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Version: 2.6.8   2.6.16   2.6.25   2.6.30   2.6.34  

Architecture: i386   arm   mips   ppc   alpha   m68k   sparc   sparc64  

   /*
    * mm/page-writeback.c.
    *
    * Copyright (C) 2002, Linus Torvalds.
    *
    * Contains functions related to writing back dirty pages at the
    * address_space level.
    *
    * 10Apr2002    akpm@zip.com.au
   *              Initial version
   */
  
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/spinlock.h>
  #include <linux/fs.h>
  #include <linux/mm.h>
  #include <linux/swap.h>
  #include <linux/slab.h>
  #include <linux/pagemap.h>
  #include <linux/writeback.h>
  #include <linux/init.h>
  #include <linux/backing-dev.h>
  #include <linux/blkdev.h>
  #include <linux/mpage.h>
  #include <linux/percpu.h>
  #include <linux/notifier.h>
  #include <linux/smp.h>
  #include <linux/sysctl.h>
  #include <linux/cpu.h>
  #include <linux/syscalls.h>
  
  /*
   * The maximum number of pages to writeout in a single bdflush/kupdate
   * operation.  We do this so we don't hold I_LOCK against an inode for
   * enormous amounts of time, which would block a userspace task which has
   * been forced to throttle against that inode.  Also, the code reevaluates
   * the dirty each time it has written this many pages.
   */
  #define MAX_WRITEBACK_PAGES     1024
  
  /*
   * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
   * will look to see if it needs to force writeback or throttling.
   */
  static long ratelimit_pages = 32;
  
  static long total_pages;        /* The total number of pages in the machine. */
  static int dirty_exceeded;      /* Dirty mem may be over limit */
  
  /*
   * When balance_dirty_pages decides that the caller needs to perform some
   * non-background writeback, this is how many pages it will attempt to write.
   * It should be somewhat larger than RATELIMIT_PAGES to ensure that reasonably
   * large amounts of I/O are submitted.
   */
  static inline long sync_writeback_pages(void)
  {
          return ratelimit_pages + ratelimit_pages / 2;
  }
  
  /* The following parameters are exported via /proc/sys/vm */
  
  /*
   * Start background writeback (via pdflush) at this percentage
   */
  int dirty_background_ratio = 10;
  
  /*
   * The generator of dirty data starts writeback at this percentage
   */
  int vm_dirty_ratio = 40;
  
  /*
   * The interval between `kupdate'-style writebacks, in centiseconds
   * (hundredths of a second)
   */
  int dirty_writeback_centisecs = 5 * 100;
  
  /*
   * The longest number of centiseconds for which data is allowed to remain dirty
   */
  int dirty_expire_centisecs = 30 * 100;
  
  /*
   * Flag that makes the machine dump writes/reads and block dirtyings.
   */
  int block_dump;
  
  /*
   * Flag that puts the machine in "laptop mode".
   */
  int laptop_mode;
  
  EXPORT_SYMBOL(laptop_mode);
  
  /* End of sysctl-exported parameters */
  
  
 static void background_writeout(unsigned long _min_pages);
 
 struct writeback_state
 {
         unsigned long nr_dirty;
         unsigned long nr_unstable;
         unsigned long nr_mapped;
         unsigned long nr_writeback;
 };
 
 static void get_writeback_state(struct writeback_state *wbs)
 {
         wbs->nr_dirty = read_page_state(nr_dirty);
         wbs->nr_unstable = read_page_state(nr_unstable);
         wbs->nr_mapped = read_page_state(nr_mapped);
         wbs->nr_writeback = read_page_state(nr_writeback);
 }
 
 /*
  * Work out the current dirty-memory clamping and background writeout
  * thresholds.
  *
  * The main aim here is to lower them aggressively if there is a lot of mapped
  * memory around.  To avoid stressing page reclaim with lots of unreclaimable
  * pages.  It is better to clamp down on writers than to start swapping, and
  * performing lots of scanning.
  *
  * We only allow 1/2 of the currently-unmapped memory to be dirtied.
  *
  * We don't permit the clamping level to fall below 5% - that is getting rather
  * excessive.
  *
  * We make sure that the background writeout level is below the adjusted
  * clamping level.
  */
 static void
 get_dirty_limits(struct writeback_state *wbs, long *pbackground, long *pdirty)
 {
         int background_ratio;           /* Percentages */
         int dirty_ratio;
         int unmapped_ratio;
         long background;
         long dirty;
         struct task_struct *tsk;
 
