[PATCH 0/15] Per-bdi writeback flusher threads v10

[PATCH 0/15] Per-bdi writeback flusher threads v10

[Jens Axboe]

Hi,

Here's the 10th version of the writeback patches. Changes since v9:

- Fix bdi task exit race leaving work on the list, flush it after we
  know we cannot be found anymore.
- Rename flusher tasks from bdi-foo to flush-foo. Should make it more
  clear to the casual observer.
- Fix a problem with the btrfs bdi register patch that would spew
  warnings for > 1 mounted btrfs file system.
- Rebase to current -git, there were some conflicts with the latest work
  from viro/hch.
- Fix a block layer core problem were stacked devices would overwrite
  the bdi state, causing problems and warning spew.
- In bdi_writeback_all(), in the race occurence of a work allocation
  failure, restart scanning from the beginning. Then we can drop the
  bdi_lock mutex before diving into bdi specific writeback.
- Convert bdi_lock to a spinlock.
- Use spin_trylock() in bdi_writeback_all(), if this isn't a data
  integrity writeback. Debatable, I kind of like it...
- Get rid of BDI_CAP_FLUSH_FORKER, just check for match with the
  default_backing_dev_info.
- Fix race in list checking in bdi_forker_task().


For ease of patching, I've put the full diff here:

  http://kernel.dk/writeback-v10.patch

and also stored this in a writeback-v10 branch that will not change,
you can pull that into Linus tree from here:

  git://git.kernel.dk/linux-2.6-block.git writeback-v10

Please test and report results/interesting finds. Thanks!

 b/block/blk-core.c            |    6 
 b/block/blk-settings.c        |    4 
 b/drivers/block/aoe/aoeblk.c  |    1 
 b/drivers/char/mem.c          |    1 
 b/fs/btrfs/disk-io.c          |   27 -
 b/fs/buffer.c                 |    2 
 b/fs/char_dev.c               |    1 
 b/fs/configfs/inode.c         |    1 
 b/fs/fs-writeback.c           |  818 +++++++++++++++++++++++++++-------
 b/fs/fuse/inode.c             |    1 
 b/fs/hugetlbfs/inode.c        |    1 
 b/fs/nfs/client.c             |    1 
 b/fs/ocfs2/dlm/dlmfs.c        |    1 
 b/fs/ramfs/inode.c            |    1 
 b/fs/super.c                  |    3 
 b/fs/sysfs/inode.c            |    1 
 b/fs/ubifs/super.c            |    4 
 b/include/linux/backing-dev.h |   72 ++
 b/include/linux/fs.h          |   11 
 b/include/linux/writeback.h   |   15 
 b/kernel/cgroup.c             |    1 
 b/mm/Makefile                 |    2 
 b/mm/backing-dev.c            |  519 +++++++++++++++++++++
 b/mm/page-writeback.c         |  157 ------
 b/mm/swap_state.c             |    1 
 b/mm/vmscan.c                 |    2 
 mm/pdflush.c                  |  269 -----------
 27 files changed, 1317 insertions(+), 606 deletions(-)

-- 
Jens Axboe

[PATCH 01/15] block: don't overwrite bdi->state after bdi_init() has been run

[Jens Axboe]

Move the defaults to where we do the init of the backing_dev_info.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 block/blk-core.c     |    5 +++++
 block/blk-settings.c |    4 ----
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index f6452f6..94d88fa 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -498,6 +498,11 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
 
 	q->backing_dev_info.unplug_io_fn = blk_backing_dev_unplug;
 	q->backing_dev_info.unplug_io_data = q;
+	q->backing_dev_info.ra_pages =
+			(VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
+	q->backing_dev_info.state = 0;
+	q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
+
 	err = bdi_init(&q->backing_dev_info);
 	if (err) {
 		kmem_cache_free(blk_requestq_cachep, q);
diff --git a/block/blk-settings.c b/block/blk-settings.c
index d71cedc..138610b 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -129,10 +129,6 @@ void blk_queue_make_request(struct request_queue *q, make_request_fn *mfn)
 	blk_queue_max_segment_size(q, MAX_SEGMENT_SIZE);
 
 	q->make_request_fn = mfn;
-	q->backing_dev_info.ra_pages =
-			(VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
-	q->backing_dev_info.state = 0;
-	q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
 	blk_queue_max_sectors(q, SAFE_MAX_SECTORS);
 	blk_queue_logical_block_size(q, 512);
 	blk_queue_dma_alignment(q, 511);
-- 
1.6.3.rc0.1.gf800

[PATCH 02/15] btrfs: properly register fs backing device

[Jens Axboe]

btrfs assigns this bdi to all inodes on that file system, so make
sure it's registered. This isn't really important now, but will be
when we put dirty inodes there. Even now, we miss the stats when the
bdi isn't visible.

Also fixes failure to check bdi_init() return value, and bad inherit of
->capabilities flags from the default bdi.

Acked-by: Chris Mason <chris.mason@oracle.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 fs/btrfs/disk-io.c |   26 +++++++++++++++++++++-----
 1 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 0d50d49..d28d29c 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -42,6 +42,8 @@
 static struct extent_io_ops btree_extent_io_ops;
 static void end_workqueue_fn(struct btrfs_work *work);
 
+static atomic_t btrfs_bdi_num = ATOMIC_INIT(0);
+
 /*
  * end_io_wq structs are used to do processing in task context when an IO is
  * complete.  This is used during reads to verify checksums, and it is used
@@ -1342,12 +1344,25 @@ static void btrfs_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
 	free_extent_map(em);
 }
 
+/*
+ * If this fails, caller must call bdi_destroy() to get rid of the
+ * bdi again.
+ */
 static int setup_bdi(struct btrfs_fs_info *info, struct backing_dev_info *bdi)
 {
-	bdi_init(bdi);
+	int err;
+
+	bdi->capabilities = BDI_CAP_MAP_COPY;
+	err = bdi_init(bdi);
+	if (err)
+		return err;
+
+	err = bdi_register(bdi, NULL, "btrfs-%d",
+				atomic_inc_return(&btrfs_bdi_num));
+	if (err)
+		return err;
+
 	bdi->ra_pages	= default_backing_dev_info.ra_pages;
-	bdi->state		= 0;
-	bdi->capabilities	= default_backing_dev_info.capabilities;
 	bdi->unplug_io_fn	= btrfs_unplug_io_fn;
 	bdi->unplug_io_data	= info;
 	bdi->congested_fn	= btrfs_congested_fn;
@@ -1569,7 +1584,8 @@ struct btrfs_root *open_ctree(struct super_block *sb,
 	fs_info->sb = sb;
 	fs_info->max_extent = (u64)-1;
 	fs_info->max_inline = 8192 * 1024;
-	setup_bdi(fs_info, &fs_info->bdi);
+	if (setup_bdi(fs_info, &fs_info->bdi))
+		goto fail_bdi;
 	fs_info->btree_inode = new_inode(sb);
 	fs_info->btree_inode->i_ino = 1;
 	fs_info->btree_inode->i_nlink = 1;
@@ -1946,8 +1962,8 @@ fail_iput:
 
 	btrfs_close_devices(fs_info->fs_devices);
 	btrfs_mapping_tree_free(&fs_info->mapping_tree);
+fail_bdi:
 	bdi_destroy(&fs_info->bdi);
-
 fail:
 	kfree(extent_root);
 	kfree(tree_root);
-- 
1.6.3.rc0.1.gf800

[PATCH 03/15] ubifs: register backing_dev_info

[Jens Axboe]

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 fs/ubifs/super.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/fs/ubifs/super.c b/fs/ubifs/super.c
index 3589eab..3260b73 100644
--- a/fs/ubifs/super.c
+++ b/fs/ubifs/super.c
@@ -1937,6 +1937,9 @@ static int ubifs_fill_super(struct super_block *sb, void *data, int silent)
 	err  = bdi_init(&c->bdi);
 	if (err)
 		goto out_close;
+	err = bdi_register(&c->bdi, NULL, "ubifs");
+	if (err)
+		goto out_bdi;
 
 	err = ubifs_parse_options(c, data, 0);
 	if (err)
-- 
1.6.3.rc0.1.gf800

[PATCH 04/15] writeback: move dirty inodes from super_block to backing_dev_info

[Jens Axboe]

This is a first step at introducing per-bdi flusher threads. We should
have no change in behaviour, although sb_has_dirty_inodes() is now
ridiculously expensive, as there's no easy way to answer that question.
Not a huge problem, since it'll be deleted in subsequent patches.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 fs/fs-writeback.c           |  196 +++++++++++++++++++++++++++---------------
 fs/super.c                  |    3 -
 include/linux/backing-dev.h |    9 ++
 include/linux/fs.h          |    5 +-
 mm/backing-dev.c            |   24 +++++
 mm/page-writeback.c         |   11 +--
 6 files changed, 164 insertions(+), 84 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 40308e9..7b01a34 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -25,6 +25,7 @@
 #include <linux/buffer_head.h>
 #include "internal.h"
 
+#define inode_to_bdi(inode)	((inode)->i_mapping->backing_dev_info)
 
 /**
  * writeback_acquire - attempt to get exclusive writeback access to a device
@@ -165,12 +166,13 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 			goto out;
 
 		/*
-		 * If the inode was already on s_dirty/s_io/s_more_io, don't
-		 * reposition it (that would break s_dirty time-ordering).
+		 * If the inode was already on b_dirty/b_io/b_more_io, don't
+		 * reposition it (that would break b_dirty time-ordering).
 		 */
 		if (!was_dirty) {
 			inode->dirtied_when = jiffies;
-			list_move(&inode->i_list, &sb->s_dirty);
+			list_move(&inode->i_list,
+					&inode_to_bdi(inode)->b_dirty);
 		}
 	}
 out:
@@ -191,31 +193,30 @@ static int write_inode(struct inode *inode, int sync)
  * furthest end of its superblock's dirty-inode list.
  *
  * Before stamping the inode's ->dirtied_when, we check to see whether it is
- * already the most-recently-dirtied inode on the s_dirty list.  If that is
+ * already the most-recently-dirtied inode on the b_dirty list.  If that is
  * the case then the inode must have been redirtied while it was being written
  * out and we don't reset its dirtied_when.
  */
 static void redirty_tail(struct inode *inode)
 {
-	struct super_block *sb = inode->i_sb;
+	struct backing_dev_info *bdi = inode_to_bdi(inode);
 
-	if (!list_empty(&sb->s_dirty)) {
-		struct inode *tail_inode;
+	if (!list_empty(&bdi->b_dirty)) {
+		struct inode *tail;
 
-		tail_inode = list_entry(sb->s_dirty.next, struct inode, i_list);
-		if (time_before(inode->dirtied_when,
-				tail_inode->dirtied_when))
+		tail = list_entry(bdi->b_dirty.next, struct inode, i_list);
+		if (time_before(inode->dirtied_when, tail->dirtied_when))
 			inode->dirtied_when = jiffies;
 	}
-	list_move(&inode->i_list, &sb->s_dirty);
+	list_move(&inode->i_list, &bdi->b_dirty);
 }
 
 /*
- * requeue inode for re-scanning after sb->s_io list is exhausted.
+ * requeue inode for re-scanning after bdi->b_io list is exhausted.
  */
 static void requeue_io(struct inode *inode)
 {
-	list_move(&inode->i_list, &inode->i_sb->s_more_io);
+	list_move(&inode->i_list, &inode_to_bdi(inode)->b_more_io);
 }
 
 static void inode_sync_complete(struct inode *inode)
@@ -262,18 +263,50 @@ static void move_expired_inodes(struct list_head *delaying_queue,
 /*
  * Queue all expired dirty inodes for io, eldest first.
  */
-static void queue_io(struct super_block *sb,
-				unsigned long *older_than_this)
+static void queue_io(struct backing_dev_info *bdi,
+		     unsigned long *older_than_this)
+{
+	list_splice_init(&bdi->b_more_io, bdi->b_io.prev);
+	move_expired_inodes(&bdi->b_dirty, &bdi->b_io, older_than_this);
+}
+
+static int sb_on_inode_list(struct super_block *sb, struct list_head *list)
 {
-	list_splice_init(&sb->s_more_io, sb->s_io.prev);
-	move_expired_inodes(&sb->s_dirty, &sb->s_io, older_than_this);
+	struct inode *inode;
+	int ret = 0;
+
+	spin_lock(&inode_lock);
+	list_for_each_entry(inode, list, i_list) {
+		if (inode->i_sb == sb) {
+			ret = 1;
+			break;
+		}
+	}
+	spin_unlock(&inode_lock);
+	return ret;
 }
 
 int sb_has_dirty_inodes(struct super_block *sb)
 {
-	return !list_empty(&sb->s_dirty) ||
-	       !list_empty(&sb->s_io) ||
-	       !list_empty(&sb->s_more_io);
+	struct backing_dev_info *bdi;
+	int ret = 0;
+
+	/*
+	 * This is REALLY expensive right now, but it'll go away
+	 * when the bdi writeback is introduced
+	 */
+	mutex_lock(&bdi_lock);
+	list_for_each_entry(bdi, &bdi_list, bdi_list) {
+		if (sb_on_inode_list(sb, &bdi->b_dirty) ||
+		    sb_on_inode_list(sb, &bdi->b_io) ||
+		    sb_on_inode_list(sb, &bdi->b_more_io)) {
+			ret = 1;
+			break;
+		}
+	}
+	mutex_unlock(&bdi_lock);
+
+	return ret;
 }
 EXPORT_SYMBOL(sb_has_dirty_inodes);
 
@@ -327,11 +360,11 @@ __sync_single_inode(struct inode *inode, struct writeback_control *wbc)
 			/*
 			 * We didn't write back all the pages.  nfs_writepages()
 			 * sometimes bales out without doing anything. Redirty
-			 * the inode; Move it from s_io onto s_more_io/s_dirty.
+			 * the inode; Move it from b_io onto b_more_io/b_dirty.
 			 */
 			/*
 			 * akpm: if the caller was the kupdate function we put
-			 * this inode at the head of s_dirty so it gets first
+			 * this inode at the head of b_dirty so it gets first
 			 * consideration.  Otherwise, move it to the tail, for
 			 * the reasons described there.  I'm not really sure
 			 * how much sense this makes.  Presumably I had a good
@@ -341,7 +374,7 @@ __sync_single_inode(struct inode *inode, struct writeback_control *wbc)
 			if (wbc->for_kupdate) {
 				/*
 				 * For the kupdate function we move the inode
-				 * to s_more_io so it will get more writeout as
+				 * to b_more_io so it will get more writeout as
 				 * soon as the queue becomes uncongested.
 				 */
 				inode->i_state |= I_DIRTY_PAGES;
@@ -407,10 +440,10 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
 	if ((wbc->sync_mode != WB_SYNC_ALL) && (inode->i_state & I_SYNC)) {
 		/*
 		 * We're skipping this inode because it's locked, and we're not
-		 * doing writeback-for-data-integrity.  Move it to s_more_io so
-		 * that writeback can proceed with the other inodes on s_io.
+		 * doing writeback-for-data-integrity.  Move it to b_more_io so
+		 * that writeback can proceed with the other inodes on b_io.
 		 * We'll have another go at writing back this inode when we
-		 * completed a full scan of s_io.
+		 * completed a full scan of b_io.
 		 */
 		requeue_io(inode);
 		return 0;
@@ -433,51 +466,34 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
 	return __sync_single_inode(inode, wbc);
 }
 
