Esempio n. 1
0
/*
 * 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)
{
	long nr_reclaimable, bdi_nr_reclaimable;
	long nr_writeback, bdi_nr_writeback;
	long background_thresh;
	long dirty_thresh;
	long bdi_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,
			.range_cyclic	= 1,
		};

		get_dirty_limits(&background_thresh, &dirty_thresh,
				&bdi_thresh, bdi);

		nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
					global_page_state(NR_UNSTABLE_NFS);
		nr_writeback = global_page_state(NR_WRITEBACK);

		bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
		bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);

		if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
			break;

		/*
		 * Throttle it only when the background writeback cannot
		 * catch-up. This avoids (excessively) small writeouts
		 * when the bdi limits are ramping up.
		 */
		if (nr_reclaimable + nr_writeback <
				(background_thresh + dirty_thresh) / 2)
			break;

		if (!bdi->dirty_exceeded)
			bdi->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 (bdi_nr_reclaimable) {
			writeback_inodes(&wbc);
			pages_written += write_chunk - wbc.nr_to_write;
			get_dirty_limits(&background_thresh, &dirty_thresh,
				       &bdi_thresh, bdi);
		}

		/*
		 * In order to avoid the stacked BDI deadlock we need
		 * to ensure we accurately count the 'dirty' pages when
		 * the threshold is low.
		 *
		 * Otherwise it would be possible to get thresh+n pages
		 * reported dirty, even though there are thresh-m pages
		 * actually dirty; with m+n sitting in the percpu
		 * deltas.
		 */
		if (bdi_thresh < 2*bdi_stat_error(bdi)) {
			bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
			bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK);
		} else if (bdi_nr_reclaimable) {
			bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
			bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
		}

		if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
			break;
		if (pages_written >= write_chunk)
			break;		/* We've done our duty */

		congestion_wait(WRITE, HZ/10);
	}

	if (bdi_nr_reclaimable + bdi_nr_writeback < bdi_thresh &&
			bdi->dirty_exceeded)
		bdi->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 && (global_page_state(NR_FILE_DIRTY)
					  + global_page_state(NR_UNSTABLE_NFS)
					  > background_thresh)))
		pdflush_operation(background_writeout, 0);
}

void set_page_dirty_balance(struct page *page, int page_mkwrite)
{
	if (set_page_dirty(page) || page_mkwrite) {
		struct address_space *mapping = page_mapping(page);

		if (mapping)
			balance_dirty_pages_ratelimited(mapping);
	}
}

/**
 * balance_dirty_pages_ratelimited_nr - balance dirty memory state
 * @mapping: address_space which was dirtied
 * @nr_pages_dirtied: number of pages which the caller has just 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_nr(struct address_space *mapping,
					unsigned long nr_pages_dirtied)
{
	static DEFINE_PER_CPU(unsigned long, ratelimits) = 0;
	unsigned long ratelimit;
	unsigned long *p;

	ratelimit = ratelimit_pages;
	if (mapping->backing_dev_info->dirty_exceeded)
		ratelimit = 8;

	/*
	 * Check the rate limiting. Also, we do not want to throttle real-time
	 * tasks in balance_dirty_pages(). Period.
	 */
	preempt_disable();
	p =  &__get_cpu_var(ratelimits);
	*p += nr_pages_dirtied;
	if (unlikely(*p >= ratelimit)) {
		*p = 0;
		preempt_enable();
		balance_dirty_pages(mapping);
		return;
	}
	preempt_enable();
}
EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr);

void throttle_vm_writeout(gfp_t gfp_mask)
{
	long background_thresh;
	long dirty_thresh;

        for ( ; ; ) {
		get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);

                /*
                 * Boost the allowable dirty threshold a bit for page
                 * allocators so they don't get DoS'ed by heavy writers
                 */
                dirty_thresh += dirty_thresh / 10;      /* wheeee... */

                if (global_page_state(NR_UNSTABLE_NFS) +
			global_page_state(NR_WRITEBACK) <= dirty_thresh)
                        	break;
                congestion_wait(WRITE, HZ/10);