         get_writeback_state(wbs);
 
         unmapped_ratio = 100 - (wbs->nr_mapped * 100) / total_pages;
 
         dirty_ratio = vm_dirty_ratio;
         if (dirty_ratio > unmapped_ratio / 2)
                 dirty_ratio = unmapped_ratio / 2;
 
         if (dirty_ratio < 5)
                 dirty_ratio = 5;
 
         background_ratio = dirty_background_ratio;
         if (background_ratio >= dirty_ratio)
                 background_ratio = dirty_ratio / 2;
 
         background = (background_ratio * total_pages) / 100;
         dirty = (dirty_ratio * total_pages) / 100;
         tsk = current;
         if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
                 background += background / 4;
                 dirty += dirty / 4;
         }
         *pbackground = background;
         *pdirty = dirty;
 }
 
 /*
  * balance_dirty_pages() must be called by processes which are generating dirty
  * data.  It looks at the number of dirty pages in the machine and will force
  * the caller to perform writeback if the system is over `vm_dirty_ratio'.
  * If we're over `background_thresh' then pdflush is woken to perform some
  * writeout.
  */
 static void balance_dirty_pages(struct address_space *mapping)
 {
         struct writeback_state wbs;
         long nr_reclaimable;
         long background_thresh;
         long dirty_thresh;
         unsigned long pages_written = 0;
         unsigned long write_chunk = sync_writeback_pages();
 
         struct backing_dev_info *bdi = mapping->backing_dev_info;
 
         for (;;) {
                 struct writeback_control wbc = {
                         .bdi            = bdi,
                         .sync_mode      = WB_SYNC_NONE,
                         .older_than_this = NULL,
                         .nr_to_write    = write_chunk,
                 };
 
                 get_dirty_limits(&wbs, &background_thresh, &dirty_thresh);
                 nr_reclaimable = wbs.nr_dirty + wbs.nr_unstable;
                 if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
                         break;
 
                 dirty_exceeded = 1;
 
                 /* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
                  * Unstable writes are a feature of certain networked
                  * filesystems (i.e. NFS) in which data may have been
                  * written to the server's write cache, but has not yet
                  * been flushed to permanent storage.
                  */
                 if (nr_reclaimable) {
                         writeback_inodes(&wbc);
                         get_dirty_limits(&wbs, &background_thresh,
                                         &dirty_thresh);
                         nr_reclaimable = wbs.nr_dirty + wbs.nr_unstable;
                         if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
                                 break;
                         pages_written += write_chunk - wbc.nr_to_write;
                         if (pages_written >= write_chunk)
                                 break;          /* We've done our duty */
                 }
                 blk_congestion_wait(WRITE, HZ/10);
         }
 
         if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
                 dirty_exceeded = 0;
 
         if (writeback_in_progress(bdi))
                 return;         /* pdflush is already working this queue */
 
         /*
          * In laptop mode, we wait until hitting the higher threshold before
          * starting background writeout, and then write out all the way down
          * to the lower threshold.  So slow writers cause minimal disk activity.
          *
          * In normal mode, we start background writeout at the lower
          * background_thresh, to keep the amount of dirty memory low.
          */
         if ((laptop_mode && pages_written) ||
              (!laptop_mode && (nr_reclaimable > background_thresh)))
                 pdflush_operation(background_writeout, 0);
 }
 
 /**
  * balance_dirty_pages_ratelimited - balance dirty memory state
  * @mapping - address_space which was dirtied
  *
  * Processes which are dirtying memory should call in here once for each page
  * which was newly dirtied.  The function will periodically check the system's
  * dirty state and will initiate writeback if needed.
  *
  * On really big machines, get_writeback_state is expensive, so try to avoid
  * calling it too often (ratelimiting).  But once we're over the dirty memory
  * limit we decrease the ratelimiting by a lot, to prevent individual processes
  * from overshooting the limit by (ratelimit_pages) each.
  */
 void balance_dirty_pages_ratelimited(struct address_space *mapping)
 {
         static DEFINE_PER_CPU(int, ratelimits) = 0;
         long ratelimit;
 
         ratelimit = ratelimit_pages;
         if (dirty_exceeded)
                 ratelimit = 8;
 
