FreeBSD/Linux Kernel Cross Reference
sys/mm/swap.c

     /*
      *  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/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)) {
                    struct zone *zone = page_zone(page);
                    struct lruvec *lruvec;
                    unsigned long flags;
    
                    spin_lock_irqsave(&zone->lru_lock, flags);
                    lruvec = mem_cgroup_page_lruvec(page, zone);
                    VM_BUG_ON(!PageLRU(page));
                    __ClearPageLRU(page);
                    del_page_from_lru_list(page, lruvec, page_off_lru(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;
    
                            /*
                             * THP can not break up slab pages so avoid taking
                             * compound_lock().  Slab performs non-atomic bit ops
                             * on page->flags for better performance.  In particular
                             * slab_unlock() in slub used to be a hot path.  It is
                             * still hot on arches that do not support
                             * this_cpu_cmpxchg_double().
                             */
                            if (PageSlab(page_head)) {
                                    if (PageTail(page)) {
                                            if (put_page_testzero(page_head))
                                                    VM_BUG_ON(1);
   
                                           atomic_dec(&page->_mapcount);
                                           goto skip_lock_tail;
                                   } else
                                           goto skip_lock;
                           }
                           /*
                            * 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);
   skip_lock:
                                   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);
   
   skip_lock_tail:
                           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))) {
   
                   /* Ref to put_compound_page() comment. */
                   if (PageSlab(page_head)) {
                           if (likely(PageTail(page))) {
                                   __get_page_tail_foll(page, false);
                                   return true;
                           } else {
                                   put_page(page_head);
                                   return false;
                           }
                   }
   
                   /*
                    * 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);
   
   /*
    * 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);
                   page_cache_get(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 zone *zone = NULL;
           struct lruvec *lruvec;
           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);
                   }
   
                   lruvec = mem_cgroup_page_lruvec(page, zone);
                   (*move_fn)(page, lruvec, 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, struct lruvec *lruvec,
                                    void *arg)
   {
           int *pgmoved = arg;
   
           if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
                   enum lru_list lru = page_lru_base_type(page);
                   list_move_tail(&page->lru, &lruvec->lists[lru]);
                   (*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 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);
   
                   __count_vm_event(PGACTIVATE);
                   update_page_reclaim_stat(lruvec, 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, mem_cgroup_page_lruvec(page, zone), 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);
   
   /*
    * Order of operations is important: flush the pagevec when it's already
    * full, not when adding the last page, to make sure that last page is
    * not added to the LRU directly when passed to this function. Because
    * mark_page_accessed() (called after this when writing) only activates
    * pages that are on the LRU, linear writes in subpage chunks would see
    * every PAGEVEC_SIZE page activated, which is unexpected.
    */
   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_space(pvec))
                   __pagevec_lru_add(pvec, lru);
           pagevec_add(pvec, page);
           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);
           struct lruvec *lruvec;
   
           spin_lock_irq(&zone->lru_lock);
           lruvec = mem_cgroup_page_lruvec(page, zone);
           SetPageUnevictable(page);
           SetPageLRU(page);
           add_page_to_lru_list(page, lruvec, 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, 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);
   }
   
   /*
    * 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 *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)
   {
           lru_add_drain_cpu(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;
           LIST_HEAD(pages_to_free);
           struct zone *zone = NULL;
           struct lruvec *lruvec;
           unsigned long uninitialized_var(flags);
   
           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);
                           }
   
                           lruvec = mem_cgroup_page_lruvec(page, zone);
                           VM_BUG_ON(!PageLRU(page));
                           __ClearPageLRU(page);
                           del_page_from_lru_list(page, lruvec, page_off_lru(page));
                   }
   
                   list_add(&page->lru, &pages_to_free);
           }
           if (zone)
                   spin_unlock_irqrestore(&zone->lru_lock, flags);
   
           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)
   {
           int uninitialized_var(active);
           enum lru_list lru;
           const int file = 0;
   
           VM_BUG_ON(!PageHead(page));
           VM_BUG_ON(PageCompound(page_tail));
           VM_BUG_ON(PageLRU(page_tail));
           VM_BUG_ON(NR_CPUS != 1 &&
                     !spin_is_locked(&lruvec_zone(lruvec)->lru_lock));
   
           SetPageLRU(page_tail);
   
           if (page_evictable(page_tail)) {
                   if (PageActive(page)) {
                           SetPageActive(page_tail);
                           active = 1;
                           lru = LRU_ACTIVE_ANON;
                   } else {
                           active = 0;
                           lru = LRU_INACTIVE_ANON;
                   }
           } else {
                   SetPageUnevictable(page_tail);
                   lru = LRU_UNEVICTABLE;
           }
   
           if (likely(PageLRU(page)))
                   list_add_tail(&page_tail->lru, &page->lru);
           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, lru);
                   list_head = page_tail->lru.prev;
                   list_move_tail(&page_tail->lru, list_head);
           }
   
           if (!PageUnevictable(page))
                   update_page_reclaim_stat(lruvec, file, active);
   }
   #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
   
   static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
                                    void *arg)
   {
           enum lru_list lru = (enum lru_list)arg;
           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);
           add_page_to_lru_list(page, lruvec, lru);
           update_page_reclaim_stat(lruvec, file, active);
   }
   
   /*
    * 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);
   
   /**
    * 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
            */
   }

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