#include <linux/wait.h>
  #include <linux/backing-dev.h>

  #include <linux/kthread.h>
  #include <linux/freezer.h>

  #include <linux/fs.h>

  #include <linux/pagemap.h>

  #include <linux/mm.h>

  #include <linux/sched.h>
  #include <linux/module.h>

  #include <linux/writeback.h>
  #include <linux/device.h>

  #include <trace/events/writeback.h>

  static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);

  struct backing_dev_info default_backing_dev_info = {

  	.name		= "default",

  	.ra_pages	= VM_MAX_READAHEAD * 1024 / PAGE_CACHE_SIZE,
  	.state		= 0,
  	.capabilities	= BDI_CAP_MAP_COPY,

  };
  EXPORT_SYMBOL_GPL(default_backing_dev_info);

  struct backing_dev_info noop_backing_dev_info = {
  	.name		= "noop",

  	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,

  };
  EXPORT_SYMBOL_GPL(noop_backing_dev_info);

  static struct class *bdi_class;

  
  /*
   * bdi_lock protects updates to bdi_list and bdi_pending_list, as well as
   * reader side protection for bdi_pending_list. bdi_list has RCU reader side
   * locking.
   */

  DEFINE_SPINLOCK(bdi_lock);

  LIST_HEAD(bdi_list);

  LIST_HEAD(bdi_pending_list);
  
  static struct task_struct *sync_supers_tsk;
  static struct timer_list sync_supers_timer;
  
  static int bdi_sync_supers(void *);
  static void sync_supers_timer_fn(unsigned long);

  void bdi_lock_two(struct bdi_writeback *wb1, struct bdi_writeback *wb2)
  {
  	if (wb1 < wb2) {
  		spin_lock(&wb1->list_lock);
  		spin_lock_nested(&wb2->list_lock, 1);
  	} else {
  		spin_lock(&wb2->list_lock);
  		spin_lock_nested(&wb1->list_lock, 1);
  	}
  }

  #ifdef CONFIG_DEBUG_FS
  #include <linux/debugfs.h>
  #include <linux/seq_file.h>
  
  static struct dentry *bdi_debug_root;
  
  static void bdi_debug_init(void)
  {
  	bdi_debug_root = debugfs_create_dir("bdi", NULL);
  }
  
  static int bdi_debug_stats_show(struct seq_file *m, void *v)
  {
  	struct backing_dev_info *bdi = m->private;

  	struct bdi_writeback *wb = &bdi->wb;

  	unsigned long background_thresh;
  	unsigned long dirty_thresh;
  	unsigned long bdi_thresh;

  	unsigned long nr_dirty, nr_io, nr_more_io;

  	struct inode *inode;

  	nr_dirty = nr_io = nr_more_io = 0;

  	spin_lock(&wb->list_lock);

  	list_for_each_entry(inode, &wb->b_dirty, i_wb_list)

  		nr_dirty++;

  	list_for_each_entry(inode, &wb->b_io, i_wb_list)

  		nr_io++;

  	list_for_each_entry(inode, &wb->b_more_io, i_wb_list)

  		nr_more_io++;

  	spin_unlock(&wb->list_lock);

  	global_dirty_limits(&background_thresh, &dirty_thresh);
  	bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);

  
  #define K(x) ((x) << (PAGE_SHIFT - 10))
  	seq_printf(m,

  		   "BdiWriteback:       %10lu kB
  "
  		   "BdiReclaimable:     %10lu kB
  "
  		   "BdiDirtyThresh:     %10lu kB
  "
  		   "DirtyThresh:        %10lu kB
  "
  		   "BackgroundThresh:   %10lu kB
  "

  		   "BdiDirtied:         %10lu kB
  "

  		   "BdiWritten:         %10lu kB
  "
  		   "BdiWriteBandwidth:  %10lu kBps
  "
  		   "b_dirty:            %10lu
  "
  		   "b_io:               %10lu
  "
  		   "b_more_io:          %10lu
  "
  		   "bdi_list:           %10u
  "
  		   "state:              %10lx
  ",

  		   (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
  		   (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),