		/*
		 * The caller might hold locks which can prevent IO completion
		 * or progress in the filesystem.  So we cannot just sit here
		 * waiting for IO to complete.
		 */
		if ((gfp_mask & (__GFP_FS|__GFP_IO)) != (__GFP_FS|__GFP_IO))
			break;
        }
}
Esempio n. 2
0
/*
 * 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 the writeback threads are woken to
 * perform some writeout.
 */
static void balance_dirty_pages(struct address_space *mapping,
				unsigned long write_chunk)
{
	long nr_reclaimable, bdi_nr_reclaimable;
	long nr_writeback, bdi_nr_writeback;
	long ub_dirty, ub_writeback;
	long ub_thresh, ub_background_thresh;
	unsigned long background_thresh;
	unsigned long dirty_thresh;
	unsigned long bdi_thresh;
	unsigned long pages_written = 0;
	unsigned long pause = 1;
	struct user_beancounter *ub = get_io_ub();

	struct backing_dev_info *bdi = mapping->backing_dev_info;

	for (;;) {
		struct writeback_control wbc = {
			.sync_mode	= WB_SYNC_NONE,
			.older_than_this = NULL,
			.nr_to_write	= write_chunk,
			.range_cyclic	= 1,
		};

		get_dirty_limits(&background_thresh, &dirty_thresh,
				&bdi_thresh, bdi);

		if (ub_dirty_limits(&ub_background_thresh, &ub_thresh, ub)) {
			ub_dirty = ub_stat_get(ub, dirty_pages);
			ub_writeback = ub_stat_get(ub, writeback_pages);
		} else {
			ub_dirty = ub_writeback = 0;
			ub_thresh = ub_background_thresh = LONG_MAX / 2;
		}

		nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
					global_page_state(NR_UNSTABLE_NFS);
		nr_writeback = global_page_state(NR_WRITEBACK);

		bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
		bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);

		/*
		 * Check thresholds, set dirty_exceeded flags and
		 * start background writeback before throttling.
		 */
		if (bdi_nr_reclaimable + bdi_nr_writeback > bdi_thresh) {
			if (!bdi->dirty_exceeded)
				bdi->dirty_exceeded = 1;
			if (!writeback_in_progress(bdi))
				bdi_start_background_writeback(bdi, NULL);
		} else if (ub_dirty + ub_writeback > ub_thresh) {
			if (!test_bit(UB_DIRTY_EXCEEDED, &ub->ub_flags))
				set_bit(UB_DIRTY_EXCEEDED, &ub->ub_flags);
			if (!writeback_in_progress(bdi))
				bdi_start_background_writeback(bdi, ub);
		} else
			break;

		/*
		 * Throttle it only when the background writeback cannot
		 * catch-up. This avoids (excessively) small writeouts
		 * when the bdi limits are ramping up.
		 */
		if (bdi_cap_account_writeback(bdi) &&
		    nr_reclaimable + nr_writeback <
				(background_thresh + dirty_thresh) / 2 &&
		    ub_dirty + ub_writeback <
				(ub_background_thresh + ub_thresh) / 2)
			break;

		/* 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.
		 * Only move pages to writeback if this bdi is over its
		 * threshold otherwise wait until the disk writes catch
		 * up.
		 */
		trace_wbc_balance_dirty_start(&wbc, bdi);
		if (bdi_nr_reclaimable > bdi_thresh) {
			writeback_inodes_wb(&bdi->wb, &wbc);
			pages_written += write_chunk - wbc.nr_to_write;
			trace_wbc_balance_dirty_written(&wbc, bdi);
			get_dirty_limits(&background_thresh, &dirty_thresh,
				       &bdi_thresh, bdi);
		} else if (ub_dirty > ub_thresh) {
			wbc.wb_ub = ub;
			writeback_inodes_wb(&bdi->wb, &wbc);
			pages_written += write_chunk - wbc.nr_to_write;
			trace_wbc_balance_dirty_written(&wbc, bdi);
			ub_dirty = ub_stat_get(ub, dirty_pages);
			ub_writeback = ub_stat_get(ub, writeback_pages);
			wbc.wb_ub = NULL;
		}

		/*
		 * In order to avoid the stacked BDI deadlock we need
		 * to ensure we accurately count the 'dirty' pages when
		 * the threshold is low.
		 *
		 * Otherwise it would be possible to get thresh+n pages
		 * reported dirty, even though there are thresh-m pages
		 * actually dirty; with m+n sitting in the percpu
		 * deltas.
		 */
		if (bdi_thresh < 2*bdi_stat_error(bdi)) {
			bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
			bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK);
		} else if (bdi_nr_reclaimable) {
			bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
			bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
		}

