(&pages_to_free, page)) {
	spin_unlock_irq(&zone->lru_lock);
	__pagevec_free(&pages_to_free);
	pagevec_reinit(&pages_to_free);
	zone = NULL; /* No lock is held */
	}
	}
	}
	if (zone)
	spin_unlock_irq(&zone->lru_lock);

	pagevec_free(&pages_to_free);
	}

	/*
	* 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);

	/*
	* pagevec_release() for pages which are known to not be on the LRU
	*
	* This function reinitialises the caller's pagevec.
	*/
	void __pagevec_release_nonlru(struct pagevec *pvec)
	{
	int i;
	struct pagevec pages_to_free;

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

	BUG_ON(PageLRU(page));
	if (put_page_testzero(page))
	pagevec_add(&pages_to_free, page);
	}
	pagevec_free(&pages_to_free);
	pagevec_reinit(pvec);
	}

	/*
	* 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)
	{
	int i;
	struct zone *zone = NULL;

	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_irq(&zone->lru_lock);
	zone = pagezone;
	spin_lock_irq(&zone->lru_lock);
	}
	if (TestSetPageLRU(page))
	BUG();
	add_page_to_inactive_list(zone, page);
	}
	if (zone)
	spin_unlock_irq(&zone->lru_lock);
	release_pages(pvec->pages, pvec->nr, pvec->cold);
	pagevec_reinit(pvec);
	}

	EXPORT_SYMBOL(__pagevec_lru_add);

	void __pagevec_lru_add_active(struct pagevec *pvec)
	{
	int i;
	struct zone *zone = NULL;

	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_irq(&zone->lru_lock);
	zone = pagezone;
	spin_lock_irq(&zone->lru_lock);
	}
	if (TestSetPageLRU(page))
	BUG();
	if (TestSetPageActive(page))
	BUG();
	add_page_to_active_list(zone, page);
	}
	if (zone)
	spin_unlock_irq(&zone->lru_lock);
	release_pages(pvec->pages, pvec->nr, pvec->cold);
	pagevec_reinit(pvec);
	}

	/*
	* 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 (PagePrivate(page) && !TestSetPageLocked(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);

	#ifdef CONFIG_SMP
	/*
	* We tolerate a little inaccuracy to avoid ping-ponging the counter between
	* CPUs
	*/
	#define ACCT_THRESHOLD max(16, NR_CPUS * 2)

	static DEFINE_PER_CPU(long, committed_space) = 0;

	void vm_acct_memory(long pages)
	{
	long *local;

	preempt_disable();
	local = &__get_cpu_var(committed_space);
	*local += pages;
	if (local > ACCT_THRESHOLD \|\| local < -ACCT_THRESHOLD) {
	atomic_add(*local, &vm_committed_space);
	*local = 0;
	}
	preempt_enable();
	}

	#ifdef CONFIG_HOTPLUG_CPU

	/* Drop the CPU's cached committed space back into the central pool. */
	static int cpu_swap_callback(struct notifier_block *nfb,
	unsigned long action,
	void *hcpu)
	{
	long *committed;

	committed = &per_cpu(committed_space, (long)hcpu);
	if (action == CPU_DEAD) {
	atomic_add(*committed, &vm_committed_space);
	*committed = 0;
	__lru_add_drain((long)hcpu);
	}
	return NOTIFY_OK;
	}
	#endif /* CONFIG_HOTPLUG_CPU */
	#endif /* CONFIG_SMP */

	#ifdef CONFIG_SMP
	void percpu_counter_mod(struct percpu_counter *fbc, long amount)
	{
	long count;
	long *pcount;
	int cpu = get_cpu();

	pcount = per_cpu_ptr(fbc->counters, cpu);
	count = *pcount + amount;
	if (count >= FBC_BATCH \|\| count <= -FBC_BATCH) {
	spin_lock(&fbc->lock);
	fbc->count += count;
	*pcount = 0;
	spin_unlock(&fbc->lock);
	} else {
	*pcount = count;
	}
	put_cpu();
	}
	EXPORT_SYMBOL(percpu_counter_mod);

	/*
	* Add up all the per-cpu counts, return the result. This is a more accurate
	* but much slower version of percpu_counter_read_positive()
	*/
	long percpu_counter_sum(struct percpu_counter *fbc)
	{
	long ret;
	int cpu;

	spin_lock(&fbc->lock);
	ret = fbc->count;
	for_each_cpu(cpu) {
	long *pcount = per_cpu_ptr(fbc->counters, cpu);
	ret += *pcount;
	}
	spin_unlock(&fbc->lock);
	return ret < 0 ? 0 : ret;
	}
	EXPORT_SYMBOL(percpu_counter_sum);
	#endif

	/*
	* Perform any setup for the swap system
	*/
	void __init swap_setup(void)
	{
	unsigned long megs = num_physpages >> (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
	*/
	hotcpu_notifier(cpu_swap_callback, 0);
	}