  		   K(bdi_thresh),
  		   K(dirty_thresh),
  		   K(background_thresh),

  		   (unsigned long) K(bdi_stat(bdi, BDI_DIRTIED)),

  		   (unsigned long) K(bdi_stat(bdi, BDI_WRITTEN)),

  		   (unsigned long) K(bdi->write_bandwidth),

  		   nr_dirty,
  		   nr_io,
  		   nr_more_io,

  		   !list_empty(&bdi->bdi_list), bdi->state);

  #undef K
  
  	return 0;
  }
  
  static int bdi_debug_stats_open(struct inode *inode, struct file *file)
  {
  	return single_open(file, bdi_debug_stats_show, inode->i_private);
  }
  
  static const struct file_operations bdi_debug_stats_fops = {
  	.open		= bdi_debug_stats_open,
  	.read		= seq_read,
  	.llseek		= seq_lseek,
  	.release	= single_release,
  };
  
  static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
  {
  	bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
  	bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
  					       bdi, &bdi_debug_stats_fops);
  }
  
  static void bdi_debug_unregister(struct backing_dev_info *bdi)
  {
  	debugfs_remove(bdi->debug_stats);
  	debugfs_remove(bdi->debug_dir);
  }
  #else
  static inline void bdi_debug_init(void)
  {
  }
  static inline void bdi_debug_register(struct backing_dev_info *bdi,
  				      const char *name)
  {
  }
  static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
  {
  }
  #endif

  static ssize_t read_ahead_kb_store(struct device *dev,
  				  struct device_attribute *attr,
  				  const char *buf, size_t count)
  {
  	struct backing_dev_info *bdi = dev_get_drvdata(dev);
  	char *end;
  	unsigned long read_ahead_kb;
  	ssize_t ret = -EINVAL;
  
  	read_ahead_kb = simple_strtoul(buf, &end, 10);
  	if (*buf && (end[0] == '\0' || (end[0] == '
  ' && end[1] == '\0'))) {
  		bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);
  		ret = count;
  	}
  	return ret;
  }
  
  #define K(pages) ((pages) << (PAGE_SHIFT - 10))
  
  #define BDI_SHOW(name, expr)						\
  static ssize_t name##_show(struct device *dev,				\
  			   struct device_attribute *attr, char *page)	\
  {									\
  	struct backing_dev_info *bdi = dev_get_drvdata(dev);		\
  									\
  	return snprintf(page, PAGE_SIZE-1, "%lld
  ", (long long)expr);	\
  }
  
  BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))

  static ssize_t min_ratio_store(struct device *dev,
  		struct device_attribute *attr, const char *buf, size_t count)
  {
  	struct backing_dev_info *bdi = dev_get_drvdata(dev);
  	char *end;
  	unsigned int ratio;
  	ssize_t ret = -EINVAL;
  
  	ratio = simple_strtoul(buf, &end, 10);
  	if (*buf && (end[0] == '\0' || (end[0] == '
  ' && end[1] == '\0'))) {
  		ret = bdi_set_min_ratio(bdi, ratio);
  		if (!ret)
  			ret = count;
  	}
  	return ret;
  }
  BDI_SHOW(min_ratio, bdi->min_ratio)

  static ssize_t max_ratio_store(struct device *dev,
  		struct device_attribute *attr, const char *buf, size_t count)
  {
  	struct backing_dev_info *bdi = dev_get_drvdata(dev);
  	char *end;
  	unsigned int ratio;
  	ssize_t ret = -EINVAL;
  
  	ratio = simple_strtoul(buf, &end, 10);
  	if (*buf && (end[0] == '\0' || (end[0] == '
  ' && end[1] == '\0'))) {
  		ret = bdi_set_max_ratio(bdi, ratio);
  		if (!ret)
  			ret = count;
  	}
  	return ret;
  }
  BDI_SHOW(max_ratio, bdi->max_ratio)