		/* fixup ub-stat per-cpu drift to avoid false-positive */
		if (ub_dirty + ub_writeback > ub_thresh &&
		    ub_dirty + ub_writeback - ub_thresh <
				    UB_STAT_BATCH * num_possible_cpus()) {
			ub_dirty = ub_stat_get_exact(ub, dirty_pages);
			ub_writeback = ub_stat_get_exact(ub, writeback_pages);
		}

		if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh &&
		    ub_dirty + ub_writeback <= ub_thresh)
			break;

		if (pages_written >= write_chunk)
			break;		/* We've done our duty */

		trace_wbc_balance_dirty_wait(&wbc, bdi);
		__set_current_state(TASK_KILLABLE);
		io_schedule_timeout(pause);

		/*
		 * Increase the delay for each loop, up to our previous
		 * default of taking a 100ms nap.
		 */
		pause <<= 1;
		if (pause > HZ / 10)
			pause = HZ / 10;

		if (fatal_signal_pending(current))
			break;
	}

	if(pages_written) trace_mm_balancedirty_writeout(pages_written);
	if (bdi_nr_reclaimable + bdi_nr_writeback < bdi_thresh &&
			bdi->dirty_exceeded)
		bdi->dirty_exceeded = 0;

	if (ub_dirty + ub_writeback < ub_thresh &&
	    test_bit(UB_DIRTY_EXCEEDED, &ub->ub_flags))
		clear_bit(UB_DIRTY_EXCEEDED, &ub->ub_flags);

	virtinfo_notifier_call(VITYPE_IO, VIRTINFO_IO_BALANCE_DIRTY,
			       (void*)write_chunk);

	/*
	 * Even if this is filtered writeback for other ub it will write
	 * inodes for this ub, because ub->dirty_exceeded is set.
	 */
	if (writeback_in_progress(bdi))
		return;

	/*
	 * 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 && ((global_page_state(NR_FILE_DIRTY)
			       + global_page_state(NR_UNSTABLE_NFS))
					  > background_thresh)))
		bdi_start_background_writeback(bdi, NULL);
	else if ((laptop_mode && pages_written) ||
		 (!laptop_mode && ub_dirty > ub_background_thresh))
		bdi_start_background_writeback(bdi, ub);
}

void set_page_dirty_balance(struct page *page, int page_mkwrite)
{
	if (set_page_dirty(page) || page_mkwrite) {
		struct address_space *mapping = page_mapping(page);

		if (mapping)
			balance_dirty_pages_ratelimited(mapping);
	}
}

static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;

/**
 * balance_dirty_pages_ratelimited_nr - balance dirty memory state
 * @mapping: address_space which was dirtied
 * @nr_pages_dirtied: number of pages which the caller has just 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_nr(struct address_space *mapping,
					unsigned long nr_pages_dirtied)
{
	unsigned long ratelimit;
	unsigned long *p;

	ratelimit = ratelimit_pages;
	if (mapping->backing_dev_info->dirty_exceeded ||
	    test_bit(UB_DIRTY_EXCEEDED, &get_io_ub()->ub_flags))
		ratelimit = 8;

	/*
	 * Check the rate limiting. Also, we do not want to throttle real-time
	 * tasks in balance_dirty_pages(). Period.
	 */
	preempt_disable();
	p =  &__get_cpu_var(bdp_ratelimits);
	*p += nr_pages_dirtied;
	if (unlikely(*p >= ratelimit)) {
		ratelimit = sync_writeback_pages(*p);
		*p = 0;
		preempt_enable();
		balance_dirty_pages(mapping, ratelimit);
		return;
	}
	preempt_enable();
}
Esempio n. 3
0
/*
 * 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 the writeback threads are woken to
 * perform some writeout.
 */
static void balance_dirty_pages(struct address_space *mapping,
				unsigned long write_chunk)
{
	long nr_reclaimable, bdi_nr_reclaimable;
	long nr_writeback, bdi_nr_writeback;
	unsigned long background_thresh;
	unsigned long dirty_thresh;
	unsigned long bdi_thresh;
	unsigned long pages_written = 0;
	unsigned long pause = 1;
	bool dirty_exceeded = false;
	struct backing_dev_info *bdi = mapping->backing_dev_info;

	for (;;) {
		struct writeback_control wbc = {
			.sync_mode	= WB_SYNC_NONE,
			.older_than_this = NULL,
			.nr_to_write	= write_chunk,
			.range_cyclic	= 1,
		};

		nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
					global_page_state(NR_UNSTABLE_NFS);
		nr_writeback = global_page_state(NR_WRITEBACK);

		global_dirty_limits(&background_thresh, &dirty_thresh);

