/*
   *  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);

  /**
   * put_pages_list(): release a list of pages
   *
   * Release a list of pages which are strung together on page.lru.  Currently
   * used by read_cache_pages() and related error recovery code.
   *
   * @pages: list of pages threaded on page->lru
   */
  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);

  /*
   * 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_move_tail(&page->lru, &zone->inactive_list);

  		__count_vm_event(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);

  		__count_vm_event(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)
  {

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

  		spin_lock_irqsave(&zone->lru_lock, flags);

  		BUG_ON(!PageLRU(page));

  		__ClearPageLRU(page);

  		del_page_from_lru(zone, page);

  		spin_unlock_irqrestore(&zone->lru_lock, flags);
  	}
  	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];

  		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;

  		if (PageLRU(page)) {
  			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);
  			}

  			BUG_ON(!PageLRU(page));

  			__ClearPageLRU(page);

  			del_page_from_lru(zone, page);

  		}
  
  		if (!pagevec_add(&pages_to_free, page)) {
  			if (zone) {

  				spin_unlock_irq(&zone->lru_lock);

  				zone = NULL;

  			}

  			__pagevec_free(&pages_to_free);
  			pagevec_reinit(&pages_to_free);
    		}

  	}
  	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);
  		}

  		BUG_ON(PageLRU(page));
  		SetPageLRU(page);

  		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);
  		}

  		BUG_ON(PageLRU(page));
  		SetPageLRU(page);

  		BUG_ON(PageActive(page));
  		SetPageActive(page);

  		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)) {

  			if (PagePrivate(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 */

  /*
   * 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);
  }