  #define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
  
  static struct device_attribute bdi_dev_attrs[] = {
  	__ATTR_RW(read_ahead_kb),

  	__ATTR_RW(min_ratio),

  	__ATTR_RW(max_ratio),

  	__ATTR_NULL,
  };
  
  static __init int bdi_class_init(void)
  {
  	bdi_class = class_create(THIS_MODULE, "bdi");

  	if (IS_ERR(bdi_class))
  		return PTR_ERR(bdi_class);

  	bdi_class->dev_attrs = bdi_dev_attrs;

  	bdi_debug_init();

  	return 0;
  }

  postcore_initcall(bdi_class_init);

  static int __init default_bdi_init(void)
  {
  	int err;

  	sync_supers_tsk = kthread_run(bdi_sync_supers, NULL, "sync_supers");
  	BUG_ON(IS_ERR(sync_supers_tsk));

  	setup_timer(&sync_supers_timer, sync_supers_timer_fn, 0);

  	bdi_arm_supers_timer();

  	err = bdi_init(&default_backing_dev_info);
  	if (!err)
  		bdi_register(&default_backing_dev_info, NULL, "default");

  	err = bdi_init(&noop_backing_dev_info);

  
  	return err;
  }
  subsys_initcall(default_bdi_init);

  int bdi_has_dirty_io(struct backing_dev_info *bdi)
  {
  	return wb_has_dirty_io(&bdi->wb);
  }

  /*

   * kupdated() used to do this. We cannot do it from the bdi_forker_thread()

   * or we risk deadlocking on ->s_umount. The longer term solution would be
   * to implement sync_supers_bdi() or similar and simply do it from the

   * bdi writeback thread individually.

   */
  static int bdi_sync_supers(void *unused)
  {
  	set_user_nice(current, 0);
  
  	while (!kthread_should_stop()) {
  		set_current_state(TASK_INTERRUPTIBLE);
  		schedule();
  
  		/*
  		 * Do this periodically, like kupdated() did before.
  		 */
  		sync_supers();
  	}
  
  	return 0;
  }

  void bdi_arm_supers_timer(void)

  {
  	unsigned long next;

  	if (!dirty_writeback_interval)
  		return;

  	next = msecs_to_jiffies(dirty_writeback_interval * 10) + jiffies;
  	mod_timer(&sync_supers_timer, round_jiffies_up(next));
  }
  
  static void sync_supers_timer_fn(unsigned long unused)
  {
  	wake_up_process(sync_supers_tsk);

  	bdi_arm_supers_timer();

  }

  static void wakeup_timer_fn(unsigned long data)
  {
  	struct backing_dev_info *bdi = (struct backing_dev_info *)data;
  
  	spin_lock_bh(&bdi->wb_lock);
  	if (bdi->wb.task) {

  		trace_writeback_wake_thread(bdi);

  		wake_up_process(bdi->wb.task);
  	} else {
  		/*
  		 * When bdi tasks are inactive for long time, they are killed.
  		 * In this case we have to wake-up the forker thread which
  		 * should create and run the bdi thread.
  		 */

  		trace_writeback_wake_forker_thread(bdi);

  		wake_up_process(default_backing_dev_info.wb.task);
  	}
  	spin_unlock_bh(&bdi->wb_lock);
  }
  
  /*
   * This function is used when the first inode for this bdi is marked dirty. It
   * wakes-up the corresponding bdi thread which should then take care of the
   * periodic background write-out of dirty inodes. Since the write-out would
   * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
   * set up a timer which wakes the bdi thread up later.
   *
   * Note, we wouldn't bother setting up the timer, but this function is on the
   * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
   * by delaying the wake-up.
   */
  void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
  {
  	unsigned long timeout;
  
  	timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
  	mod_timer(&bdi->wb.wakeup_timer, jiffies + timeout);
  }

  /*
   * Calculate the longest interval (jiffies) bdi threads are allowed to be
   * inactive.
   */
  static unsigned long bdi_longest_inactive(void)
  {
  	unsigned long interval;
  
  	interval = msecs_to_jiffies(dirty_writeback_interval * 10);
  	return max(5UL * 60 * HZ, interval);
  }

  /*
   * Clear pending bit and wakeup anybody waiting for flusher thread creation or
   * shutdown
   */
  static void bdi_clear_pending(struct backing_dev_info *bdi)
  {
  	clear_bit(BDI_pending, &bdi->state);
  	smp_mb__after_clear_bit();
  	wake_up_bit(&bdi->state, BDI_pending);
  }

  static int bdi_forker_thread(void *ptr)