		/*
		 * Throttle it only when the background writeback cannot
		 * catch-up. This avoids (excessively) small writeouts
		 * when the bdi limits are ramping up.
		 */
		if (nr_reclaimable + nr_writeback <=
				(background_thresh + dirty_thresh) / 2)
			break;

		bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
		bdi_thresh = task_dirty_limit(current, bdi_thresh);

		/*
		 * In order to avoid the stacked BDI deadlock we need
		 * to ensure we accurately count the 'dirty' pages when
		 * the threshold is low.
		 *
		 * Otherwise it would be possible to get thresh+n pages
		 * reported dirty, even though there are thresh-m pages
		 * actually dirty; with m+n sitting in the percpu
		 * deltas.
		 */
		if (bdi_thresh < 2*bdi_stat_error(bdi)) {
			bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
			bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK);
		} else {
			bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
			bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
		}

		/*
		 * The bdi thresh is somehow "soft" limit derived from the
		 * global "hard" limit. The former helps to prevent heavy IO
		 * bdi or process from holding back light ones; The latter is
		 * the last resort safeguard.
		 */
		dirty_exceeded =
			(bdi_nr_reclaimable + bdi_nr_writeback > bdi_thresh)
			|| (nr_reclaimable + nr_writeback > dirty_thresh);

		if (!dirty_exceeded)
			break;

		if (!bdi->dirty_exceeded)
			bdi->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.
		 * Only move pages to writeback if this bdi is over its
		 * threshold otherwise wait until the disk writes catch
		 * up.
		 */
		trace_wbc_balance_dirty_start(&wbc, bdi);
		if (bdi_nr_reclaimable > bdi_thresh) {
			writeback_inodes_wb(&bdi->wb, &wbc);
			pages_written += write_chunk - wbc.nr_to_write;
			trace_wbc_balance_dirty_written(&wbc, bdi);
			if (pages_written >= write_chunk)
				break;		/* We've done our duty */
		}
		trace_wbc_balance_dirty_wait(&wbc, bdi);
		__set_current_state(TASK_UNINTERRUPTIBLE);
		io_schedule_timeout(pause);

		/*
		 * Increase the delay for each loop, up to our previous
		 * default of taking a 100ms nap.
		 */
		pause <<= 1;
		if (pause > HZ / 10)
			break;
	}

	if (!dirty_exceeded && bdi->dirty_exceeded)
		bdi->dirty_exceeded = 0;

	if (writeback_in_progress(bdi))
		return;

	/*
	 * 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)))
		bdi_start_background_writeback(bdi);
}

void set_page_dirty_balance(struct page *page, int page_mkwrite)
{
	if (set_page_dirty(page) || page_mkwrite) {
		struct address_space *mapping = page_mapping(page);

		if (mapping)
			balance_dirty_pages_ratelimited(mapping);
	}
}

static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;

/**
 * balance_dirty_pages_ratelimited_nr - balance dirty memory state
 * @mapping: address_space which was dirtied
 * @nr_pages_dirtied: number of pages which the caller has just 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_nr(struct address_space *mapping,
					unsigned long nr_pages_dirtied)
{
	unsigned long ratelimit;
	unsigned long *p;

	ratelimit = ratelimit_pages;
	if (mapping->backing_dev_info->dirty_exceeded)
		ratelimit = 8;

	/*
	 * Check the rate limiting. Also, we do not want to throttle real-time
	 * tasks in balance_dirty_pages(). Period.
	 */
	preempt_disable();
	p =  &__get_cpu_var(bdp_ratelimits);
	*p += nr_pages_dirtied;
	if (unlikely(*p >= ratelimit)) {
		ratelimit = sync_writeback_pages(*p);
		*p = 0;
		preempt_enable();
		balance_dirty_pages(mapping, ratelimit);
		return;
	}
	preempt_enable();
}
static void balance_dirty_pages(struct address_space *mapping,
				unsigned long write_chunk)
{
	long nr_reclaimable, bdi_nr_reclaimable;
	long nr_writeback, bdi_nr_writeback;
	unsigned long background_thresh;
	unsigned long dirty_thresh;
	unsigned long bdi_thresh;
	unsigned long pages_written = 0;
	unsigned long pause = 1;