-/*
- * Write out a superblock's list of dirty inodes.  A wait will be performed
- * upon no inodes, all inodes or the final one, depending upon sync_mode.
- *
- * If older_than_this is non-NULL, then only write out inodes which
- * had their first dirtying at a time earlier than *older_than_this.
- *
- * If we're a pdflush thread, then implement pdflush collision avoidance
- * against the entire list.
- *
- * If `bdi' is non-zero then we're being asked to writeback a specific queue.
- * This function assumes that the blockdev superblock's inodes are backed by
- * a variety of queues, so all inodes are searched.  For other superblocks,
- * assume that all inodes are backed by the same queue.
- *
- * FIXME: this linear search could get expensive with many fileystems.  But
- * how to fix?  We need to go from an address_space to all inodes which share
- * a queue with that address_space.  (Easy: have a global "dirty superblocks"
- * list).
- *
- * The inodes to be written are parked on sb->s_io.  They are moved back onto
- * sb->s_dirty as they are selected for writing.  This way, none can be missed
- * on the writer throttling path, and we get decent balancing between many
- * throttled threads: we don't want them all piling up on inode_sync_wait.
- */
-void generic_sync_sb_inodes(struct super_block *sb,
-				struct writeback_control *wbc)
+static void generic_sync_bdi_inodes(struct backing_dev_info *bdi,
+				    struct writeback_control *wbc,
+				    struct super_block *sb,
+				    int is_blkdev_sb)
 {
 	const unsigned long start = jiffies;	/* livelock avoidance */
-	int sync = wbc->sync_mode == WB_SYNC_ALL;
 
 	spin_lock(&inode_lock);
-	if (!wbc->for_kupdate || list_empty(&sb->s_io))
-		queue_io(sb, wbc->older_than_this);
 
-	while (!list_empty(&sb->s_io)) {
-		struct inode *inode = list_entry(sb->s_io.prev,
+	if (!wbc->for_kupdate || list_empty(&bdi->b_io))
+		queue_io(bdi, wbc->older_than_this);
+
+	while (!list_empty(&bdi->b_io)) {
+		struct inode *inode = list_entry(bdi->b_io.prev,
 						struct inode, i_list);
-		struct address_space *mapping = inode->i_mapping;
-		struct backing_dev_info *bdi = mapping->backing_dev_info;
 		long pages_skipped;
 
+		/*
+		 * super block given and doesn't match, skip this inode
+		 */
+		if (sb && sb != inode->i_sb) {
+			redirty_tail(inode);
+			continue;
+		}
+
 		if (!bdi_cap_writeback_dirty(bdi)) {
 			redirty_tail(inode);
-			if (sb_is_blkdev_sb(sb)) {
+			if (is_blkdev_sb) {
 				/*
 				 * Dirty memory-backed blockdev: the ramdisk
 				 * driver does this.  Skip just this inode
@@ -499,14 +515,14 @@ void generic_sync_sb_inodes(struct super_block *sb,
 
 		if (wbc->nonblocking && bdi_write_congested(bdi)) {
 			wbc->encountered_congestion = 1;
-			if (!sb_is_blkdev_sb(sb))
+			if (!is_blkdev_sb)
 				break;		/* Skip a congested fs */
 			requeue_io(inode);
 			continue;		/* Skip a congested blockdev */
 		}
 
 		if (wbc->bdi && bdi != wbc->bdi) {
-			if (!sb_is_blkdev_sb(sb))
+			if (!is_blkdev_sb)
 				break;		/* fs has the wrong queue */
 			requeue_io(inode);
 			continue;		/* blockdev has wrong queue */
@@ -544,13 +560,55 @@ void generic_sync_sb_inodes(struct super_block *sb,
 			wbc->more_io = 1;
 			break;
 		}
-		if (!list_empty(&sb->s_more_io))
+		if (!list_empty(&bdi->b_more_io))
 			wbc->more_io = 1;
 	}
 
-	if (sync) {
+	spin_unlock(&inode_lock);
+	/* Leave any unwritten inodes on b_io */
+}
+
+/*
+ * Write out a superblock's list of dirty inodes.  A wait will be performed
+ * upon no inodes, all inodes or the final one, depending upon sync_mode.
+ *
+ * If older_than_this is non-NULL, then only write out inodes which
+ * had their first dirtying at a time earlier than *older_than_this.
+ *
+ * If we're a pdlfush thread, then implement pdflush collision avoidance
+ * against the entire list.
+ *
+ * If `bdi' is non-zero then we're being asked to writeback a specific queue.
+ * This function assumes that the blockdev superblock's inodes are backed by
+ * a variety of queues, so all inodes are searched.  For other superblocks,
+ * assume that all inodes are backed by the same queue.
+ *
+ * FIXME: this linear search could get expensive with many fileystems.  But
+ * how to fix?  We need to go from an address_space to all inodes which share
+ * a queue with that address_space.  (Easy: have a global "dirty superblocks"
+ * list).
+ *
+ * The inodes to be written are parked on bdi->b_io.  They are moved back onto
+ * bdi->b_dirty as they are selected for writing.  This way, none can be missed
+ * on the writer throttling path, and we get decent balancing between many
+ * throttled threads: we don't want them all piling up on inode_sync_wait.
+ */
+void generic_sync_sb_inodes(struct super_block *sb,
+				struct writeback_control *wbc)
+{
+	const int is_blkdev_sb = sb_is_blkdev_sb(sb);
+	struct backing_dev_info *bdi;
+
+	mutex_lock(&bdi_lock);
+	list_for_each_entry(bdi, &bdi_list, bdi_list)
+		generic_sync_bdi_inodes(bdi, wbc, sb, is_blkdev_sb);
+	mutex_unlock(&bdi_lock);
+
+	if (wbc->sync_mode == WB_SYNC_ALL) {
 		struct inode *inode, *old_inode = NULL;
 
+		spin_lock(&inode_lock);
+
 		/*
 		 * Data integrity sync. Must wait for all pages under writeback,
 		 * because there may have been pages dirtied before our sync
@@ -588,10 +646,8 @@ void generic_sync_sb_inodes(struct super_block *sb,
 		}
 		spin_unlock(&inode_lock);
 		iput(old_inode);
-	} else
-		spin_unlock(&inode_lock);
+	}
 
-	return;		/* Leave any unwritten inodes on s_io */
 }
 EXPORT_SYMBOL_GPL(generic_sync_sb_inodes);
 
@@ -606,8 +662,8 @@ static void sync_sb_inodes(struct super_block *sb,
  *
  * Note:
  * We don't need to grab a reference to superblock here. If it has non-empty
- * ->s_dirty it's hadn't been killed yet and kill_super() won't proceed
- * past sync_inodes_sb() until the ->s_dirty/s_io/s_more_io lists are all
+ * ->b_dirty it's hadn't been killed yet and kill_super() won't proceed
+ * past sync_inodes_sb() until the ->b_dirty/b_io/b_more_io lists are all
  * empty. Since __sync_single_inode() regains inode_lock before it finally moves
  * inode from superblock lists we are OK.
  *
diff --git a/fs/super.c b/fs/super.c
index 83b4741..417c418 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -62,9 +62,6 @@ static struct super_block *alloc_super(struct file_system_type *type)
 			s = NULL;
 			goto out;
 		}
-		INIT_LIST_HEAD(&s->s_dirty);
-		INIT_LIST_HEAD(&s->s_io);
-		INIT_LIST_HEAD(&s->s_more_io);
 		INIT_LIST_HEAD(&s->s_files);
 		INIT_LIST_HEAD(&s->s_instances);
 		INIT_HLIST_HEAD(&s->s_anon);
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 0ec2c59..8719c87 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -40,6 +40,8 @@ enum bdi_stat_item {
 #define BDI_STAT_BATCH (8*(1+ilog2(nr_cpu_ids)))
 
 struct backing_dev_info {
+	struct list_head bdi_list;
+
 	unsigned long ra_pages;	/* max readahead in PAGE_CACHE_SIZE units */
 	unsigned long state;	/* Always use atomic bitops on this */
 	unsigned int capabilities; /* Device capabilities */
@@ -58,6 +60,10 @@ struct backing_dev_info {
 
 	struct device *dev;
 
+	struct list_head	b_dirty;	/* dirty inodes */
+	struct list_head	b_io;		/* parked for writeback */
+	struct list_head	b_more_io;	/* parked for more writeback */
+
 #ifdef CONFIG_DEBUG_FS
 	struct dentry *debug_dir;
 	struct dentry *debug_stats;
@@ -72,6 +78,9 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev);
 void bdi_unregister(struct backing_dev_info *bdi);
 
+extern struct mutex bdi_lock;
+extern struct list_head bdi_list;
+
 static inline void __add_bdi_stat(struct backing_dev_info *bdi,
 		enum bdi_stat_item item, s64 amount)
 {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index ede84fa..6e6046a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -712,7 +712,7 @@ static inline int mapping_writably_mapped(struct address_space *mapping)
 
 struct inode {
 	struct hlist_node	i_hash;
-	struct list_head	i_list;
+	struct list_head	i_list;		/* backing dev IO list */
 	struct list_head	i_sb_list;
 	struct list_head	i_dentry;
 	unsigned long		i_ino;
@@ -1328,9 +1328,6 @@ struct super_block {
 	struct xattr_handler	**s_xattr;
 
 	struct list_head	s_inodes;	/* all inodes */
-	struct list_head	s_dirty;	/* dirty inodes */
-	struct list_head	s_io;		/* parked for writeback */
-	struct list_head	s_more_io;	/* parked for more writeback */
 	struct hlist_head	s_anon;		/* anonymous dentries for (nfs) exporting */
 	struct list_head	s_files;
 	/* s_dentry_lru and s_nr_dentry_unused are protected by dcache_lock */
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 493b468..de0bbfe 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -22,6 +22,8 @@ struct backing_dev_info default_backing_dev_info = {
 EXPORT_SYMBOL_GPL(default_backing_dev_info);
 
 static struct class *bdi_class;
+DEFINE_MUTEX(bdi_lock);
+LIST_HEAD(bdi_list);
 
 #ifdef CONFIG_DEBUG_FS
 #include <linux/debugfs.h>
@@ -211,6 +213,10 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 		goto exit;
 	}
 
+	mutex_lock(&bdi_lock);
+	list_add_tail(&bdi->bdi_list, &bdi_list);
+	mutex_unlock(&bdi_lock);
+
 	bdi->dev = dev;
 	bdi_debug_register(bdi, dev_name(dev));
 
@@ -225,9 +231,17 @@ int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
 }
 EXPORT_SYMBOL(bdi_register_dev);
 
+static void bdi_remove_from_list(struct backing_dev_info *bdi)
+{
+	mutex_lock(&bdi_lock);
+	list_del(&bdi->bdi_list);
+	mutex_unlock(&bdi_lock);
+}
+
 void bdi_unregister(struct backing_dev_info *bdi)
 {
 	if (bdi->dev) {
+		bdi_remove_from_list(bdi);
 		bdi_debug_unregister(bdi);
 		device_unregister(bdi->dev);
 		bdi->dev = NULL;
@@ -245,6 +259,10 @@ int bdi_init(struct backing_dev_info *bdi)
 	bdi->min_ratio = 0;
 	bdi->max_ratio = 100;
 	bdi->max_prop_frac = PROP_FRAC_BASE;
+	INIT_LIST_HEAD(&bdi->bdi_list);
+	INIT_LIST_HEAD(&bdi->b_io);
+	INIT_LIST_HEAD(&bdi->b_dirty);
+	INIT_LIST_HEAD(&bdi->b_more_io);
 
 	for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
 		err = percpu_counter_init(&bdi->bdi_stat[i], 0);
@@ -259,6 +277,8 @@ int bdi_init(struct backing_dev_info *bdi)
 err:
 		while (i--)
 			percpu_counter_destroy(&bdi->bdi_stat[i]);
+
+		bdi_remove_from_list(bdi);
 	}
 
 	return err;
@@ -269,6 +289,10 @@ void bdi_destroy(struct backing_dev_info *bdi)
 {
 	int i;
 
+	WARN_ON(!list_empty(&bdi->b_dirty));
+	WARN_ON(!list_empty(&bdi->b_io));
+	WARN_ON(!list_empty(&bdi->b_more_io));
+
 	bdi_unregister(bdi);
 
 	for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index bb553c3..7c44314 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -319,15 +319,13 @@ static void task_dirty_limit(struct task_struct *tsk, long *pdirty)
 /*
  *
  */
-static DEFINE_SPINLOCK(bdi_lock);
 static unsigned int bdi_min_ratio;
 
 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
 {
 	int ret = 0;
-	unsigned long flags;
 
-	spin_lock_irqsave(&bdi_lock, flags);
+	mutex_lock(&bdi_lock);
 	if (min_ratio > bdi->max_ratio) {
 		ret = -EINVAL;
 	} else {
@@ -339,27 +337,26 @@ int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
 			ret = -EINVAL;
 		}
 	}
-	spin_unlock_irqrestore(&bdi_lock, flags);
+	mutex_unlock(&bdi_lock);
 
 	return ret;
 }
 
 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
 {
-	unsigned long flags;
 	int ret = 0;
 
 	if (max_ratio > 100)
 		return -EINVAL;
 
-	spin_lock_irqsave(&bdi_lock, flags);
+	mutex_lock(&bdi_lock);
 	if (bdi->min_ratio > max_ratio) {
 		ret = -EINVAL;
 	} else {
 		bdi->max_ratio = max_ratio;
 		bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
 	}
-	spin_unlock_irqrestore(&bdi_lock, flags);
+	mutex_unlock(&bdi_lock);
 
 	return ret;
 }
-- 
1.6.3.rc0.1.gf800

[PATCH 05/15] writeback: switch to per-bdi threads for flushing data

[Jens Axboe]

This gets rid of pdflush for bdi writeout and kupdated style cleaning.
This is an experiment to see if we get better writeout behaviour with
per-bdi flushing. Some initial tests look pretty encouraging. A sample
ffsb workload that does random writes to files is about 8% faster here
on a simple SATA drive during the benchmark phase. File layout also seems
a LOT more smooth in vmstat:

 r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id wa
 0  1      0 608848   2652 375372    0    0     0 71024  604    24  1 10 48 42
 0  1      0 549644   2712 433736    0    0     0 60692  505    27  1  8 48 44
 1  0      0 476928   2784 505192    0    0     4 29540  553    24  0  9 53 37
 0  1      0 457972   2808 524008    0    0     0 54876  331    16  0  4 38 58
 0  1      0 366128   2928 614284    0    0     4 92168  710    58  0 13 53 34
 0  1      0 295092   3000 684140    0    0     0 62924  572    23  0  9 53 37
 0  1      0 236592   3064 741704    0    0     4 58256  523    17  0  8 48 44
 0  1      0 165608   3132 811464    0    0     0 57460  560    21  0  8 54 38
 0  1      0 102952   3200 873164    0    0     4 74748  540    29  1 10 48 41
 0  1      0  48604   3252 926472    0    0     0 53248  469    29  0  7 47 45

where vanilla tends to fluctuate a lot in the creation phase:

 r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id wa
 1  1      0 678716   5792 303380    0    0     0 74064  565    50  1 11 52 36
 1  0      0 662488   5864 319396    0    0     4   352  302   329  0  2 47 51
 0  1      0 599312   5924 381468    0    0     0 78164  516    55  0  9 51 40
 0  1      0 519952   6008 459516    0    0     4 78156  622    56  1 11 52 37
 1  1      0 436640   6092 541632    0    0     0 82244  622    54  0 11 48 41
 0  1      0 436640   6092 541660    0    0     0     8  152    39  0  0 51 49
 0  1      0 332224   6200 644252    0    0     4 102800  728    46  1 13 49 36
 1  0      0 274492   6260 701056    0    0     4 12328  459    49  0  7 50 43
 0  1      0 211220   6324 763356    0    0     0 106940  515    37  1 10 51 39
 1  0      0 160412   6376 813468    0    0     0  8224  415    43  0  6 49 45
 1  1      0  85980   6452 886556    0    0     4 113516  575    39  1 11 54 34
 0  2      0  85968   6452 886620    0    0     0  1640  158   211  0  0 46 54

So apart from seemingly behaving better for buffered writeout, this also
allows us to potentially have more than one bdi thread flushing out data.
This may be useful for NUMA type setups.