  {
  	struct bdi_writeback *me = ptr;

  	current->flags |= PF_SWAPWRITE;

  	set_freezable();
  
  	/*
  	 * Our parent may run at a different priority, just set us to normal
  	 */
  	set_user_nice(current, 0);

  
  	for (;;) {

  		struct task_struct *task = NULL;

  		struct backing_dev_info *bdi;

  		enum {
  			NO_ACTION,   /* Nothing to do */
  			FORK_THREAD, /* Fork bdi thread */

  			KILL_THREAD, /* Kill inactive bdi thread */

  		} action = NO_ACTION;

  
  		/*
  		 * Temporary measure, we want to make sure we don't see
  		 * dirty data on the default backing_dev_info
  		 */

  		if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list)) {
  			del_timer(&me->wakeup_timer);

  			wb_do_writeback(me, 0);

  		}

  		spin_lock_bh(&bdi_lock);

  		/*
  		 * In the following loop we are going to check whether we have
  		 * some work to do without any synchronization with tasks

  		 * waking us up to do work for them. Set the task state here
  		 * so that we don't miss wakeups after verifying conditions.

  		 */

  		set_current_state(TASK_INTERRUPTIBLE);

  		list_for_each_entry(bdi, &bdi_list, bdi_list) {

  			bool have_dirty_io;
  
  			if (!bdi_cap_writeback_dirty(bdi) ||
  			     bdi_cap_flush_forker(bdi))

  				continue;

  			WARN(!test_bit(BDI_registered, &bdi->state),
  			     "bdi %p/%s is not registered!
  ", bdi, bdi->name);

  			have_dirty_io = !list_empty(&bdi->work_list) ||
  					wb_has_dirty_io(&bdi->wb);

  
  			/*

  			 * If the bdi has work to do, but the thread does not
  			 * exist - create it.

  			 */

  			if (!bdi->wb.task && have_dirty_io) {
  				/*
  				 * Set the pending bit - if someone will try to
  				 * unregister this bdi - it'll wait on this bit.
  				 */
  				set_bit(BDI_pending, &bdi->state);
  				action = FORK_THREAD;
  				break;
  			}

  			spin_lock(&bdi->wb_lock);

  			/*
  			 * If there is no work to do and the bdi thread was
  			 * inactive long enough - kill it. The wb_lock is taken
  			 * to make sure no-one adds more work to this bdi and
  			 * wakes the bdi thread up.
  			 */
  			if (bdi->wb.task && !have_dirty_io &&
  			    time_after(jiffies, bdi->wb.last_active +
  						bdi_longest_inactive())) {
  				task = bdi->wb.task;
  				bdi->wb.task = NULL;
  				spin_unlock(&bdi->wb_lock);
  				set_bit(BDI_pending, &bdi->state);
  				action = KILL_THREAD;
  				break;
  			}

  			spin_unlock(&bdi->wb_lock);

  		}

  		spin_unlock_bh(&bdi_lock);

  		/* Keep working if default bdi still has things to do */
  		if (!list_empty(&me->bdi->work_list))
  			__set_current_state(TASK_RUNNING);

  		switch (action) {
  		case FORK_THREAD:
  			__set_current_state(TASK_RUNNING);

  			task = kthread_create(bdi_writeback_thread, &bdi->wb,
  					      "flush-%s", dev_name(bdi->dev));

  			if (IS_ERR(task)) {
  				/*
  				 * If thread creation fails, force writeout of

  				 * the bdi from the thread. Hopefully 1024 is
  				 * large enough for efficient IO.

  				 */

  				writeback_inodes_wb(&bdi->wb, 1024,
  						    WB_REASON_FORKER_THREAD);

  			} else {
  				/*
  				 * The spinlock makes sure we do not lose
  				 * wake-ups when racing with 'bdi_queue_work()'.

  				 * And as soon as the bdi thread is visible, we
  				 * can start it.