         /*
          * Check the rate limiting. Also, we do not want to throttle real-time
          * tasks in balance_dirty_pages(). Period.
          */
         if (get_cpu_var(ratelimits)++ >= ratelimit) {
                 __get_cpu_var(ratelimits) = 0;
                 put_cpu_var(ratelimits);
                 balance_dirty_pages(mapping);
                 return;
         }
         put_cpu_var(ratelimits);
 }
 EXPORT_SYMBOL(balance_dirty_pages_ratelimited);
 
 /*
  * writeback at least _min_pages, and keep writing until the amount of dirty
  * memory is less than the background threshold, or until we're all clean.
  */
 static void background_writeout(unsigned long _min_pages)
 {
         long min_pages = _min_pages;
         struct writeback_control wbc = {
                 .bdi            = NULL,
                 .sync_mode      = WB_SYNC_NONE,
                 .older_than_this = NULL,
                 .nr_to_write    = 0,
                 .nonblocking    = 1,
         };
 
         for ( ; ; ) {
                 struct writeback_state wbs;
                 long background_thresh;
                 long dirty_thresh;
 
                 get_dirty_limits(&wbs, &background_thresh, &dirty_thresh);
                 if (wbs.nr_dirty + wbs.nr_unstable < background_thresh
                                 && min_pages <= 0)
                         break;
                 wbc.encountered_congestion = 0;
                 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
                 wbc.pages_skipped = 0;
                 writeback_inodes(&wbc);
                 min_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
                 if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
                         /* Wrote less than expected */
                         blk_congestion_wait(WRITE, HZ/10);
                         if (!wbc.encountered_congestion)
                                 break;
                 }
         }
 }
 
 /*
  * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
  * the whole world.  Returns 0 if a pdflush thread was dispatched.  Returns
  * -1 if all pdflush threads were busy.
  */
 int wakeup_bdflush(long nr_pages)
 {
         if (nr_pages == 0) {
                 struct writeback_state wbs;
 
                 get_writeback_state(&wbs);
                 nr_pages = wbs.nr_dirty + wbs.nr_unstable;
         }
         return pdflush_operation(background_writeout, nr_pages);
 }
 
 static void wb_timer_fn(unsigned long unused);
 static void laptop_timer_fn(unsigned long unused);
 
 static struct timer_list wb_timer =
                         TIMER_INITIALIZER(wb_timer_fn, 0, 0);
 static struct timer_list laptop_mode_wb_timer =
                         TIMER_INITIALIZER(laptop_timer_fn, 0, 0);
 
 /*
  * Periodic writeback of "old" data.
  *
  * Define "old": the first time one of an inode's pages is dirtied, we mark the
  * dirtying-time in the inode's address_space.  So this periodic writeback code
  * just walks the superblock inode list, writing back any inodes which are
  * older than a specific point in time.
  *
  * Try to run once per dirty_writeback_centisecs.  But if a writeback event
  * takes longer than a dirty_writeback_centisecs interval, then leave a
  * one-second gap.
  *
  * older_than_this takes precedence over nr_to_write.  So we'll only write back
  * all dirty pages if they are all attached to "old" mappings.
  */
 static void wb_kupdate(unsigned long arg)
 {
         unsigned long oldest_jif;
         unsigned long start_jif;
         unsigned long next_jif;
         long nr_to_write;
         struct writeback_state wbs;
         struct writeback_control wbc = {
                 .bdi            = NULL,
                 .sync_mode      = WB_SYNC_NONE,
                 .older_than_this = &oldest_jif,
                 .nr_to_write    = 0,
                 .nonblocking    = 1,
                 .for_kupdate    = 1,
         };
 
         sync_supers();
 
         get_writeback_state(&wbs);
         oldest_jif = jiffies - (dirty_expire_centisecs * HZ) / 100;
         start_jif = jiffies;
         next_jif = start_jif + (dirty_writeback_centisecs * HZ) / 100;
         nr_to_write = wbs.nr_dirty + wbs.nr_unstable +
                         (inodes_stat.nr_inodes - inodes_stat.nr_unused);
         while (nr_to_write > 0) {
                 wbc.encountered_congestion = 0;
                 wbc.nr_to_write = MAX_WRITEBACK_PAGES;
                 writeback_inodes(&wbc);
                 if (wbc.nr_to_write > 0) {
                         if (wbc.encountered_congestion)
                                 blk_congestion_wait(WRITE, HZ/10);
                         else
                                 break;  /* All the old data is written */
                 }
                 nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
         }
         if (time_before(next_jif, jiffies + HZ))
                 next_jif = jiffies + HZ;
         if (dirty_writeback_centisecs)
                 mod_timer(&wb_timer, next_jif);
 }
 