	struct backing_dev_info *bdi = mapping->backing_dev_info;

	for (;;) {
		struct writeback_control wbc = {
			.sync_mode	= WB_SYNC_NONE,
			.older_than_this = NULL,
			.nr_to_write	= write_chunk,
			.range_cyclic	= 1,
		};

		get_dirty_limits(&background_thresh, &dirty_thresh,
				&bdi_thresh, bdi);

		nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
					global_page_state(NR_UNSTABLE_NFS);
		nr_writeback = global_page_state(NR_WRITEBACK);

		bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
		bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);

		if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
			break;

		/*
		 * Throttle it only when the background writeback cannot
		 * catch-up. This avoids (excessively) small writeouts
		 * when the bdi limits are ramping up.
		 */
		if (nr_reclaimable + nr_writeback <
				(background_thresh + dirty_thresh) / 2)
			break;

		if (!bdi->dirty_exceeded)
			bdi->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.
		 * Only move pages to writeback if this bdi is over its
		 * threshold otherwise wait until the disk writes catch
		 * up.
		 */
		if (bdi_nr_reclaimable > bdi_thresh) {
			writeback_inodes_wb(&bdi->wb, &wbc);
			pages_written += write_chunk - wbc.nr_to_write;
			get_dirty_limits(&background_thresh, &dirty_thresh,
				       &bdi_thresh, bdi);
		}

		/*
		 * In order to avoid the stacked BDI deadlock we need
		 * to ensure we accurately count the 'dirty' pages when
		 * the threshold is low.
		 *
		 * Otherwise it would be possible to get thresh+n pages
		 * reported dirty, even though there are thresh-m pages
		 * actually dirty; with m+n sitting in the percpu
		 * deltas.
		 */
		if (bdi_thresh < 2*bdi_stat_error(bdi)) {
			bdi_nr_reclaimable = bdi_stat_sum(bdi, BDI_RECLAIMABLE);
			bdi_nr_writeback = bdi_stat_sum(bdi, BDI_WRITEBACK);
		} else if (bdi_nr_reclaimable) {
			bdi_nr_reclaimable = bdi_stat(bdi, BDI_RECLAIMABLE);
			bdi_nr_writeback = bdi_stat(bdi, BDI_WRITEBACK);
		}

		if (bdi_nr_reclaimable + bdi_nr_writeback <= bdi_thresh)
			break;
		if (pages_written >= write_chunk)
			break;		/* We've done our duty */

		__set_current_state(TASK_INTERRUPTIBLE);
		io_schedule_timeout(pause);

		/*
		 * Increase the delay for each loop, up to our previous
		 * default of taking a 100ms nap.
		 */
		pause <<= 1;
		if (pause > HZ / 10)
			pause = HZ / 10;
	}

	if (bdi_nr_reclaimable + bdi_nr_writeback < bdi_thresh &&
			bdi->dirty_exceeded)
		bdi->dirty_exceeded = 0;

	if (writeback_in_progress(bdi))
		return;

	/*
	 * 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 && ((global_page_state(NR_FILE_DIRTY)
			       + global_page_state(NR_UNSTABLE_NFS))
					  > background_thresh)))
		bdi_start_background_writeback(bdi);
}

void set_page_dirty_balance(struct page *page, int page_mkwrite)
{
	if (set_page_dirty(page) || page_mkwrite) {
		struct address_space *mapping = page_mapping(page);

		if (mapping)
			balance_dirty_pages_ratelimited(mapping);
	}
}

static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;

void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
					unsigned long nr_pages_dirtied)
{
	unsigned long ratelimit;
	unsigned long *p;

	ratelimit = ratelimit_pages;
	if (mapping->backing_dev_info->dirty_exceeded)
		ratelimit = 8;

	/*
	 * Check the rate limiting. Also, we do not want to throttle real-time
	 * tasks in balance_dirty_pages(). Period.
	 */
	preempt_disable();
	p =  &__get_cpu_var(bdp_ratelimits);
	*p += nr_pages_dirtied;
	if (unlikely(*p >= ratelimit)) {
		ratelimit = sync_writeback_pages(*p);
		*p = 0;
		preempt_enable();
		balance_dirty_pages(mapping, ratelimit);
		return;
	}
	preempt_enable();
}