A 10 disk test with btrfs performs 26% faster with per-bdi flushing. Other
tests pending. mmap heavy writing also improves considerably.

A separate thread is added to sync the super blocks. In the long term,
adding sync_supers_bdi() functionality could get rid of this thread again.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 fs/buffer.c                 |    2 +-
 fs/fs-writeback.c           |  309 ++++++++++++++++++++++++++-----------------
 include/linux/backing-dev.h |   27 ++++
 include/linux/fs.h          |    3 +-
 include/linux/writeback.h   |    2 +-
 mm/backing-dev.c            |  232 +++++++++++++++++++++++++++++++-
 mm/page-writeback.c         |  146 +++------------------
 mm/vmscan.c                 |    2 +-
 8 files changed, 461 insertions(+), 262 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index a3ef091..2a01b2b 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -281,7 +281,7 @@ static void free_more_memory(void)
 	struct zone *zone;
 	int nid;
 
-	wakeup_pdflush(1024);
+	wakeup_flusher_threads(1024);
 	yield();
 
 	for_each_online_node(nid) {
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 7b01a34..f7a5e39 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -19,6 +19,8 @@
 #include <linux/sched.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
+#include <linux/kthread.h>
+#include <linux/freezer.h>
 #include <linux/writeback.h>
 #include <linux/blkdev.h>
 #include <linux/backing-dev.h>
@@ -61,10 +63,186 @@ int writeback_in_progress(struct backing_dev_info *bdi)
  */
 static void writeback_release(struct backing_dev_info *bdi)
 {
-	BUG_ON(!writeback_in_progress(bdi));
+	WARN_ON_ONCE(!writeback_in_progress(bdi));
+	bdi->wb_arg.nr_pages = 0;
+	bdi->wb_arg.sb = NULL;
 	clear_bit(BDI_pdflush, &bdi->state);
 }
 
+int bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
+			 long nr_pages, enum writeback_sync_modes sync_mode)
+{
+	/*
+	 * This only happens the first time someone kicks this bdi, so put
+	 * it out-of-line.
+	 */
+	if (unlikely(!bdi->task)) {
+		bdi_add_default_flusher_task(bdi);
+		return 1;
+	}
+
+	if (writeback_acquire(bdi)) {
+		bdi->wb_arg.nr_pages = nr_pages;
+		bdi->wb_arg.sb = sb;
+		bdi->wb_arg.sync_mode = sync_mode;
+
+		if (bdi->task)
+			wake_up_process(bdi->task);
+	}
+
+	return 0;
+}
+
+/*
+ * The maximum number of pages to writeout in a single bdi flush/kupdate
+ * operation.  We do this so we don't hold I_SYNC 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
+
+/*
+ * 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_interval.  But if a writeback event
+ * takes longer than a dirty_writeback_interval 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 bdi_kupdated(struct backing_dev_info *bdi)
+{
+	unsigned long oldest_jif;
+	long nr_to_write;
+	struct writeback_control wbc = {
+		.bdi			= bdi,
+		.sync_mode		= WB_SYNC_NONE,
+		.older_than_this	= &oldest_jif,
+		.nr_to_write		= 0,
+		.for_kupdate		= 1,
+		.range_cyclic		= 1,
+	};
+
+	oldest_jif = jiffies - msecs_to_jiffies(dirty_expire_interval * 10);
+
+	nr_to_write = global_page_state(NR_FILE_DIRTY) +
+			global_page_state(NR_UNSTABLE_NFS) +
+			(inodes_stat.nr_inodes - inodes_stat.nr_unused);
+
+	while (nr_to_write > 0) {
+		wbc.more_io = 0;
+		wbc.encountered_congestion = 0;
+		wbc.nr_to_write = MAX_WRITEBACK_PAGES;
+		generic_sync_bdi_inodes(NULL, &wbc);
+		if (wbc.nr_to_write > 0)
+			break;	/* All the old data is written */
+		nr_to_write -= MAX_WRITEBACK_PAGES;
+	}
+}
+
+static inline bool over_bground_thresh(void)
+{
+	unsigned long background_thresh, dirty_thresh;
+
+	get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
+
+	return (global_page_state(NR_FILE_DIRTY) +
+		global_page_state(NR_UNSTABLE_NFS) >= background_thresh);
+}
+
+static void bdi_pdflush(struct backing_dev_info *bdi)
+{
+	struct writeback_control wbc = {
+		.bdi			= bdi,
+		.sync_mode		= bdi->wb_arg.sync_mode,
+		.older_than_this	= NULL,
+		.range_cyclic		= 1,
+	};
+	long nr_pages = bdi->wb_arg.nr_pages;
+
+	for (;;) {
+		if (wbc.sync_mode == WB_SYNC_NONE && nr_pages <= 0 &&
+		    !over_bground_thresh())
+			break;
+
+		wbc.more_io = 0;
+		wbc.encountered_congestion = 0;
+		wbc.nr_to_write = MAX_WRITEBACK_PAGES;
+		wbc.pages_skipped = 0;
+		generic_sync_bdi_inodes(bdi->wb_arg.sb, &wbc);
+		nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
+		/*
+		 * If we ran out of stuff to write, bail unless more_io got set
+		 */
+		if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
+			if (wbc.more_io)
+				continue;
+			break;
+		}
+	}
+}
+
+/*
+ * Handle writeback of dirty data for the device backed by this bdi. Also
+ * wakes up periodically and does kupdated style flushing.
+ */
+int bdi_writeback_task(struct backing_dev_info *bdi)
+{
+	while (!kthread_should_stop()) {
+		unsigned long wait_jiffies;
+
+		wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10);
+		set_current_state(TASK_INTERRUPTIBLE);
+		schedule_timeout(wait_jiffies);
+		try_to_freeze();
+
+		/*
+		 * We get here in two cases:
+		 *
+		 *  schedule_timeout() returned because the dirty writeback
+		 *  interval has elapsed. If that happens, we will be able
+		 *  to acquire the writeback lock and will proceed to do
+		 *  kupdated style writeout.
+		 *
+		 *  Someone called bdi_start_writeback(), which will acquire
+		 *  the writeback lock. This means our writeback_acquire()
+		 *  below will fail and we call into bdi_pdflush() for
+		 *  pdflush style writeout.
+		 *
+		 */
+		if (writeback_acquire(bdi))
+			bdi_kupdated(bdi);
+		else
+			bdi_pdflush(bdi);
+
+		writeback_release(bdi);
+	}
+
+	return 0;
+}
+
+void bdi_writeback_all(struct super_block *sb, struct writeback_control *wbc)
+{
+	struct backing_dev_info *bdi, *tmp;
+
+	mutex_lock(&bdi_lock);
+
+	list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
+		if (!bdi_has_dirty_io(bdi))
+			continue;
+		bdi_start_writeback(bdi, sb, wbc->nr_to_write, wbc->sync_mode);
+	}
+
+	mutex_unlock(&bdi_lock);
+}
+
 static noinline void block_dump___mark_inode_dirty(struct inode *inode)
 {
 	if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
@@ -270,46 +448,6 @@ static void queue_io(struct backing_dev_info *bdi,
 	move_expired_inodes(&bdi->b_dirty, &bdi->b_io, older_than_this);
 }
 
-static int sb_on_inode_list(struct super_block *sb, struct list_head *list)
-{
-	struct inode *inode;
-	int ret = 0;
-
-	spin_lock(&inode_lock);
-	list_for_each_entry(inode, list, i_list) {
-		if (inode->i_sb == sb) {
-			ret = 1;
-			break;
-		}
-	}
-	spin_unlock(&inode_lock);
-	return ret;
-}
-
-int sb_has_dirty_inodes(struct super_block *sb)
-{
-	struct backing_dev_info *bdi;
-	int ret = 0;
-
-	/*
-	 * This is REALLY expensive right now, but it'll go away
-	 * when the bdi writeback is introduced
-	 */
-	mutex_lock(&bdi_lock);
-	list_for_each_entry(bdi, &bdi_list, bdi_list) {
-		if (sb_on_inode_list(sb, &bdi->b_dirty) ||
-		    sb_on_inode_list(sb, &bdi->b_io) ||
-		    sb_on_inode_list(sb, &bdi->b_more_io)) {
-			ret = 1;
-			break;
-		}
-	}
-	mutex_unlock(&bdi_lock);
-
-	return ret;
-}
-EXPORT_SYMBOL(sb_has_dirty_inodes);
-
 /*
  * Write a single inode's dirty pages and inode data out to disk.
  * If `wait' is set, wait on the writeout.
@@ -466,11 +604,11 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
 	return __sync_single_inode(inode, wbc);
 }
 
-static void generic_sync_bdi_inodes(struct backing_dev_info *bdi,
-				    struct writeback_control *wbc,
-				    struct super_block *sb,
-				    int is_blkdev_sb)
+void generic_sync_bdi_inodes(struct super_block *sb,
+			     struct writeback_control *wbc)
 {
+	const int is_blkdev_sb = sb_is_blkdev_sb(sb);
+	struct backing_dev_info *bdi = wbc->bdi;
 	const unsigned long start = jiffies;	/* livelock avoidance */
 
 	spin_lock(&inode_lock);
@@ -521,13 +659,6 @@ static void generic_sync_bdi_inodes(struct backing_dev_info *bdi,
 			continue;		/* Skip a congested blockdev */
 		}
 
-		if (wbc->bdi && bdi != wbc->bdi) {
-			if (!is_blkdev_sb)
-				break;		/* fs has the wrong queue */
-			requeue_io(inode);
-			continue;		/* blockdev has wrong queue */
-		}
-
 		/*
 		 * Was this inode dirtied after sync_sb_inodes was called?
 		 * This keeps sync from extra jobs and livelock.
@@ -535,16 +666,10 @@ static void generic_sync_bdi_inodes(struct backing_dev_info *bdi,
 		if (inode_dirtied_after(inode, start))
 			break;
 
-		/* Is another pdflush already flushing this queue? */
-		if (current_is_pdflush() && !writeback_acquire(bdi))
-			break;
-
 		BUG_ON(inode->i_state & I_FREEING);
 		__iget(inode);
 		pages_skipped = wbc->pages_skipped;
 		__writeback_single_inode(inode, wbc);
-		if (current_is_pdflush())
-			writeback_release(bdi);
 		if (wbc->pages_skipped != pages_skipped) {
 			/*
 			 * writeback is not making progress due to locked
@@ -583,11 +708,6 @@ static void generic_sync_bdi_inodes(struct backing_dev_info *bdi,
  * a variety of queues, so all inodes are searched.  For other superblocks,
  * assume that all inodes are backed by the same queue.
  *
- * FIXME: this linear search could get expensive with many fileystems.  But
- * how to fix?  We need to go from an address_space to all inodes which share
- * a queue with that address_space.  (Easy: have a global "dirty superblocks"
- * list).
- *
  * The inodes to be written are parked on bdi->b_io.  They are moved back onto
  * bdi->b_dirty as they are selected for writing.  This way, none can be missed
  * on the writer throttling path, and we get decent balancing between many
@@ -596,13 +716,10 @@ static void generic_sync_bdi_inodes(struct backing_dev_info *bdi,
 void generic_sync_sb_inodes(struct super_block *sb,
 				struct writeback_control *wbc)
 {
-	const int is_blkdev_sb = sb_is_blkdev_sb(sb);
-	struct backing_dev_info *bdi;
-
-	mutex_lock(&bdi_lock);
-	list_for_each_entry(bdi, &bdi_list, bdi_list)
-		generic_sync_bdi_inodes(bdi, wbc, sb, is_blkdev_sb);
-	mutex_unlock(&bdi_lock);
+	if (wbc->bdi)
+		generic_sync_bdi_inodes(sb, wbc);
+	else
+		bdi_writeback_all(sb, wbc);
 
 	if (wbc->sync_mode == WB_SYNC_ALL) {
 		struct inode *inode, *old_inode = NULL;
@@ -658,58 +775,6 @@ static void sync_sb_inodes(struct super_block *sb,
 }
 