  				 */

  				spin_lock_bh(&bdi->wb_lock);

  				bdi->wb.task = task;

  				spin_unlock_bh(&bdi->wb_lock);

  				wake_up_process(task);

  			}

  			bdi_clear_pending(bdi);

  			break;
  
  		case KILL_THREAD:
  			__set_current_state(TASK_RUNNING);
  			kthread_stop(task);

  			bdi_clear_pending(bdi);

  			break;

  		case NO_ACTION:

  			if (!wb_has_dirty_io(me) || !dirty_writeback_interval)
  				/*
  				 * There are no dirty data. The only thing we
  				 * should now care about is checking for
  				 * inactive bdi threads and killing them. Thus,
  				 * let's sleep for longer time, save energy and
  				 * be friendly for battery-driven devices.
  				 */
  				schedule_timeout(bdi_longest_inactive());

  			else

  				schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10));

  			try_to_freeze();

  			break;

  		}

  	}
  
  	return 0;
  }

  /*
   * Remove bdi from bdi_list, and ensure that it is no longer visible
   */
  static void bdi_remove_from_list(struct backing_dev_info *bdi)
  {
  	spin_lock_bh(&bdi_lock);
  	list_del_rcu(&bdi->bdi_list);
  	spin_unlock_bh(&bdi_lock);

  	synchronize_rcu_expedited();

  }

  int bdi_register(struct backing_dev_info *bdi, struct device *parent,
  		const char *fmt, ...)
  {

  	va_list args;

  	struct device *dev;

  	if (bdi->dev)	/* The driver needs to use separate queues per device */

  		return 0;

  	va_start(args, fmt);

  	dev = device_create_vargs(bdi_class, parent, MKDEV(0, 0), bdi, fmt, args);

  	va_end(args);

  	if (IS_ERR(dev))
  		return PTR_ERR(dev);

  	bdi->dev = dev;

  	/*
  	 * Just start the forker thread for our default backing_dev_info,
  	 * and add other bdi's to the list. They will get a thread created
  	 * on-demand when they need it.
  	 */
  	if (bdi_cap_flush_forker(bdi)) {
  		struct bdi_writeback *wb = &bdi->wb;

  		wb->task = kthread_run(bdi_forker_thread, wb, "bdi-%s",

  						dev_name(dev));

  		if (IS_ERR(wb->task))
  			return PTR_ERR(wb->task);

  	}
  
  	bdi_debug_register(bdi, dev_name(dev));

  	set_bit(BDI_registered, &bdi->state);

  
  	spin_lock_bh(&bdi_lock);
  	list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
  	spin_unlock_bh(&bdi_lock);

  	trace_writeback_bdi_register(bdi);

  	return 0;

  }
  EXPORT_SYMBOL(bdi_register);
  
  int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
  {
  	return bdi_register(bdi, NULL, "%u:%u", MAJOR(dev), MINOR(dev));
  }
  EXPORT_SYMBOL(bdi_register_dev);

  /*
   * Remove bdi from the global list and shutdown any threads we have running
   */
  static void bdi_wb_shutdown(struct backing_dev_info *bdi)

  {

  	if (!bdi_cap_writeback_dirty(bdi))
  		return;
  
  	/*

  	 * Make sure nobody finds us on the bdi_list anymore

  	 */

  	bdi_remove_from_list(bdi);

  
  	/*

  	 * If setup is pending, wait for that to complete first

  	 */

  	wait_on_bit(&bdi->state, BDI_pending, bdi_sched_wait,
  			TASK_UNINTERRUPTIBLE);

  
  	/*

  	 * Finally, kill the kernel thread. We don't need to be RCU

  	 * safe anymore, since the bdi is gone from visibility.

  	 */

  	if (bdi->wb.task)

  		kthread_stop(bdi->wb.task);

  }

  /*
   * This bdi is going away now, make sure that no super_blocks point to it
   */
  static void bdi_prune_sb(struct backing_dev_info *bdi)
  {
  	struct super_block *sb;
  
  	spin_lock(&sb_lock);
  	list_for_each_entry(sb, &super_blocks, s_list) {
  		if (sb->s_bdi == bdi)

  			sb->s_bdi = &default_backing_dev_info;