 /*
  * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
  */
 int dirty_writeback_centisecs_handler(ctl_table *table, int write,
                 struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
 {
         proc_dointvec(table, write, file, buffer, length, ppos);
         if (dirty_writeback_centisecs) {
                 mod_timer(&wb_timer,
                         jiffies + (dirty_writeback_centisecs * HZ) / 100);
         } else {
                 del_timer(&wb_timer);
         }
         return 0;
 }
 
 static void wb_timer_fn(unsigned long unused)
 {
         if (pdflush_operation(wb_kupdate, 0) < 0)
                 mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
 }
 
 static void laptop_flush(unsigned long unused)
 {
         sys_sync();
 }
 
 static void laptop_timer_fn(unsigned long unused)
 {
         pdflush_operation(laptop_flush, 0);
 }
 
 /*
  * We've spun up the disk and we're in laptop mode: schedule writeback
  * of all dirty data a few seconds from now.  If the flush is already scheduled
  * then push it back - the user is still using the disk.
  */
 void laptop_io_completion(void)
 {
         mod_timer(&laptop_mode_wb_timer, jiffies + laptop_mode * HZ);
 }
 
 /*
  * We're in laptop mode and we've just synced. The sync's writes will have
  * caused another writeback to be scheduled by laptop_io_completion.
  * Nothing needs to be written back anymore, so we unschedule the writeback.
  */
 void laptop_sync_completion(void)
 {
         del_timer(&laptop_mode_wb_timer);
 }
 
 /*
  * If ratelimit_pages is too high then we can get into dirty-data overload
  * if a large number of processes all perform writes at the same time.
  * If it is too low then SMP machines will call the (expensive)
  * get_writeback_state too often.
  *
  * Here we set ratelimit_pages to a level which ensures that when all CPUs are
  * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
  * thresholds before writeback cuts in.
  *
  * But the limit should not be set too high.  Because it also controls the
  * amount of memory which the balance_dirty_pages() caller has to write back.
  * If this is too large then the caller will block on the IO queue all the
  * time.  So limit it to four megabytes - the balance_dirty_pages() caller
  * will write six megabyte chunks, max.
  */
 
 static void set_ratelimit(void)
 {
         ratelimit_pages = total_pages / (num_online_cpus() * 32);
         if (ratelimit_pages < 16)
                 ratelimit_pages = 16;
         if (ratelimit_pages * PAGE_CACHE_SIZE > 4096 * 1024)
                 ratelimit_pages = (4096 * 1024) / PAGE_CACHE_SIZE;
 }
 
 static int
 ratelimit_handler(struct notifier_block *self, unsigned long u, void *v)
 {
         set_ratelimit();
         return 0;
 }
 
 static struct notifier_block ratelimit_nb = {
         .notifier_call  = ratelimit_handler,
         .next           = NULL,
 };
 
 /*
  * If the machine has a large highmem:lowmem ratio then scale back the default
  * dirty memory thresholds: allowing too much dirty highmem pins an excessive
  * number of buffer_heads.
  */
 void __init page_writeback_init(void)
 {
         long buffer_pages = nr_free_buffer_pages();
         long correction;
 
         total_pages = nr_free_pagecache_pages();
 
         correction = (100 * 4 * buffer_pages) / total_pages;
 
         if (correction < 100) {
                 dirty_background_ratio *= correction;
                 dirty_background_ratio /= 100;
                 vm_dirty_ratio *= correction;
                 vm_dirty_ratio /= 100;
         }
         mod_timer(&wb_timer, jiffies + (dirty_writeback_centisecs * HZ) / 100);
         set_ratelimit();
         register_cpu_notifier(&ratelimit_nb);
 }
 
 int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
 {
         if (wbc->nr_to_write <= 0)
                 return 0;
         if (mapping->a_ops->writepages)
                 return mapping->a_ops->writepages(mapping, wbc);
         return generic_writepages(mapping, wbc);
 }
 
 /**
  * write_one_page - write out a single page and optionally wait on I/O
  *
  * @page - the page to write
  * @wait - if true, wait on writeout
  *
  * The page must be locked by the caller and will be unlocked upon return.
  *
  * write_one_page() returns a negative error code if I/O failed.
  */
 int write_one_page(struct page *page, int wait)
 {
         struct address_space *mapping = page->mapping;
         int ret = 0;
         struct writeback_control wbc = {
                 .sync_mode = WB_SYNC_ALL,
                 .nr_to_write = 1,
         };
 