 /*
- * Start writeback of dirty pagecache data against all unlocked inodes.
- *
- * Note:
- * We don't need to grab a reference to superblock here. If it has non-empty
- * ->b_dirty it's hadn't been killed yet and kill_super() won't proceed
- * past sync_inodes_sb() until the ->b_dirty/b_io/b_more_io lists are all
- * empty. Since __sync_single_inode() regains inode_lock before it finally moves
- * inode from superblock lists we are OK.
- *
- * If `older_than_this' is non-zero then only flush inodes which have a
- * flushtime older than *older_than_this.
- *
- * If `bdi' is non-zero then we will scan the first inode against each
- * superblock until we find the matching ones.  One group will be the dirty
- * inodes against a filesystem.  Then when we hit the dummy blockdev superblock,
- * sync_sb_inodes will seekout the blockdev which matches `bdi'.  Maybe not
- * super-efficient but we're about to do a ton of I/O...
- */
-void
-writeback_inodes(struct writeback_control *wbc)
-{
-	struct super_block *sb;
-
-	might_sleep();
-	spin_lock(&sb_lock);
-restart:
-	list_for_each_entry_reverse(sb, &super_blocks, s_list) {
-		if (sb_has_dirty_inodes(sb)) {
-			/* we're making our own get_super here */
-			sb->s_count++;
-			spin_unlock(&sb_lock);
-			/*
-			 * If we can't get the readlock, there's no sense in
-			 * waiting around, most of the time the FS is going to
-			 * be unmounted by the time it is released.
-			 */
-			if (down_read_trylock(&sb->s_umount)) {
-				if (sb->s_root)
-					sync_sb_inodes(sb, wbc);
-				up_read(&sb->s_umount);
-			}
-			spin_lock(&sb_lock);
-			if (__put_super_and_need_restart(sb))
-				goto restart;
-		}
-		if (wbc->nr_to_write <= 0)
-			break;
-	}
-	spin_unlock(&sb_lock);
-}
-
-/*
  * writeback and wait upon the filesystem's dirty inodes.  The caller will
  * do this in two passes - one to write, and one to wait.
  *
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 8719c87..12e387b 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -13,6 +13,7 @@
 #include <linux/proportions.h>
 #include <linux/kernel.h>
 #include <linux/fs.h>
+#include <linux/writeback.h>
 #include <asm/atomic.h>
 
 struct page;
@@ -24,6 +25,7 @@ struct dentry;
  */
 enum bdi_state {
 	BDI_pdflush,		/* A pdflush thread is working this device */
+	BDI_pending,		/* On its way to being activated */
 	BDI_async_congested,	/* The async (write) queue is getting full */
 	BDI_sync_congested,	/* The sync queue is getting full */
 	BDI_unused,		/* Available bits start here */
@@ -39,6 +41,12 @@ enum bdi_stat_item {
 
 #define BDI_STAT_BATCH (8*(1+ilog2(nr_cpu_ids)))
 
+struct bdi_writeback_arg {
+	unsigned long nr_pages;
+	struct super_block *sb;
+	enum writeback_sync_modes sync_mode;
+};
+
 struct backing_dev_info {
 	struct list_head bdi_list;
 
@@ -60,6 +68,8 @@ struct backing_dev_info {
 
 	struct device *dev;
 
+	struct task_struct	*task;		/* writeback task */
+	struct bdi_writeback_arg wb_arg;	/* protected by BDI_pdflush */
 	struct list_head	b_dirty;	/* dirty inodes */
 	struct list_head	b_io;		/* parked for writeback */
 	struct list_head	b_more_io;	/* parked for more writeback */
@@ -77,10 +87,22 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 		const char *fmt, ...);
 int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev);
 void bdi_unregister(struct backing_dev_info *bdi);
+int bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
+			 long nr_pages, enum writeback_sync_modes sync_mode);
+int bdi_writeback_task(struct backing_dev_info *bdi);
+void bdi_writeback_all(struct super_block *sb, struct writeback_control *wbc);
+void bdi_add_default_flusher_task(struct backing_dev_info *bdi);
 
 extern struct mutex bdi_lock;
 extern struct list_head bdi_list;
 
+static inline int bdi_has_dirty_io(struct backing_dev_info *bdi)
+{
+	return !list_empty(&bdi->b_dirty) ||
+	       !list_empty(&bdi->b_io) ||
+	       !list_empty(&bdi->b_more_io);
+}
+
 static inline void __add_bdi_stat(struct backing_dev_info *bdi,
 		enum bdi_stat_item item, s64 amount)
 {
@@ -265,6 +287,11 @@ static inline bool bdi_cap_swap_backed(struct backing_dev_info *bdi)
 	return bdi->capabilities & BDI_CAP_SWAP_BACKED;
 }
 
+static inline bool bdi_cap_flush_forker(struct backing_dev_info *bdi)
+{
+	return bdi == &default_backing_dev_info;
+}
+
 static inline bool mapping_cap_writeback_dirty(struct address_space *mapping)
 {
 	return bdi_cap_writeback_dirty(mapping->backing_dev_info);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 6e6046a..1a8fe89 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2056,6 +2056,8 @@ extern int invalidate_inode_pages2_range(struct address_space *mapping,
 					 pgoff_t start, pgoff_t end);
 extern void generic_sync_sb_inodes(struct super_block *sb,
 				struct writeback_control *wbc);
+extern void generic_sync_bdi_inodes(struct super_block *sb,
+				struct writeback_control *);
 extern int write_inode_now(struct inode *, int);
 extern int filemap_fdatawrite(struct address_space *);
 extern int filemap_flush(struct address_space *);
@@ -2169,7 +2171,6 @@ extern int bdev_read_only(struct block_device *);
 extern int set_blocksize(struct block_device *, int);
 extern int sb_set_blocksize(struct super_block *, int);
 extern int sb_min_blocksize(struct super_block *, int);
-extern int sb_has_dirty_inodes(struct super_block *);
 
 extern int generic_file_mmap(struct file *, struct vm_area_struct *);
 extern int generic_file_readonly_mmap(struct file *, struct vm_area_struct *);
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 3224820..6999882 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -98,7 +98,7 @@ static inline void inode_sync_wait(struct inode *inode)
 /*
  * mm/page-writeback.c
  */
-int wakeup_pdflush(long nr_pages);
+void wakeup_flusher_threads(long nr_pages);
 void laptop_io_completion(void);
 void laptop_sync_completion(void);
 void throttle_vm_writeout(gfp_t gfp_mask);
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index de0bbfe..c620c93 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -1,8 +1,11 @@
 
 #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>
@@ -24,6 +27,14 @@ EXPORT_SYMBOL_GPL(default_backing_dev_info);
 static struct class *bdi_class;
 DEFINE_MUTEX(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);
+static void arm_supers_timer(void);
 
 #ifdef CONFIG_DEBUG_FS
 #include <linux/debugfs.h>
@@ -187,6 +198,13 @@ static int __init default_bdi_init(void)
 {
 	int err;
 
+	sync_supers_tsk = kthread_run(bdi_sync_supers, NULL, "sync_supers");
+	BUG_ON(!sync_supers_tsk);
+
+	init_timer(&sync_supers_timer);
+	setup_timer(&sync_supers_timer, sync_supers_timer_fn, 0);
+	arm_supers_timer();
+
 	err = bdi_init(&default_backing_dev_info);
 	if (!err)
 		bdi_register(&default_backing_dev_info, NULL, "default");
@@ -195,6 +213,175 @@ static int __init default_bdi_init(void)
 }
 subsys_initcall(default_bdi_init);
 
+static int bdi_start_fn(void *ptr)
+{
+	struct backing_dev_info *bdi = ptr;
+	struct task_struct *tsk = current;
+
+	/*
+	 * Add us to the active bdi_list
+	 */
+	mutex_lock(&bdi_lock);
+	list_add(&bdi->bdi_list, &bdi_list);
+	mutex_unlock(&bdi_lock);
+
+	tsk->flags |= PF_FLUSHER | PF_SWAPWRITE;
+	set_freezable();
+
+	/*
+	 * Our parent may run at a different priority, just set us to normal
+	 */
+	set_user_nice(tsk, 0);
+
+	/*
+	 * Clear pending bit and wakeup anybody waiting to tear us down
+	 */
+	clear_bit(BDI_pending, &bdi->state);
+	smp_mb__after_clear_bit();
+	wake_up_bit(&bdi->state, BDI_pending);
+
+	return bdi_writeback_task(bdi);
+}
+
+static void bdi_flush_io(struct backing_dev_info *bdi)
+{
+	struct writeback_control wbc = {
+		.bdi			= bdi,
+		.sync_mode		= WB_SYNC_NONE,
+		.older_than_this	= NULL,
+		.range_cyclic		= 1,
+		.nr_to_write		= 1024,
+	};
+
+	generic_sync_bdi_inodes(NULL, &wbc);
+}
+
+/*
+ * kupdated() used to do this. We cannot do it from the bdi_forker_task()
+ * 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 tasks 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;
+}
+
+static void arm_supers_timer(void)
+{
+	unsigned long next;
+
+	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);
+	arm_supers_timer();
+}
+
+static int bdi_forker_task(void *ptr)
+{
+	struct backing_dev_info *me = ptr;
+
+	for (;;) {
+		struct backing_dev_info *bdi, *tmp;
+
+		/*
+		 * Temporary measure, we want to make sure we don't see
+		 * dirty data on the default backing_dev_info
+		 */
+		if (bdi_has_dirty_io(me))
+			bdi_flush_io(me);
+
+		mutex_lock(&bdi_lock);
+
+		/*
+		 * Check if any existing bdi's have dirty data without
+		 * a thread registered. If so, set that up.
+		 */
+		list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
+			if (bdi->task || !bdi_has_dirty_io(bdi))
+				continue;
+
+			bdi_add_default_flusher_task(bdi);
+		}
+
+		set_current_state(TASK_INTERRUPTIBLE);
+
+		if (list_empty(&bdi_pending_list)) {
+			unsigned long wait;
+
+			mutex_unlock(&bdi_lock);
+			wait = msecs_to_jiffies(dirty_writeback_interval * 10);
+			schedule_timeout(wait);
+			try_to_freeze();
+			continue;
+		}
+
+		__set_current_state(TASK_RUNNING);
+
+		/*
+		 * This is our real job - check for pending entries in
+		 * bdi_pending_list, and create the tasks that got added
+		 */
+		bdi = list_entry(bdi_pending_list.next, struct backing_dev_info,
+				 bdi_list);
+		list_del_init(&bdi->bdi_list);
+		mutex_unlock(&bdi_lock);
+
+		BUG_ON(bdi->task);
+
+		bdi->task = kthread_run(bdi_start_fn, bdi, "flush-%s",
+					dev_name(bdi->dev));
+		/*
+		 * If task creation fails, then readd the bdi to
+		 * the pending list and force writeout of the bdi
+		 * from this forker thread. That will free some memory
+		 * and we can try again.
+		 */
+		if (!bdi->task) {
+			/*
+			 * Add this 'bdi' to the back, so we get
+			 * a chance to flush other bdi's to free
+			 * memory.
+			 */
+			mutex_lock(&bdi_lock);
+			list_add_tail(&bdi->bdi_list, &bdi_pending_list);
+			mutex_unlock(&bdi_lock);
+
+			bdi_flush_io(bdi);
+		}
+	}
+
+	return 0;
+}
+
+void bdi_add_default_flusher_task(struct backing_dev_info *bdi)
+{
+	if (test_and_set_bit(BDI_pending, &bdi->state))
+		return;
+
+	mutex_lock(&bdi_lock);
+	list_move_tail(&bdi->bdi_list, &bdi_pending_list);
+	mutex_unlock(&bdi_lock);
+
+	wake_up_process(default_backing_dev_info.task);
+}
+
 int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 		const char *fmt, ...)
 {
@@ -218,8 +405,25 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 	mutex_unlock(&bdi_lock);
 
 	bdi->dev = dev;
-	bdi_debug_register(bdi, dev_name(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)) {
+		bdi->task = kthread_run(bdi_forker_task, bdi, "bdi-%s",
+						dev_name(dev));
+		if (!bdi->task) {
+			mutex_lock(&bdi_lock);
+			list_del(&bdi->bdi_list);
+			mutex_unlock(&bdi_lock);
+			ret = -ENOMEM;
+			goto exit;
+		}
+	}
+
+	bdi_debug_register(bdi, dev_name(dev));
 exit:
 	return ret;
 }
@@ -231,8 +435,19 @@ int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
 }
 EXPORT_SYMBOL(bdi_register_dev);
 
-static void bdi_remove_from_list(struct backing_dev_info *bdi)
+static int sched_wait(void *word)
 {
+	schedule();
+	return 0;
+}
+
+static void bdi_wb_shutdown(struct backing_dev_info *bdi)
+{
+	/*
+	 * If setup is pending, wait for that to complete first
+	 */
+	wait_on_bit(&bdi->state, BDI_pending, sched_wait, TASK_UNINTERRUPTIBLE);
+
 	mutex_lock(&bdi_lock);
 	list_del(&bdi->bdi_list);
 	mutex_unlock(&bdi_lock);
@@ -241,7 +456,13 @@ static void bdi_remove_from_list(struct backing_dev_info *bdi)
 void bdi_unregister(struct backing_dev_info *bdi)
 {
 	if (bdi->dev) {
-		bdi_remove_from_list(bdi);
+		if (!bdi_cap_flush_forker(bdi)) {
+			bdi_wb_shutdown(bdi);
+			if (bdi->task) {
+				kthread_stop(bdi->task);
+				bdi->task = NULL;
+			}
+		}
 		bdi_debug_unregister(bdi);
 		device_unregister(bdi->dev);
 		bdi->dev = NULL;
@@ -251,8 +472,7 @@ EXPORT_SYMBOL(bdi_unregister);
 
 int bdi_init(struct backing_dev_info *bdi)
 {
-	int i;
-	int err;
+	int i, err;
 
 	bdi->dev = NULL;
 
@@ -277,8 +497,6 @@ int bdi_init(struct backing_dev_info *bdi)
 err:
 		while (i--)
 			percpu_counter_destroy(&bdi->bdi_stat[i]);
-
-		bdi_remove_from_list(bdi);
 	}
 
 	return err;
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 7c44314..91c8615 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -36,15 +36,6 @@
 #include <linux/pagevec.h>
 
 /*
- * The maximum number of pages to writeout in a single bdflush/kupdate
- * operation.  We do this so we don't hold I_SYNC 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.
  */
@@ -117,8 +108,6 @@ EXPORT_SYMBOL(laptop_mode);
 /* End of sysctl-exported parameters */
 
 
-static void background_writeout(unsigned long _min_pages);
-
 /*
  * Scale the writeback cache size proportional to the relative writeout speeds.
  *
@@ -539,7 +528,7 @@ static void balance_dirty_pages(struct address_space *mapping)
 		 * been flushed to permanent storage.
 		 */
 		if (bdi_nr_reclaimable) {
-			writeback_inodes(&wbc);
+			generic_sync_bdi_inodes(NULL, &wbc);
 			pages_written += write_chunk - wbc.nr_to_write;
 			get_dirty_limits(&background_thresh, &dirty_thresh,
 				       &bdi_thresh, bdi);
@@ -590,7 +579,7 @@ static void balance_dirty_pages(struct address_space *mapping)
 			(!laptop_mode && (global_page_state(NR_FILE_DIRTY)
 					  + global_page_state(NR_UNSTABLE_NFS)
 					  > background_thresh)))
-		pdflush_operation(background_writeout, 0);
+		bdi_start_writeback(bdi, NULL, 0, WB_SYNC_NONE);
 }
 
 void set_page_dirty_balance(struct page *page, int page_mkwrite)
@@ -675,152 +664,53 @@ void throttle_vm_writeout(gfp_t gfp_mask)
 }
 