  	}
  	spin_unlock(&sb_lock);
  }

  void bdi_unregister(struct backing_dev_info *bdi)
  {
  	if (bdi->dev) {

  		bdi_set_min_ratio(bdi, 0);

  		trace_writeback_bdi_unregister(bdi);

  		bdi_prune_sb(bdi);

  		del_timer_sync(&bdi->wb.wakeup_timer);

  		if (!bdi_cap_flush_forker(bdi))
  			bdi_wb_shutdown(bdi);

  		bdi_debug_unregister(bdi);

  		device_unregister(bdi->dev);
  		bdi->dev = NULL;
  	}
  }
  EXPORT_SYMBOL(bdi_unregister);

  static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
  {
  	memset(wb, 0, sizeof(*wb));
  
  	wb->bdi = bdi;
  	wb->last_old_flush = jiffies;
  	INIT_LIST_HEAD(&wb->b_dirty);
  	INIT_LIST_HEAD(&wb->b_io);
  	INIT_LIST_HEAD(&wb->b_more_io);

  	spin_lock_init(&wb->list_lock);

  	setup_timer(&wb->wakeup_timer, wakeup_timer_fn, (unsigned long)bdi);
  }

  /*
   * Initial write bandwidth: 100 MB/s
   */
  #define INIT_BW		(100 << (20 - PAGE_SHIFT))

  int bdi_init(struct backing_dev_info *bdi)
  {

  	int i, err;

  	bdi->dev = NULL;

  	bdi->min_ratio = 0;

  	bdi->max_ratio = 100;
  	bdi->max_prop_frac = PROP_FRAC_BASE;

  	spin_lock_init(&bdi->wb_lock);

  	INIT_LIST_HEAD(&bdi->bdi_list);

  	INIT_LIST_HEAD(&bdi->work_list);
  
  	bdi_wb_init(&bdi->wb, bdi);

  	for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {

  		err = percpu_counter_init(&bdi->bdi_stat[i], 0);

  		if (err)
  			goto err;
  	}
  
  	bdi->dirty_exceeded = 0;

  
  	bdi->bw_time_stamp = jiffies;
  	bdi->written_stamp = 0;

  	bdi->balanced_dirty_ratelimit = INIT_BW;

  	bdi->dirty_ratelimit = INIT_BW;

  	bdi->write_bandwidth = INIT_BW;
  	bdi->avg_write_bandwidth = INIT_BW;

  	err = prop_local_init_percpu(&bdi->completions);
  
  	if (err) {
  err:

  		while (i--)

  			percpu_counter_destroy(&bdi->bdi_stat[i]);

  	}
  
  	return err;
  }
  EXPORT_SYMBOL(bdi_init);
  
  void bdi_destroy(struct backing_dev_info *bdi)
  {
  	int i;

  	/*
  	 * Splice our entries to the default_backing_dev_info, if this
  	 * bdi disappears
  	 */
  	if (bdi_has_dirty_io(bdi)) {
  		struct bdi_writeback *dst = &default_backing_dev_info.wb;

  		bdi_lock_two(&bdi->wb, dst);

  		list_splice(&bdi->wb.b_dirty, &dst->b_dirty);
  		list_splice(&bdi->wb.b_io, &dst->b_io);
  		list_splice(&bdi->wb.b_more_io, &dst->b_more_io);

  		spin_unlock(&bdi->wb.list_lock);
  		spin_unlock(&dst->list_lock);

  	}

  	bdi_unregister(bdi);

  	/*
  	 * If bdi_unregister() had already been called earlier, the
  	 * wakeup_timer could still be armed because bdi_prune_sb()
  	 * can race with the bdi_wakeup_thread_delayed() calls from
  	 * __mark_inode_dirty().
  	 */
  	del_timer_sync(&bdi->wb.wakeup_timer);

  	for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
  		percpu_counter_destroy(&bdi->bdi_stat[i]);

  
  	prop_local_destroy_percpu(&bdi->completions);

  }
  EXPORT_SYMBOL(bdi_destroy);