         BUG_ON(!PageLocked(page));
 
         if (wait)
                 wait_on_page_writeback(page);
 
         if (clear_page_dirty_for_io(page)) {
                 page_cache_get(page);
                 ret = mapping->a_ops->writepage(page, &wbc);
                 if (ret == 0 && wait) {
                         wait_on_page_writeback(page);
                         if (PageError(page))
                                 ret = -EIO;
                 }
                 page_cache_release(page);
         } else {
                 unlock_page(page);
         }
         return ret;
 }
 EXPORT_SYMBOL(write_one_page);
 
 /*
  * For address_spaces which do not use buffers.  Just tag the page as dirty in
  * its radix tree.
  *
  * This is also used when a single buffer is being dirtied: we want to set the
  * page dirty in that case, but not all the buffers.  This is a "bottom-up"
  * dirtying, whereas __set_page_dirty_buffers() is a "top-down" dirtying.
  *
  * Most callers have locked the page, which pins the address_space in memory.
  * But zap_pte_range() does not lock the page, however in that case the
  * mapping is pinned by the vma's ->vm_file reference.
  *
  * We take care to handle the case where the page was truncated from the
  * mapping by re-checking page_mapping() insode tree_lock.
  */
 int __set_page_dirty_nobuffers(struct page *page)
 {
         int ret = 0;
 
         if (!TestSetPageDirty(page)) {
                 struct address_space *mapping = page_mapping(page);
 
                 if (mapping) {
                         spin_lock_irq(&mapping->tree_lock);
                         mapping = page_mapping(page);
                         if (page_mapping(page)) { /* Race with truncate? */
                                 BUG_ON(page_mapping(page) != mapping);
                                 if (!mapping->backing_dev_info->memory_backed)
                                         inc_page_state(nr_dirty);
                                 radix_tree_tag_set(&mapping->page_tree,
                                         page_index(page), PAGECACHE_TAG_DIRTY);
                         }
                         spin_unlock_irq(&mapping->tree_lock);
                         if (mapping->host) {
                                 /* !PageAnon && !swapper_space */
                                 __mark_inode_dirty(mapping->host,
                                                         I_DIRTY_PAGES);
                         }
                 }
         }
         return ret;
 }
 EXPORT_SYMBOL(__set_page_dirty_nobuffers);
 
 /*
  * When a writepage implementation decides that it doesn't want to write this
  * page for some reason, it should redirty the locked page via
  * redirty_page_for_writepage() and it should then unlock the page and return 0
  */
 int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page)
 {
         wbc->pages_skipped++;
         return __set_page_dirty_nobuffers(page);
 }
 EXPORT_SYMBOL(redirty_page_for_writepage);
 
 /*
  * If the mapping doesn't provide a set_page_dirty a_op, then
  * just fall through and assume that it wants buffer_heads.
  */
 int fastcall set_page_dirty(struct page *page)
 {
         struct address_space *mapping = page_mapping(page);
 
         if (likely(mapping)) {
                 int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
                 if (spd)
                         return (*spd)(page);
                 return __set_page_dirty_buffers(page);
         }
         if (!PageDirty(page))
                 SetPageDirty(page);
         return 0;
 }
 EXPORT_SYMBOL(set_page_dirty);
 
 /*
  * set_page_dirty() is racy if the caller has no reference against
  * page->mapping->host, and if the page is unlocked.  This is because another
  * CPU could truncate the page off the mapping and then free the mapping.
  *
  * Usually, the page _is_ locked, or the caller is a user-space process which
  * holds a reference on the inode by having an open file.
  *
  * In other cases, the page should be locked before running set_page_dirty().
  */
 int set_page_dirty_lock(struct page *page)
 {
         int ret;
 
         lock_page(page);
         ret = set_page_dirty(page);
         unlock_page(page);
         return ret;
 }
 EXPORT_SYMBOL(set_page_dirty_lock);
 