 /*
- * 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.
+ * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
+ * the whole world.
  */
-static void background_writeout(unsigned long _min_pages)
+void wakeup_flusher_threads(long nr_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,
 		.range_cyclic	= 1,
 	};
 
-	for ( ; ; ) {
-		unsigned long background_thresh;
-		unsigned long dirty_thresh;
-
-		get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
-		if (global_page_state(NR_FILE_DIRTY) +
-			global_page_state(NR_UNSTABLE_NFS) < background_thresh
-				&& min_pages <= 0)
-			break;
-		wbc.more_io = 0;
-		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 */
-			if (wbc.encountered_congestion || wbc.more_io)
-				congestion_wait(WRITE, HZ/10);
-			else
-				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_pdflush(long nr_pages)
-{
 	if (nr_pages == 0)
 		nr_pages = global_page_state(NR_FILE_DIRTY) +
 				global_page_state(NR_UNSTABLE_NFS);
-	return pdflush_operation(background_writeout, nr_pages);
+	wbc.nr_to_write = nr_pages;
+	bdi_writeback_all(NULL, &wbc);
 }
 
-static void wb_timer_fn(unsigned long unused);
 static void laptop_timer_fn(unsigned long unused);
 
-static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0);
 static DEFINE_TIMER(laptop_mode_wb_timer, 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_interval.  But if a writeback event
- * takes longer than a dirty_writeback_interval 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_control wbc = {
-		.bdi		= NULL,
-		.sync_mode	= WB_SYNC_NONE,
-		.older_than_this = &oldest_jif,
-		.nr_to_write	= 0,
-		.nonblocking	= 1,
-		.for_kupdate	= 1,
-		.range_cyclic	= 1,
-	};
-
-	sync_supers();
-
-	oldest_jif = jiffies - msecs_to_jiffies(dirty_expire_interval * 10);
-	start_jif = jiffies;
-	next_jif = start_jif + msecs_to_jiffies(dirty_writeback_interval * 10);
-	nr_to_write = global_page_state(NR_FILE_DIRTY) +
-			global_page_state(NR_UNSTABLE_NFS) +
-			(inodes_stat.nr_inodes - inodes_stat.nr_unused);
-	while (nr_to_write > 0) {
-		wbc.more_io = 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 || wbc.more_io)
-				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_interval)
-		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_interval)
-		mod_timer(&wb_timer, jiffies +
-			msecs_to_jiffies(dirty_writeback_interval * 10));
-	else
-		del_timer(&wb_timer);
 	return 0;
 }
 
-static void wb_timer_fn(unsigned long unused)
+static void do_laptop_sync(struct work_struct *work)
 {
-	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();
+	wakeup_flusher_threads(0);
+	kfree(work);
 }
 
 static void laptop_timer_fn(unsigned long unused)
 {
-	pdflush_operation(laptop_flush, 0);
+	struct work_struct *work;
+
+	work = kmalloc(sizeof(*work), GFP_ATOMIC);
+	if (work) {
+		INIT_WORK(work, do_laptop_sync);
+		schedule_work(work);
+	}
 }
 
 /*
@@ -903,8 +793,6 @@ void __init page_writeback_init(void)
 {
 	int shift;
 
-	mod_timer(&wb_timer,
-		  jiffies + msecs_to_jiffies(dirty_writeback_interval * 10));
 	writeback_set_ratelimit();
 	register_cpu_notifier(&ratelimit_nb);
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index d254306..fddca74 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1656,7 +1656,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
 		 */
 		if (total_scanned > sc->swap_cluster_max +
 					sc->swap_cluster_max / 2) {
-			wakeup_pdflush(laptop_mode ? 0 : total_scanned);
+			wakeup_flusher_threads(laptop_mode ? 0 : total_scanned);
 			sc->may_writepage = 1;
 		}
 
-- 
1.6.3.rc0.1.gf800

[PATCH 06/15] writeback: get rid of pdflush completely

[Jens Axboe]

It is now unused, so kill it off.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 fs/fs-writeback.c         |    5 +
 include/linux/writeback.h |   12 --
 mm/Makefile               |    2 +-
 mm/pdflush.c              |  269 ---------------------------------------------
 4 files changed, 6 insertions(+), 282 deletions(-)
 delete mode 100644 mm/pdflush.c

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index f7a5e39..8b72388 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -29,6 +29,11 @@
 
 #define inode_to_bdi(inode)	((inode)->i_mapping->backing_dev_info)
 
+/*
+ * We don't actually have pdflush, but this one is exported though /proc...
+ */
+int nr_pdflush_threads;
+
 /**
  * writeback_acquire - attempt to get exclusive writeback access to a device
  * @bdi: the device's backing_dev_info structure
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 6999882..6e416a9 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -14,17 +14,6 @@ extern struct list_head inode_in_use;
 extern struct list_head inode_unused;
 
 /*
- * Yes, writeback.h requires sched.h
- * No, sched.h is not included from here.
- */
-static inline int task_is_pdflush(struct task_struct *task)
-{
-	return task->flags & PF_FLUSHER;
-}
-
-#define current_is_pdflush()	task_is_pdflush(current)
-
-/*
  * fs/fs-writeback.c
  */
 enum writeback_sync_modes {
@@ -150,7 +139,6 @@ balance_dirty_pages_ratelimited(struct address_space *mapping)
 typedef int (*writepage_t)(struct page *page, struct writeback_control *wbc,
 				void *data);
 
-int pdflush_operation(void (*fn)(unsigned long), unsigned long arg0);
 int generic_writepages(struct address_space *mapping,
 		       struct writeback_control *wbc);
 int write_cache_pages(struct address_space *mapping,
diff --git a/mm/Makefile b/mm/Makefile
index e89acb0..bddaea6 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -8,7 +8,7 @@ mmu-$(CONFIG_MMU)	:= fremap.o highmem.o madvise.o memory.o mincore.o \
 			   vmalloc.o
 
 obj-y			:= bootmem.o filemap.o mempool.o oom_kill.o fadvise.o \
-			   maccess.o page_alloc.o page-writeback.o pdflush.o \
+			   maccess.o page_alloc.o page-writeback.o \
 			   readahead.o swap.o truncate.o vmscan.o shmem.o \
 			   prio_tree.o util.o mmzone.o vmstat.o backing-dev.o \
 			   page_isolation.o mm_init.o $(mmu-y)
diff --git a/mm/pdflush.c b/mm/pdflush.c
deleted file mode 100644
index 235ac44..0000000
--- a/mm/pdflush.c
+++ /dev/null
@@ -1,269 +0,0 @@
-/*
- * mm/pdflush.c - worker threads for writing back filesystem data
- *
- * Copyright (C) 2002, Linus Torvalds.
- *
- * 09Apr2002	Andrew Morton
- *		Initial version
- * 29Feb2004	kaos@sgi.com
- *		Move worker thread creation to kthread to avoid chewing
- *		up stack space with nested calls to kernel_thread.
- */
-
-#include <linux/sched.h>
-#include <linux/list.h>
-#include <linux/signal.h>
-#include <linux/spinlock.h>
-#include <linux/gfp.h>
-#include <linux/init.h>
-#include <linux/module.h>
-#include <linux/fs.h>		/* Needed by writeback.h	  */
-#include <linux/writeback.h>	/* Prototypes pdflush_operation() */
-#include <linux/kthread.h>
-#include <linux/cpuset.h>
-#include <linux/freezer.h>
-
-
-/*
- * Minimum and maximum number of pdflush instances
- */
-#define MIN_PDFLUSH_THREADS	2
-#define MAX_PDFLUSH_THREADS	8
-
-static void start_one_pdflush_thread(void);
-
-
-/*
- * The pdflush threads are worker threads for writing back dirty data.
- * Ideally, we'd like one thread per active disk spindle.  But the disk
- * topology is very hard to divine at this level.   Instead, we take
- * care in various places to prevent more than one pdflush thread from
- * performing writeback against a single filesystem.  pdflush threads
- * have the PF_FLUSHER flag set in current->flags to aid in this.
- */
-
-/*
- * All the pdflush threads.  Protected by pdflush_lock
- */
-static LIST_HEAD(pdflush_list);
-static DEFINE_SPINLOCK(pdflush_lock);
-
-/*
- * The count of currently-running pdflush threads.  Protected
- * by pdflush_lock.
- *
- * Readable by sysctl, but not writable.  Published to userspace at
- * /proc/sys/vm/nr_pdflush_threads.
- */
-int nr_pdflush_threads = 0;
-
-/*
- * The time at which the pdflush thread pool last went empty
- */
-static unsigned long last_empty_jifs;
-
-/*
- * The pdflush thread.
- *
- * Thread pool management algorithm:
- * 
- * - The minimum and maximum number of pdflush instances are bound
- *   by MIN_PDFLUSH_THREADS and MAX_PDFLUSH_THREADS.
- * 
- * - If there have been no idle pdflush instances for 1 second, create
- *   a new one.
- * 
- * - If the least-recently-went-to-sleep pdflush thread has been asleep
- *   for more than one second, terminate a thread.
- */
-
-/*
- * A structure for passing work to a pdflush thread.  Also for passing
- * state information between pdflush threads.  Protected by pdflush_lock.
- */
-struct pdflush_work {
-	struct task_struct *who;	/* The thread */
-	void (*fn)(unsigned long);	/* A callback function */
-	unsigned long arg0;		/* An argument to the callback */
-	struct list_head list;		/* On pdflush_list, when idle */
-	unsigned long when_i_went_to_sleep;
-};
-
-static int __pdflush(struct pdflush_work *my_work)
-{
-	current->flags |= PF_FLUSHER | PF_SWAPWRITE;
-	set_freezable();
-	my_work->fn = NULL;
-	my_work->who = current;
-	INIT_LIST_HEAD(&my_work->list);
-
-	spin_lock_irq(&pdflush_lock);
-	for ( ; ; ) {
-		struct pdflush_work *pdf;
-
-		set_current_state(TASK_INTERRUPTIBLE);
-		list_move(&my_work->list, &pdflush_list);
-		my_work->when_i_went_to_sleep = jiffies;
-		spin_unlock_irq(&pdflush_lock);
-		schedule();
-		try_to_freeze();
-		spin_lock_irq(&pdflush_lock);
-		if (!list_empty(&my_work->list)) {
-			/*
-			 * Someone woke us up, but without removing our control
-			 * structure from the global list.  swsusp will do this
-			 * in try_to_freeze()->refrigerator().  Handle it.
-			 */
-			my_work->fn = NULL;
-			continue;
-		}
-		if (my_work->fn == NULL) {
-			printk("pdflush: bogus wakeup\n");
-			continue;
-		}
-		spin_unlock_irq(&pdflush_lock);
-
-		(*my_work->fn)(my_work->arg0);
-
-		spin_lock_irq(&pdflush_lock);
-
-		/*
-		 * Thread creation: For how long have there been zero
-		 * available threads?
-		 *
-		 * To throttle creation, we reset last_empty_jifs.
-		 */
-		if (time_after(jiffies, last_empty_jifs + 1 * HZ)) {
-			if (list_empty(&pdflush_list)) {
-				if (nr_pdflush_threads < MAX_PDFLUSH_THREADS) {
-					last_empty_jifs = jiffies;
-					nr_pdflush_threads++;
-					spin_unlock_irq(&pdflush_lock);
-					start_one_pdflush_thread();
-					spin_lock_irq(&pdflush_lock);
-				}
-			}
-		}
-
-		my_work->fn = NULL;
-
-		/*
-		 * Thread destruction: For how long has the sleepiest
-		 * thread slept?
-		 */
-		if (list_empty(&pdflush_list))
-			continue;
-		if (nr_pdflush_threads <= MIN_PDFLUSH_THREADS)
-			continue;
-		pdf = list_entry(pdflush_list.prev, struct pdflush_work, list);
-		if (time_after(jiffies, pdf->when_i_went_to_sleep + 1 * HZ)) {
-			/* Limit exit rate */
-			pdf->when_i_went_to_sleep = jiffies;
-			break;					/* exeunt */
-		}
-	}
-	nr_pdflush_threads--;
-	spin_unlock_irq(&pdflush_lock);
-	return 0;
-}
-
-/*
- * Of course, my_work wants to be just a local in __pdflush().  It is
- * separated out in this manner to hopefully prevent the compiler from
- * performing unfortunate optimisations against the auto variables.  Because
- * these are visible to other tasks and CPUs.  (No problem has actually
- * been observed.  This is just paranoia).
- */
-static int pdflush(void *dummy)
-{
-	struct pdflush_work my_work;
-	cpumask_var_t cpus_allowed;
-
-	/*
-	 * Since the caller doesn't even check kthread_run() worked, let's not
-	 * freak out too much if this fails.
-	 */
-	if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL)) {
-		printk(KERN_WARNING "pdflush failed to allocate cpumask\n");
-		return 0;
-	}
-
-	/*
-	 * pdflush can spend a lot of time doing encryption via dm-crypt.  We
-	 * don't want to do that at keventd's priority.
-	 */
-	set_user_nice(current, 0);
-
-	/*
-	 * Some configs put our parent kthread in a limited cpuset,
-	 * which kthread() overrides, forcing cpus_allowed == cpu_all_mask.
-	 * Our needs are more modest - cut back to our cpusets cpus_allowed.
-	 * This is needed as pdflush's are dynamically created and destroyed.
-	 * The boottime pdflush's are easily placed w/o these 2 lines.
-	 */
-	cpuset_cpus_allowed(current, cpus_allowed);
-	set_cpus_allowed_ptr(current, cpus_allowed);
-	free_cpumask_var(cpus_allowed);
-
-	return __pdflush(&my_work);
-}
-
-/*
- * Attempt to wake up a pdflush thread, and get it to do some work for you.
- * Returns zero if it indeed managed to find a worker thread, and passed your
- * payload to it.
- */
-int pdflush_operation(void (*fn)(unsigned long), unsigned long arg0)
-{
-	unsigned long flags;
-	int ret = 0;
-
-	BUG_ON(fn == NULL);	/* Hard to diagnose if it's deferred */
-
-	spin_lock_irqsave(&pdflush_lock, flags);
-	if (list_empty(&pdflush_list)) {
-		ret = -1;
-	} else {
-		struct pdflush_work *pdf;
-
-		pdf = list_entry(pdflush_list.next, struct pdflush_work, list);
-		list_del_init(&pdf->list);
-		if (list_empty(&pdflush_list))
-			last_empty_jifs = jiffies;
-		pdf->fn = fn;
-		pdf->arg0 = arg0;
-		wake_up_process(pdf->who);
-	}
-	spin_unlock_irqrestore(&pdflush_lock, flags);
-
-	return ret;
-}
-
-static void start_one_pdflush_thread(void)
-{
-	struct task_struct *k;
-
-	k = kthread_run(pdflush, NULL, "pdflush");
-	if (unlikely(IS_ERR(k))) {
-		spin_lock_irq(&pdflush_lock);
-		nr_pdflush_threads--;
-		spin_unlock_irq(&pdflush_lock);
-	}
-}
-
-static int __init pdflush_init(void)
-{
-	int i;
-
-	/*
-	 * Pre-set nr_pdflush_threads...  If we fail to create,
-	 * the count will be decremented.
-	 */
-	nr_pdflush_threads = MIN_PDFLUSH_THREADS;
-
-	for (i = 0; i < MIN_PDFLUSH_THREADS; i++)
-		start_one_pdflush_thread();
-	return 0;
-}
-
-module_init(pdflush_init);
-- 
1.6.3.rc0.1.gf800