  /*
   * For use from filesystems to quickly init and register a bdi associated
   * with dirty writeback
   */
  int bdi_setup_and_register(struct backing_dev_info *bdi, char *name,
  			   unsigned int cap)
  {
  	char tmp[32];
  	int err;
  
  	bdi->name = name;
  	bdi->capabilities = cap;
  	err = bdi_init(bdi);
  	if (err)
  		return err;
  
  	sprintf(tmp, "%.28s%s", name, "-%d");
  	err = bdi_register(bdi, NULL, tmp, atomic_long_inc_return(&bdi_seq));
  	if (err) {
  		bdi_destroy(bdi);
  		return err;
  	}
  
  	return 0;
  }
  EXPORT_SYMBOL(bdi_setup_and_register);

  static wait_queue_head_t congestion_wqh[2] = {
  		__WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
  		__WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
  	};

  static atomic_t nr_bdi_congested[2];

  void clear_bdi_congested(struct backing_dev_info *bdi, int sync)

  {
  	enum bdi_state bit;

  	wait_queue_head_t *wqh = &congestion_wqh[sync];

  	bit = sync ? BDI_sync_congested : BDI_async_congested;

  	if (test_and_clear_bit(bit, &bdi->state))
  		atomic_dec(&nr_bdi_congested[sync]);

  	smp_mb__after_clear_bit();
  	if (waitqueue_active(wqh))
  		wake_up(wqh);
  }
  EXPORT_SYMBOL(clear_bdi_congested);

  void set_bdi_congested(struct backing_dev_info *bdi, int sync)

  {
  	enum bdi_state bit;

  	bit = sync ? BDI_sync_congested : BDI_async_congested;

  	if (!test_and_set_bit(bit, &bdi->state))
  		atomic_inc(&nr_bdi_congested[sync]);

  }
  EXPORT_SYMBOL(set_bdi_congested);
  
  /**
   * congestion_wait - wait for a backing_dev to become uncongested

   * @sync: SYNC or ASYNC IO

   * @timeout: timeout in jiffies
   *
   * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
   * write congestion.  If no backing_devs are congested then just wait for the
   * next write to be completed.
   */

  long congestion_wait(int sync, long timeout)

  {
  	long ret;

  	unsigned long start = jiffies;

  	DEFINE_WAIT(wait);

  	wait_queue_head_t *wqh = &congestion_wqh[sync];

  
  	prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
  	ret = io_schedule_timeout(timeout);
  	finish_wait(wqh, &wait);

  
  	trace_writeback_congestion_wait(jiffies_to_usecs(timeout),
  					jiffies_to_usecs(jiffies - start));

  	return ret;
  }
  EXPORT_SYMBOL(congestion_wait);

  /**
   * wait_iff_congested - Conditionally wait for a backing_dev to become uncongested or a zone to complete writes
   * @zone: A zone to check if it is heavily congested
   * @sync: SYNC or ASYNC IO
   * @timeout: timeout in jiffies
   *
   * In the event of a congested backing_dev (any backing_dev) and the given
   * @zone has experienced recent congestion, this waits for up to @timeout
   * jiffies for either a BDI to exit congestion of the given @sync queue
   * or a write to complete.
   *

   * In the absence of zone congestion, cond_resched() is called to yield

   * the processor if necessary but otherwise does not sleep.
   *
   * The return value is 0 if the sleep is for the full timeout. Otherwise,
   * it is the number of jiffies that were still remaining when the function
   * returned. return_value == timeout implies the function did not sleep.
   */
  long wait_iff_congested(struct zone *zone, int sync, long timeout)
  {
  	long ret;
  	unsigned long start = jiffies;
  	DEFINE_WAIT(wait);
  	wait_queue_head_t *wqh = &congestion_wqh[sync];
  
  	/*
  	 * If there is no congestion, or heavy congestion is not being
  	 * encountered in the current zone, yield if necessary instead
  	 * of sleeping on the congestion queue
  	 */
  	if (atomic_read(&nr_bdi_congested[sync]) == 0 ||
  			!zone_is_reclaim_congested(zone)) {
  		cond_resched();
  
  		/* In case we scheduled, work out time remaining */
  		ret = timeout - (jiffies - start);
  		if (ret < 0)
  			ret = 0;
  
  		goto out;
  	}
  
  	/* Sleep until uncongested or a write happens */
  	prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
  	ret = io_schedule_timeout(timeout);
  	finish_wait(wqh, &wait);
  
  out:
  	trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout),
  					jiffies_to_usecs(jiffies - start));
  
  	return ret;
  }
  EXPORT_SYMBOL(wait_iff_congested);