 /*
  * Clear a page's dirty flag, while caring for dirty memory accounting. 
  * Returns true if the page was previously dirty.
  */
 int test_clear_page_dirty(struct page *page)
 {
         struct address_space *mapping = page_mapping(page);
         unsigned long flags;
 
         if (mapping) {
                 spin_lock_irqsave(&mapping->tree_lock, flags);
                 if (TestClearPageDirty(page)) {
                         radix_tree_tag_clear(&mapping->page_tree,
                                                 page_index(page),
                                                 PAGECACHE_TAG_DIRTY);
                         spin_unlock_irqrestore(&mapping->tree_lock, flags);
                         if (!mapping->backing_dev_info->memory_backed)
                                 dec_page_state(nr_dirty);
                         return 1;
                 }
                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
                 return 0;
         }
         return TestClearPageDirty(page);
 }
 EXPORT_SYMBOL(test_clear_page_dirty);
 
 /*
  * Clear a page's dirty flag, while caring for dirty memory accounting.
  * Returns true if the page was previously dirty.
  *
  * This is for preparing to put the page under writeout.  We leave the page
  * tagged as dirty in the radix tree so that a concurrent write-for-sync
  * can discover it via a PAGECACHE_TAG_DIRTY walk.  The ->writepage
  * implementation will run either set_page_writeback() or set_page_dirty(),
  * at which stage we bring the page's dirty flag and radix-tree dirty tag
  * back into sync.
  *
  * This incoherency between the page's dirty flag and radix-tree tag is
  * unfortunate, but it only exists while the page is locked.
  */
 int clear_page_dirty_for_io(struct page *page)
 {
         struct address_space *mapping = page_mapping(page);
 
         if (mapping) {
                 if (TestClearPageDirty(page)) {
                         if (!mapping->backing_dev_info->memory_backed)
                                 dec_page_state(nr_dirty);
                         return 1;
                 }
                 return 0;
         }
         return TestClearPageDirty(page);
 }
 EXPORT_SYMBOL(clear_page_dirty_for_io);
 
 /*
  * Clear a page's dirty flag while ignoring dirty memory accounting
  */
 int __clear_page_dirty(struct page *page)
 {
         struct address_space *mapping = page_mapping(page);
 
         if (mapping) {
                 unsigned long flags;
 
                 spin_lock_irqsave(&mapping->tree_lock, flags);
                 if (TestClearPageDirty(page)) {
                         radix_tree_tag_clear(&mapping->page_tree,
                                                 page_index(page),
                                                 PAGECACHE_TAG_DIRTY);
                         spin_unlock_irqrestore(&mapping->tree_lock, flags);
                         return 1;
                 }
                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
                 return 0;
         }
         return TestClearPageDirty(page);
 }
 
 int test_clear_page_writeback(struct page *page)
 {
         struct address_space *mapping = page_mapping(page);
         int ret;
 
         if (mapping) {
                 unsigned long flags;
 
                 spin_lock_irqsave(&mapping->tree_lock, flags);
                 ret = TestClearPageWriteback(page);
                 if (ret)
                         radix_tree_tag_clear(&mapping->page_tree,
                                                 page_index(page),
                                                 PAGECACHE_TAG_WRITEBACK);
                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
         } else {
                 ret = TestClearPageWriteback(page);
         }
         return ret;
 }
 
 int test_set_page_writeback(struct page *page)
 {
         struct address_space *mapping = page_mapping(page);
         int ret;
 
         if (mapping) {
                 unsigned long flags;
 
                 spin_lock_irqsave(&mapping->tree_lock, flags);
                 ret = TestSetPageWriteback(page);
                 if (!ret)
                         radix_tree_tag_set(&mapping->page_tree,
                                                 page_index(page),
                                                 PAGECACHE_TAG_WRITEBACK);
                 if (!PageDirty(page))
                         radix_tree_tag_clear(&mapping->page_tree,
                                                 page_index(page),
                                                 PAGECACHE_TAG_DIRTY);
                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
         } else {
                 ret = TestSetPageWriteback(page);
         }
         return ret;
 
 }
 EXPORT_SYMBOL(test_set_page_writeback);
 
 /*
  * Return true if any of the pages in the mapping are marged with the
  * passed tag.
  */
 int mapping_tagged(struct address_space *mapping, int tag)
 {
         unsigned long flags;
         int ret;
 
         spin_lock_irqsave(&mapping->tree_lock, flags);
         ret = radix_tree_tagged(&mapping->page_tree, tag);
         spin_unlock_irqrestore(&mapping->tree_lock, flags);
         return ret;
 }
 EXPORT_SYMBOL(mapping_tagged);
 

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