[PATCH 07/15] writeback: separate the flushing state/task from the bdi

[Jens Axboe]

Add a struct bdi_writeback for tracking and handling dirty IO. This
is in preparation for adding > 1 flusher task per bdi.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 fs/fs-writeback.c           |  136 +++++++++++++++++++++++++++----------------
 include/linux/backing-dev.h |   38 +++++++-----
 mm/backing-dev.c            |  126 ++++++++++++++++++++++++++++++++--------
 3 files changed, 208 insertions(+), 92 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 8b72388..8a1a60c 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -46,9 +46,11 @@ int nr_pdflush_threads;
  * unless they implement their own.  Which is somewhat inefficient, as this
  * may prevent concurrent writeback against multiple devices.
  */
-static int writeback_acquire(struct backing_dev_info *bdi)
+static int writeback_acquire(struct bdi_writeback *wb)
 {
-	return !test_and_set_bit(BDI_pdflush, &bdi->state);
+	struct backing_dev_info *bdi = wb->bdi;
+
+	return !test_and_set_bit(wb->nr, &bdi->wb_active);
 }
 
 /**
@@ -59,19 +61,37 @@ static int writeback_acquire(struct backing_dev_info *bdi)
  */
 int writeback_in_progress(struct backing_dev_info *bdi)
 {
-	return test_bit(BDI_pdflush, &bdi->state);
+	return bdi->wb_active != 0;
 }
 
 /**
  * writeback_release - relinquish exclusive writeback access against a device.
  * @bdi: the device's backing_dev_info structure
  */
-static void writeback_release(struct backing_dev_info *bdi)
+static void writeback_release(struct bdi_writeback *wb)
 {
-	WARN_ON_ONCE(!writeback_in_progress(bdi));
-	bdi->wb_arg.nr_pages = 0;
-	bdi->wb_arg.sb = NULL;
-	clear_bit(BDI_pdflush, &bdi->state);
+	struct backing_dev_info *bdi = wb->bdi;
+
+	wb->nr_pages = 0;
+	wb->sb = NULL;
+	clear_bit(wb->nr, &bdi->wb_active);
+}
+
+static void wb_start_writeback(struct bdi_writeback *wb, struct super_block *sb,
+			       long nr_pages,
+			       enum writeback_sync_modes sync_mode)
+{
+	if (!wb_has_dirty_io(wb))
+		return;
+
+	if (writeback_acquire(wb)) {
+		wb->nr_pages = nr_pages;
+		wb->sb = sb;
+		wb->sync_mode = sync_mode;
+
+		if (wb->task)
+			wake_up_process(wb->task);
+	}
 }
 
 int bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
@@ -81,20 +101,12 @@ int bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
 	 * This only happens the first time someone kicks this bdi, so put
 	 * it out-of-line.
 	 */
-	if (unlikely(!bdi->task)) {
+	if (unlikely(!bdi->wb.task)) {
 		bdi_add_default_flusher_task(bdi);
 		return 1;
 	}
 
-	if (writeback_acquire(bdi)) {
-		bdi->wb_arg.nr_pages = nr_pages;
-		bdi->wb_arg.sb = sb;
-		bdi->wb_arg.sync_mode = sync_mode;
-
-		if (bdi->task)
-			wake_up_process(bdi->task);
-	}
-
+	wb_start_writeback(&bdi->wb, sb, nr_pages, sync_mode);
 	return 0;
 }
 
@@ -122,12 +134,12 @@ int bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
  * 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 bdi_kupdated(struct backing_dev_info *bdi)
+static void wb_kupdated(struct bdi_writeback *wb)
 {
 	unsigned long oldest_jif;
 	long nr_to_write;
 	struct writeback_control wbc = {
-		.bdi			= bdi,
+		.bdi			= wb->bdi,
 		.sync_mode		= WB_SYNC_NONE,
 		.older_than_this	= &oldest_jif,
 		.nr_to_write		= 0,
@@ -162,15 +174,19 @@ static inline bool over_bground_thresh(void)
 		global_page_state(NR_UNSTABLE_NFS) >= background_thresh);
 }
 
-static void bdi_pdflush(struct backing_dev_info *bdi)
+static void generic_sync_wb_inodes(struct bdi_writeback *wb,
+				   struct super_block *sb,
+				   struct writeback_control *wbc);
+
+static void wb_writeback(struct bdi_writeback *wb)
 {
 	struct writeback_control wbc = {
-		.bdi			= bdi,
-		.sync_mode		= bdi->wb_arg.sync_mode,
+		.bdi			= wb->bdi,
+		.sync_mode		= wb->sync_mode,
 		.older_than_this	= NULL,
 		.range_cyclic		= 1,
 	};
-	long nr_pages = bdi->wb_arg.nr_pages;
+	long nr_pages = wb->nr_pages;
 
 	for (;;) {
 		if (wbc.sync_mode == WB_SYNC_NONE && nr_pages <= 0 &&
@@ -181,7 +197,7 @@ static void bdi_pdflush(struct backing_dev_info *bdi)
 		wbc.encountered_congestion = 0;
 		wbc.nr_to_write = MAX_WRITEBACK_PAGES;
 		wbc.pages_skipped = 0;
-		generic_sync_bdi_inodes(bdi->wb_arg.sb, &wbc);
+		generic_sync_wb_inodes(wb, wb->sb, &wbc);
 		nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
 		/*
 		 * If we ran out of stuff to write, bail unless more_io got set
@@ -198,7 +214,7 @@ static void bdi_pdflush(struct backing_dev_info *bdi)
  * Handle writeback of dirty data for the device backed by this bdi. Also
  * wakes up periodically and does kupdated style flushing.
  */
-int bdi_writeback_task(struct backing_dev_info *bdi)
+int bdi_writeback_task(struct bdi_writeback *wb)
 {
 	while (!kthread_should_stop()) {
 		unsigned long wait_jiffies;
@@ -222,12 +238,12 @@ int bdi_writeback_task(struct backing_dev_info *bdi)
 		 *  pdflush style writeout.
 		 *
 		 */
-		if (writeback_acquire(bdi))
-			bdi_kupdated(bdi);
+		if (writeback_acquire(wb))
+			wb_kupdated(wb);
 		else
-			bdi_pdflush(bdi);
+			wb_writeback(wb);
 
-		writeback_release(bdi);
+		writeback_release(wb);
 	}
 
 	return 0;
@@ -270,6 +286,14 @@ static noinline void block_dump___mark_inode_dirty(struct inode *inode)
 	}
 }
 
+/*
+ * We have only a single wb per bdi, so just return that.
+ */
+static inline struct bdi_writeback *inode_get_wb(struct inode *inode)
+{
+	return &inode_to_bdi(inode)->wb;
+}
+
 /**
  *	__mark_inode_dirty -	internal function
  *	@inode: inode to mark
@@ -353,9 +377,10 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 		 * reposition it (that would break b_dirty time-ordering).
 		 */
 		if (!was_dirty) {
+			struct bdi_writeback *wb = inode_get_wb(inode);
+
 			inode->dirtied_when = jiffies;
-			list_move(&inode->i_list,
-					&inode_to_bdi(inode)->b_dirty);
+			list_move(&inode->i_list, &wb->b_dirty);
 		}
 	}
 out:
@@ -382,16 +407,16 @@ static int write_inode(struct inode *inode, int sync)
  */
 static void redirty_tail(struct inode *inode)
 {
-	struct backing_dev_info *bdi = inode_to_bdi(inode);
+	struct bdi_writeback *wb = inode_get_wb(inode);
 
-	if (!list_empty(&bdi->b_dirty)) {
+	if (!list_empty(&wb->b_dirty)) {
 		struct inode *tail;
 
-		tail = list_entry(bdi->b_dirty.next, struct inode, i_list);
+		tail = list_entry(wb->b_dirty.next, struct inode, i_list);
 		if (time_before(inode->dirtied_when, tail->dirtied_when))
 			inode->dirtied_when = jiffies;
 	}
-	list_move(&inode->i_list, &bdi->b_dirty);
+	list_move(&inode->i_list, &wb->b_dirty);
 }
 
 /*
@@ -399,7 +424,9 @@ static void redirty_tail(struct inode *inode)
  */
 static void requeue_io(struct inode *inode)
 {
-	list_move(&inode->i_list, &inode_to_bdi(inode)->b_more_io);
+	struct bdi_writeback *wb = inode_get_wb(inode);
+
+	list_move(&inode->i_list, &wb->b_more_io);
 }
 
 static void inode_sync_complete(struct inode *inode)
@@ -446,11 +473,10 @@ static void move_expired_inodes(struct list_head *delaying_queue,
 /*
  * Queue all expired dirty inodes for io, eldest first.
  */
-static void queue_io(struct backing_dev_info *bdi,
-		     unsigned long *older_than_this)
+static void queue_io(struct bdi_writeback *wb, unsigned long *older_than_this)
 {
-	list_splice_init(&bdi->b_more_io, bdi->b_io.prev);
-	move_expired_inodes(&bdi->b_dirty, &bdi->b_io, older_than_this);
+	list_splice_init(&wb->b_more_io, wb->b_io.prev);
+	move_expired_inodes(&wb->b_dirty, &wb->b_io, older_than_this);
 }
 
 /*
@@ -609,20 +635,20 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
 	return __sync_single_inode(inode, wbc);
 }
 
-void generic_sync_bdi_inodes(struct super_block *sb,
-			     struct writeback_control *wbc)
+static void generic_sync_wb_inodes(struct bdi_writeback *wb,
+				   struct super_block *sb,
+				   struct writeback_control *wbc)
 {
 	const int is_blkdev_sb = sb_is_blkdev_sb(sb);
-	struct backing_dev_info *bdi = wbc->bdi;
 	const unsigned long start = jiffies;	/* livelock avoidance */
 
 	spin_lock(&inode_lock);
 
-	if (!wbc->for_kupdate || list_empty(&bdi->b_io))
-		queue_io(bdi, wbc->older_than_this);
+	if (!wbc->for_kupdate || list_empty(&wb->b_io))
+		queue_io(wb, wbc->older_than_this);
 
-	while (!list_empty(&bdi->b_io)) {
-		struct inode *inode = list_entry(bdi->b_io.prev,
+	while (!list_empty(&wb->b_io)) {
+		struct inode *inode = list_entry(wb->b_io.prev,
 						struct inode, i_list);
 		long pages_skipped;
 
@@ -634,7 +660,7 @@ void generic_sync_bdi_inodes(struct super_block *sb,
 			continue;
 		}
 
-		if (!bdi_cap_writeback_dirty(bdi)) {
+		if (!bdi_cap_writeback_dirty(wb->bdi)) {
 			redirty_tail(inode);
 			if (is_blkdev_sb) {
 				/*
@@ -656,7 +682,7 @@ void generic_sync_bdi_inodes(struct super_block *sb,
 			continue;
 		}
 
-		if (wbc->nonblocking && bdi_write_congested(bdi)) {
+		if (wbc->nonblocking && bdi_write_congested(wb->bdi)) {
 			wbc->encountered_congestion = 1;
 			if (!is_blkdev_sb)
 				break;		/* Skip a congested fs */
@@ -690,7 +716,7 @@ void generic_sync_bdi_inodes(struct super_block *sb,
 			wbc->more_io = 1;
 			break;
 		}
-		if (!list_empty(&bdi->b_more_io))
+		if (!list_empty(&wb->b_more_io))
 			wbc->more_io = 1;
 	}
 
@@ -698,6 +724,14 @@ void generic_sync_bdi_inodes(struct super_block *sb,
 	/* Leave any unwritten inodes on b_io */
 }
 
+void generic_sync_bdi_inodes(struct super_block *sb,
+			     struct writeback_control *wbc)
+{
+	struct backing_dev_info *bdi = wbc->bdi;
+
+	generic_sync_wb_inodes(&bdi->wb, sb, wbc);
+}
+
 /*
  * Write out a superblock's list of dirty inodes.  A wait will be performed
  * upon no inodes, all inodes or the final one, depending upon sync_mode.
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 12e387b..1845625 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -24,8 +24,8 @@ struct dentry;
  * Bits in backing_dev_info.state
  */
 enum bdi_state {
-	BDI_pdflush,		/* A pdflush thread is working this device */
 	BDI_pending,		/* On its way to being activated */
+	BDI_wb_alloc,		/* Default embedded wb allocated */
 	BDI_async_congested,	/* The async (write) queue is getting full */
 	BDI_sync_congested,	/* The sync queue is getting full */
 	BDI_unused,		/* Available bits start here */
@@ -41,15 +41,22 @@ enum bdi_stat_item {
 
 #define BDI_STAT_BATCH (8*(1+ilog2(nr_cpu_ids)))
 
-struct bdi_writeback_arg {
-	unsigned long nr_pages;
-	struct super_block *sb;
+struct bdi_writeback {
+	struct backing_dev_info *bdi;		/* our parent bdi */
+	unsigned int nr;
+
+	struct task_struct	*task;		/* writeback task */
+	struct list_head	b_dirty;	/* dirty inodes */
+	struct list_head	b_io;		/* parked for writeback */
+	struct list_head	b_more_io;	/* parked for more writeback */
+
+	unsigned long		nr_pages;
+	struct super_block	*sb;
 	enum writeback_sync_modes sync_mode;
 };
 
 struct backing_dev_info {
 	struct list_head bdi_list;
-
 	unsigned long ra_pages;	/* max readahead in PAGE_CACHE_SIZE units */
 	unsigned long state;	/* Always use atomic bitops on this */
 	unsigned int capabilities; /* Device capabilities */
@@ -66,13 +73,11 @@ struct backing_dev_info {
 	unsigned int min_ratio;
 	unsigned int max_ratio, max_prop_frac;
 
-	struct device *dev;
+	struct bdi_writeback wb;  /* default writeback info for this bdi */
+	unsigned long wb_active;  /* bitmap of active tasks */
+	unsigned long wb_mask;	  /* number of registered tasks */
 
-	struct task_struct	*task;		/* writeback task */
-	struct bdi_writeback_arg wb_arg;	/* protected by BDI_pdflush */
-	struct list_head	b_dirty;	/* dirty inodes */
-	struct list_head	b_io;		/* parked for writeback */
-	struct list_head	b_more_io;	/* parked for more writeback */
+	struct device *dev;
 
 #ifdef CONFIG_DEBUG_FS
 	struct dentry *debug_dir;
@@ -89,18 +94,19 @@ int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev);
 void bdi_unregister(struct backing_dev_info *bdi);
 int bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
 			 long nr_pages, enum writeback_sync_modes sync_mode);
-int bdi_writeback_task(struct backing_dev_info *bdi);
+int bdi_writeback_task(struct bdi_writeback *wb);
 void bdi_writeback_all(struct super_block *sb, struct writeback_control *wbc);
 void bdi_add_default_flusher_task(struct backing_dev_info *bdi);
+int bdi_has_dirty_io(struct backing_dev_info *bdi);
 
 extern struct mutex bdi_lock;
 extern struct list_head bdi_list;
 
-static inline int bdi_has_dirty_io(struct backing_dev_info *bdi)
+static inline int wb_has_dirty_io(struct bdi_writeback *wb)
 {
-	return !list_empty(&bdi->b_dirty) ||
-	       !list_empty(&bdi->b_io) ||
-	       !list_empty(&bdi->b_more_io);
+	return !list_empty(&wb->b_dirty) ||
+	       !list_empty(&wb->b_io) ||
+	       !list_empty(&wb->b_more_io);
 }
 
 static inline void __add_bdi_stat(struct backing_dev_info *bdi,
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index c620c93..e6c316a 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -213,10 +213,45 @@ static int __init default_bdi_init(void)
 }
 subsys_initcall(default_bdi_init);
 
+static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
+{
+	memset(wb, 0, sizeof(*wb));
+
+	wb->bdi = bdi;
+	INIT_LIST_HEAD(&wb->b_dirty);
+	INIT_LIST_HEAD(&wb->b_io);
+	INIT_LIST_HEAD(&wb->b_more_io);
+}
+
+static int wb_assign_nr(struct backing_dev_info *bdi, struct bdi_writeback *wb)
+{
+	set_bit(0, &bdi->wb_mask);
+	wb->nr = 0;
+	return 0;
+}
+
+static void bdi_put_wb(struct backing_dev_info *bdi, struct bdi_writeback *wb)
+{
+	clear_bit(wb->nr, &bdi->wb_mask);
+	clear_bit(BDI_wb_alloc, &bdi->state);
+}
+
+static struct bdi_writeback *bdi_new_wb(struct backing_dev_info *bdi)
+{
+	struct bdi_writeback *wb;
+
+	set_bit(BDI_wb_alloc, &bdi->state);
+	wb = &bdi->wb;
+	wb_assign_nr(bdi, wb);
+	return wb;
+}
+
 static int bdi_start_fn(void *ptr)
 {
-	struct backing_dev_info *bdi = ptr;
+	struct bdi_writeback *wb = ptr;
+	struct backing_dev_info *bdi = wb->bdi;
 	struct task_struct *tsk = current;
+	int ret;
 
 	/*
 	 * Add us to the active bdi_list
@@ -240,7 +275,15 @@ static int bdi_start_fn(void *ptr)
 	smp_mb__after_clear_bit();
 	wake_up_bit(&bdi->state, BDI_pending);
 
-	return bdi_writeback_task(bdi);
+	ret = bdi_writeback_task(wb);
+
+	bdi_put_wb(bdi, wb);
+	return ret;
+}
+
+int bdi_has_dirty_io(struct backing_dev_info *bdi)
+{
+	return wb_has_dirty_io(&bdi->wb);
 }
 
 static void bdi_flush_io(struct backing_dev_info *bdi)
@@ -295,17 +338,18 @@ static void sync_supers_timer_fn(unsigned long unused)
 
 static int bdi_forker_task(void *ptr)
 {
-	struct backing_dev_info *me = ptr;
+	struct bdi_writeback *me = ptr;
 
 	for (;;) {
 		struct backing_dev_info *bdi, *tmp;
+		struct bdi_writeback *wb;
 
 		/*
 		 * Temporary measure, we want to make sure we don't see
 		 * dirty data on the default backing_dev_info
 		 */
-		if (bdi_has_dirty_io(me))
-			bdi_flush_io(me);
+		if (wb_has_dirty_io(me))
+			bdi_flush_io(me->bdi);
 
 		mutex_lock(&bdi_lock);
 
@@ -314,7 +358,7 @@ static int bdi_forker_task(void *ptr)
 		 * a thread registered. If so, set that up.
 		 */
 		list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
-			if (bdi->task || !bdi_has_dirty_io(bdi))
+			if (bdi->wb.task || !bdi_has_dirty_io(bdi))
 				continue;
 
 			bdi_add_default_flusher_task(bdi);
@@ -343,17 +387,22 @@ static int bdi_forker_task(void *ptr)
 		list_del_init(&bdi->bdi_list);
 		mutex_unlock(&bdi_lock);
 
-		BUG_ON(bdi->task);
+		wb = bdi_new_wb(bdi);
+		if (!wb)
+			goto readd_flush;
 
-		bdi->task = kthread_run(bdi_start_fn, bdi, "flush-%s",
+		wb->task = kthread_run(bdi_start_fn, wb, "flush-%s",
 					dev_name(bdi->dev));
+
 		/*
 		 * If task creation fails, then readd the bdi to
 		 * the pending list and force writeout of the bdi
 		 * from this forker thread. That will free some memory
 		 * and we can try again.
 		 */
-		if (!bdi->task) {
+		if (!wb->task) {
+			bdi_put_wb(bdi, wb);
+readd_flush:
 			/*
 			 * Add this 'bdi' to the back, so we get
 			 * a chance to flush other bdi's to free
@@ -370,8 +419,18 @@ static int bdi_forker_task(void *ptr)
 	return 0;
 }
 
+/*
+ * Add a new flusher task that gets created for any bdi
+ * that has dirty data pending writeout
+ */
 void bdi_add_default_flusher_task(struct backing_dev_info *bdi)
 {
+	if (!bdi_cap_writeback_dirty(bdi))
+		return;
+
+	/*
+	 * Someone already marked this pending for task creation
+	 */
 	if (test_and_set_bit(BDI_pending, &bdi->state))
 		return;
 
@@ -379,7 +438,7 @@ void bdi_add_default_flusher_task(struct backing_dev_info *bdi)
 	list_move_tail(&bdi->bdi_list, &bdi_pending_list);
 	mutex_unlock(&bdi_lock);
 
-	wake_up_process(default_backing_dev_info.task);
+	wake_up_process(default_backing_dev_info.wb.task);
 }
 
 int bdi_register(struct backing_dev_info *bdi, struct device *parent,
@@ -412,13 +471,23 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 	 * on-demand when they need it.
 	 */
 	if (bdi_cap_flush_forker(bdi)) {
-		bdi->task = kthread_run(bdi_forker_task, bdi, "bdi-%s",
+		struct bdi_writeback *wb;
+
+		wb = bdi_new_wb(bdi);
+		if (!wb) {
+			ret = -ENOMEM;
+			goto remove_err;
+		}
+
+		wb->task = kthread_run(bdi_forker_task, wb, "bdi-%s",
 						dev_name(dev));
-		if (!bdi->task) {
+		if (!wb->task) {
+			bdi_put_wb(bdi, wb);
+			ret = -ENOMEM;
+remove_err:
 			mutex_lock(&bdi_lock);
 			list_del(&bdi->bdi_list);
 			mutex_unlock(&bdi_lock);
-			ret = -ENOMEM;
 			goto exit;
 		}
 	}
@@ -441,28 +510,37 @@ static int sched_wait(void *word)
 	return 0;
 }
 
+/*
+ * Remove bdi from 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;
+
 	/*
 	 * If setup is pending, wait for that to complete first
 	 */
 	wait_on_bit(&bdi->state, BDI_pending, sched_wait, TASK_UNINTERRUPTIBLE);
 
+	/*
+	 * Make sure nobody finds us on the bdi_list anymore
+	 */
 	mutex_lock(&bdi_lock);
 	list_del(&bdi->bdi_list);
 	mutex_unlock(&bdi_lock);
+
+	/*
+	 * Finally, kill the kernel thread
+	 */
+	kthread_stop(bdi->wb.task);
 }
 
 void bdi_unregister(struct backing_dev_info *bdi)
 {
 	if (bdi->dev) {
-		if (!bdi_cap_flush_forker(bdi)) {
+		if (!bdi_cap_flush_forker(bdi))
 			bdi_wb_shutdown(bdi);
-			if (bdi->task) {
-				kthread_stop(bdi->task);
-				bdi->task = NULL;
-			}
-		}
 		bdi_debug_unregister(bdi);
 		device_unregister(bdi->dev);
 		bdi->dev = NULL;
@@ -480,9 +558,9 @@ int bdi_init(struct backing_dev_info *bdi)
 	bdi->max_ratio = 100;
 	bdi->max_prop_frac = PROP_FRAC_BASE;
 	INIT_LIST_HEAD(&bdi->bdi_list);
-	INIT_LIST_HEAD(&bdi->b_io);
-	INIT_LIST_HEAD(&bdi->b_dirty);
-	INIT_LIST_HEAD(&bdi->b_more_io);
+	bdi->wb_mask = bdi->wb_active = 0;
+
+	bdi_wb_init(&bdi->wb, bdi);
 
 	for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
 		err = percpu_counter_init(&bdi->bdi_stat[i], 0);
@@ -507,9 +585,7 @@ void bdi_destroy(struct backing_dev_info *bdi)
 {
 	int i;
 
-	WARN_ON(!list_empty(&bdi->b_dirty));
-	WARN_ON(!list_empty(&bdi->b_io));
-	WARN_ON(!list_empty(&bdi->b_more_io));
+	WARN_ON(bdi_has_dirty_io(bdi));
 
 	bdi_unregister(bdi);
 
-- 
1.6.3.rc0.1.gf800

[PATCH 08/15] writeback: support > 1 flusher thread per bdi

[Jens Axboe]

Build on the bdi_writeback support by allowing registration of
more than 1 flusher thread. File systems can call bdi_add_flusher_task(bdi)
to add more flusher threads to the device. If they do so, they must also
provide a super_operations function to return the suitable bdi_writeback
struct from any given inode.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 fs/fs-writeback.c           |  445 +++++++++++++++++++++++++++++++++++--------
 include/linux/backing-dev.h |   34 +++-
 include/linux/fs.h          |    3 +
 include/linux/writeback.h   |    1 +
 mm/backing-dev.c            |  242 +++++++++++++++++++-----
 5 files changed, 592 insertions(+), 133 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 8a1a60c..a652693 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -34,80 +34,249 @@
  */
 int nr_pdflush_threads;
 
-/**
- * writeback_acquire - attempt to get exclusive writeback access to a device
- * @bdi: the device's backing_dev_info structure
- *
- * It is a waste of resources to have more than one pdflush thread blocked on
- * a single request queue.  Exclusion at the request_queue level is obtained
- * via a flag in the request_queue's backing_dev_info.state.
- *
- * Non-request_queue-backed address_spaces will share default_backing_dev_info,
- * unless they implement their own.  Which is somewhat inefficient, as this
- * may prevent concurrent writeback against multiple devices.
+static void generic_sync_wb_inodes(struct bdi_writeback *wb,
+				   struct super_block *sb,
+				   struct writeback_control *wbc);
+
+/*
+ * Work items for the bdi_writeback threads
  */
-static int writeback_acquire(struct bdi_writeback *wb)
+struct bdi_work {
+	struct list_head list;
+	struct list_head wait_list;
+	struct rcu_head rcu_head;
+
+	unsigned long seen;
+	atomic_t pending;
+
+	unsigned long sb_data;
+	unsigned long nr_pages;
+	enum writeback_sync_modes sync_mode;
+
+	unsigned long state;
+};
+
+static struct super_block *bdi_work_sb(struct bdi_work *work)
 {
-	struct backing_dev_info *bdi = wb->bdi;
+	return (struct super_block *) (work->sb_data & ~1UL);
+}
+
+static inline bool bdi_work_on_stack(struct bdi_work *work)
+{
+	return work->sb_data & 1UL;
+}
 
-	return !test_and_set_bit(wb->nr, &bdi->wb_active);
+static inline void bdi_work_init(struct bdi_work *work, struct super_block *sb,
+				 unsigned long nr_pages,
+				 enum writeback_sync_modes sync_mode)
+{
+	INIT_RCU_HEAD(&work->rcu_head);
+	work->sb_data = (unsigned long) sb;
+	work->nr_pages = nr_pages;
+	work->sync_mode = sync_mode;
+	work->state = 1;
+}
+
+static inline void bdi_work_init_on_stack(struct bdi_work *work,
+					  struct super_block *sb,
+					  unsigned long nr_pages,
+					  enum writeback_sync_modes sync_mode)
+{
+	bdi_work_init(work, sb, nr_pages, sync_mode);
+	work->sb_data |= 1UL;
 }
 
 /**
  * writeback_in_progress - determine whether there is writeback in progress
  * @bdi: the device's backing_dev_info structure.
  *
- * Determine whether there is writeback in progress against a backing device.
+ * Determine whether there is writeback waiting to be handled against a
+ * backing device.
  */
 int writeback_in_progress(struct backing_dev_info *bdi)
 {
-	return bdi->wb_active != 0;
+	return !list_empty(&bdi->work_list);
 }
 
-/**
- * writeback_release - relinquish exclusive writeback access against a device.
- * @bdi: the device's backing_dev_info structure
- */
-static void writeback_release(struct bdi_writeback *wb)
+static void bdi_work_clear(struct bdi_work *work)
 {
-	struct backing_dev_info *bdi = wb->bdi;
+	clear_bit(0, &work->state);
+	smp_mb__after_clear_bit();
+	wake_up_bit(&work->state, 0);
+}
 
-	wb->nr_pages = 0;
-	wb->sb = NULL;
-	clear_bit(wb->nr, &bdi->wb_active);
+static void bdi_work_free(struct rcu_head *head)
+{
+	struct bdi_work *work = container_of(head, struct bdi_work, rcu_head);
+
+	if (!bdi_work_on_stack(work))
+		kfree(work);
+	else
+		bdi_work_clear(work);
 }
 
-static void wb_start_writeback(struct bdi_writeback *wb, struct super_block *sb,
-			       long nr_pages,
-			       enum writeback_sync_modes sync_mode)
+static void wb_work_complete(struct bdi_work *work)
 {
-	if (!wb_has_dirty_io(wb))
-		return;
+	const enum writeback_sync_modes sync_mode = work->sync_mode;
 
-	if (writeback_acquire(wb)) {
-		wb->nr_pages = nr_pages;
-		wb->sb = sb;
-		wb->sync_mode = sync_mode;
+	/*
+	 * For allocated work, we can clear the done/seen bit right here.
+	 * For on-stack work, we need to postpone both the clear and free
+	 * to after the RCU grace period, since the stack could be invalidated
+	 * as soon as bdi_work_clear() has done the wakeup.
+	 */
+	if (!bdi_work_on_stack(work))
+		bdi_work_clear(work);
+	if (sync_mode == WB_SYNC_NONE || bdi_work_on_stack(work))
+		call_rcu(&work->rcu_head, bdi_work_free);
+}
 
-		if (wb->task)
-			wake_up_process(wb->task);
+static void wb_clear_pending(struct bdi_writeback *wb, struct bdi_work *work)
+{
+	/*
+	 * The caller has retrieved the work arguments from this work,
+	 * drop our reference. If this is the last ref, delete and free it
+	 */
+	if (atomic_dec_and_test(&work->pending)) {
+		struct backing_dev_info *bdi = wb->bdi;
+
+		spin_lock(&bdi->wb_lock);
+		list_del_rcu(&work->list);
+		spin_unlock(&bdi->wb_lock);
+
+		wb_work_complete(work);
 	}
 }
 
-int bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
-			 long nr_pages, enum writeback_sync_modes sync_mode)
+static void wb_start_writeback(struct bdi_writeback *wb, struct bdi_work *work)
 {
 	/*
-	 * This only happens the first time someone kicks this bdi, so put
-	 * it out-of-line.
+	 * If we failed allocating the bdi work item, wake up the wb thread
+	 * always. As a safety precaution, it'll flush out everything
 	 */
-	if (unlikely(!bdi->wb.task)) {
+	if (!wb_has_dirty_io(wb) && work)
+		wb_clear_pending(wb, work);
+	else if (wb->task)
+		wake_up_process(wb->task);
+}
+
+static void bdi_queue_work(struct backing_dev_info *bdi, struct bdi_work *work)
+{
+	if (work) {
+		work->seen = bdi->wb_mask;
+		BUG_ON(!work->seen);
+		atomic_set(&work->pending, bdi->wb_cnt);
+		BUG_ON(!bdi->wb_cnt);
+
+		/*
+		 * Make sure stores are seen before it appears on the list
+		 */
+		smp_mb();
+
+		spin_lock(&bdi->wb_lock);
+		list_add_tail_rcu(&work->list, &bdi->work_list);
+		spin_unlock(&bdi->wb_lock);
+	}
+}
+
+static void bdi_sched_work(struct backing_dev_info *bdi, struct bdi_work *work)
+{
+	if (!bdi_wblist_needs_lock(bdi))
+		wb_start_writeback(&bdi->wb, work);
+	else {
+		struct bdi_writeback *wb;
+		int idx;
+
+		idx = srcu_read_lock(&bdi->srcu);
+
+		list_for_each_entry_rcu(wb, &bdi->wb_list, list)
+			wb_start_writeback(wb, work);
+
+		srcu_read_unlock(&bdi->srcu, idx);
+	}
+}
+
+static void __bdi_start_work(struct backing_dev_info *bdi,
+			     struct bdi_work *work)
+{
+	/*
+	 * If the default thread isn't there, make sure we add it. When
+	 * it gets created and wakes up, we'll run this work.
+	 */
+	if (unlikely(list_empty_careful(&bdi->wb_list)))
 		bdi_add_default_flusher_task(bdi);
-		return 1;
+	else
+		bdi_sched_work(bdi, work);
+}
+
+static void bdi_start_work(struct backing_dev_info *bdi, struct bdi_work *work)
+{
+	/*
+	 * If the default thread isn't there, make sure we add it. When
+	 * it gets created and wakes up, we'll run this work.
+	 */
+	if (unlikely(list_empty_careful(&bdi->wb_list))) {
+		mutex_lock(&bdi_lock);
+		bdi_add_default_flusher_task(bdi);
+		mutex_unlock(&bdi_lock);
+	} else
+		bdi_sched_work(bdi, work);
+}
+
+/*
+ * Used for on-stack allocated work items. The caller needs to wait until
+ * the wb threads have acked the work before it's safe to continue.
+ */
+static void bdi_wait_on_work_clear(struct bdi_work *work)
+{
+	wait_on_bit(&work->state, 0, bdi_sched_wait, TASK_UNINTERRUPTIBLE);
+}
+
+static struct bdi_work *bdi_alloc_work(struct super_block *sb, long nr_pages,
+				       enum writeback_sync_modes sync_mode)
+{
+	struct bdi_work *work;
+
+	work = kmalloc(sizeof(*work), GFP_ATOMIC);
+	if (work)
+		bdi_work_init(work, sb, nr_pages, sync_mode);
+
+	return work;
+}
+
+void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
+			 long nr_pages, enum writeback_sync_modes sync_mode)
+{
+	const bool must_wait = sync_mode == WB_SYNC_ALL;
+	struct bdi_work work_stack, *work = NULL;
+
+	if (!must_wait)
+		work = bdi_alloc_work(sb, nr_pages, sync_mode);
+
+	if (!work) {
+		work = &work_stack;
+		bdi_work_init_on_stack(work, sb, nr_pages, sync_mode);
 	}
 
-	wb_start_writeback(&bdi->wb, sb, nr_pages, sync_mode);
-	return 0;
+	bdi_queue_work(bdi, work);
+	bdi_start_work(bdi, work);
+
+	/*
+	 * If the sync mode is WB_SYNC_ALL, block waiting for the work to
+	 * complete. If not, we only need to wait for the work to be started,
+	 * if we allocated it on-stack. We use the same mechanism, if the
+	 * wait bit is set in the bdi_work struct, then threads will not
+	 * clear pending until after they are done.
+	 *
+	 * Note that work == &work_stack if must_wait is true, so we don't
+	 * need to do call_rcu() here ever, since the completion path will
+	 * have done that for us.
+	 */
+	if (must_wait || work == &work_stack) {
+		bdi_wait_on_work_clear(work);
+		if (work != &work_stack)
+			call_rcu(&work->rcu_head, bdi_work_free);
+	}
 }
 
 /*
@@ -157,7 +326,7 @@ static void wb_kupdated(struct bdi_writeback *wb)
 		wbc.more_io = 0;
 		wbc.encountered_congestion = 0;
 		wbc.nr_to_write = MAX_WRITEBACK_PAGES;
-		generic_sync_bdi_inodes(NULL, &wbc);
+		generic_sync_wb_inodes(wb, NULL, &wbc);
 		if (wbc.nr_to_write > 0)
 			break;	/* All the old data is written */
 		nr_to_write -= MAX_WRITEBACK_PAGES;
@@ -174,22 +343,19 @@ static inline bool over_bground_thresh(void)
 		global_page_state(NR_UNSTABLE_NFS) >= background_thresh);
 }
 
-static void generic_sync_wb_inodes(struct bdi_writeback *wb,
-				   struct super_block *sb,
-				   struct writeback_control *wbc);
-
-static void wb_writeback(struct bdi_writeback *wb)
+static void __wb_writeback(struct bdi_writeback *wb, long nr_pages,
+			   struct super_block *sb,
+			   enum writeback_sync_modes sync_mode)
 {
 	struct writeback_control wbc = {
 		.bdi			= wb->bdi,
-		.sync_mode		= wb->sync_mode,
+		.sync_mode		= sync_mode,
 		.older_than_this	= NULL,
 		.range_cyclic		= 1,
 	};
-	long nr_pages = wb->nr_pages;
 
 	for (;;) {
-		if (wbc.sync_mode == WB_SYNC_NONE && nr_pages <= 0 &&
+		if (sync_mode == WB_SYNC_NONE && nr_pages <= 0 &&
 		    !over_bground_thresh())
 			break;
 
@@ -197,7 +363,7 @@ static void wb_writeback(struct bdi_writeback *wb)
 		wbc.encountered_congestion = 0;
 		wbc.nr_to_write = MAX_WRITEBACK_PAGES;
 		wbc.pages_skipped = 0;
-		generic_sync_wb_inodes(wb, wb->sb, &wbc);
+		generic_sync_wb_inodes(wb, sb, &wbc);
 		nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
 		/*
 		 * If we ran out of stuff to write, bail unless more_io got set
@@ -211,6 +377,82 @@ static void wb_writeback(struct bdi_writeback *wb)
 }
 
 /*
+ * Return the next bdi_work struct that hasn't been processed by this
+ * wb thread yet
+ */
+static struct bdi_work *get_next_work_item(struct backing_dev_info *bdi,
+					   struct bdi_writeback *wb)
+{
+	struct bdi_work *work, *ret = NULL;
+
+	rcu_read_lock();
+
+	list_for_each_entry_rcu(work, &bdi->work_list, list) {
+		if (!test_and_clear_bit(wb->nr, &work->seen))
+			continue;
+
+		ret = work;
+		break;
+	}
+
+	rcu_read_unlock();
+	return ret;
+}
+
+/*
+ * Retrieve work items and do the writeback they describe
+ */
+static void wb_writeback(struct bdi_writeback *wb)
+{
+	struct backing_dev_info *bdi = wb->bdi;
+	struct bdi_work *work;
+
+	while ((work = get_next_work_item(bdi, wb)) != NULL) {
+		struct super_block *sb = bdi_work_sb(work);
+		long nr_pages = work->nr_pages;
+		enum writeback_sync_modes sync_mode = work->sync_mode;
+
+		/*
+		 * If this isn't a data integrity operation, just notify
+		 * that we have seen this work and we are now starting it.
+		 */
+		if (sync_mode == WB_SYNC_NONE)
+			wb_clear_pending(wb, work);
+
+		__wb_writeback(wb, nr_pages, sb, sync_mode);
+
+		/*
+		 * This is a data integrity writeback, so only do the
+		 * notification when we have completed the work.
+		 */
+		if (sync_mode == WB_SYNC_ALL)
+			wb_clear_pending(wb, work);
+	}
+}
+
+/*
+ * This will be inlined in bdi_writeback_task() once we get rid of any
+ * dirty inodes on the default_backing_dev_info
+ */
+void wb_do_writeback(struct bdi_writeback *wb)
+{
+	/*
+	 * We get here in two cases:
+	 *
+	 *  schedule_timeout() returned because the dirty writeback
+	 *  interval has elapsed. If that happens, the work item list
+	 *  will be empty and we will proceed to do kupdated style writeout.
+	 *
+	 *  Someone called bdi_start_writeback(), which put one/more work
+	 *  items on the work_list. Process those.
+	 */
+	if (list_empty(&wb->bdi->work_list))
+		wb_kupdated(wb);
+	else
+		wb_writeback(wb);
+}
+
+/*
  * Handle writeback of dirty data for the device backed by this bdi. Also
  * wakes up periodically and does kupdated style flushing.
  */
@@ -219,49 +461,69 @@ int bdi_writeback_task(struct bdi_writeback *wb)
 	while (!kthread_should_stop()) {
 		unsigned long wait_jiffies;
 
+		wb_do_writeback(wb);
+
 		wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10);
 		set_current_state(TASK_INTERRUPTIBLE);
 		schedule_timeout(wait_jiffies);
 		try_to_freeze();
-
-		/*
-		 * We get here in two cases:
-		 *
-		 *  schedule_timeout() returned because the dirty writeback
-		 *  interval has elapsed. If that happens, we will be able
-		 *  to acquire the writeback lock and will proceed to do
-		 *  kupdated style writeout.
-		 *
-		 *  Someone called bdi_start_writeback(), which will acquire
-		 *  the writeback lock. This means our writeback_acquire()
-		 *  below will fail and we call into bdi_pdflush() for
-		 *  pdflush style writeout.
-		 *
-		 */
-		if (writeback_acquire(wb))
-			wb_kupdated(wb);
-		else
-			wb_writeback(wb);
-
-		writeback_release(wb);
 	}
 
 	return 0;
 }
 
+/*
+ * Schedule writeback for all backing devices. Expensive! If this is a data
+ * integrity operation, writeback will be complete when this returns. If
+ * we are simply called for WB_SYNC_NONE, then writeback will merely be
+ * scheduled to run.
+ */
 void bdi_writeback_all(struct super_block *sb, struct writeback_control *wbc)
 {
+	const bool must_wait = wbc->sync_mode == WB_SYNC_ALL;
 	struct backing_dev_info *bdi, *tmp;
+	struct bdi_work *work;
+	LIST_HEAD(list);
 
 	mutex_lock(&bdi_lock);
 
 	list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
+		struct bdi_work *work;
+
 		if (!bdi_has_dirty_io(bdi))
 			continue;
-		bdi_start_writeback(bdi, sb, wbc->nr_to_write, wbc->sync_mode);
+
+		/*
+		 * If work allocation fails, do the writes inline. An
+		 * alternative approach would be too fall back to an on-stack
+		 * allocation of work. For that we need to drop the bdi_lock
+		 * and restart the scan afterwards, though.
+		 */
+		work = bdi_alloc_work(sb, wbc->nr_to_write, wbc->sync_mode);
+		if (!work) {
+			wbc->bdi = bdi;
+			generic_sync_bdi_inodes(sb, wbc);
+			continue;
+		}
+		if (must_wait)
+			list_add_tail(&work->wait_list, &list);
+
+		bdi_queue_work(bdi, work);
+		__bdi_start_work(bdi, work);
 	}
 
 	mutex_unlock(&bdi_lock);
+
+	/*
+	 * If this is for WB_SYNC_ALL, wait for pending work to complete
+	 * before returning.
+	 */
+	while (!list_empty(&list)) {
+		work = list_entry(list.next, struct bdi_work, wait_list);
+		list_del(&work->wait_list);
+		bdi_wait_on_work_clear(work);
+		call_rcu(&work->rcu_head, bdi_work_free);
+	}
 }
 
 static noinline void block_dump___mark_inode_dirty(struct inode *inode)
@@ -287,11 +549,18 @@ static noinline void block_dump___mark_inode_dirty(struct inode *inode)
 }
 
 /*
- * We have only a single wb per bdi, so just return that.
+ * If the filesystem didn't provide a way to map an inode to a dedicated
+ * flusher thread, it doesn't support more than 1 thread. So we know it's
+ * the default thread, return that.
  */
 static inline struct bdi_writeback *inode_get_wb(struct inode *inode)
 {
-	return &inode_to_bdi(inode)->wb;
+	const struct super_operations *sop = inode->i_sb->s_op;
+
+	if (!sop->inode_get_wb)
+		return &inode_to_bdi(inode)->wb;
+
+	return sop->inode_get_wb(inode);
 }
 
 /**
@@ -728,8 +997,24 @@ void generic_sync_bdi_inodes(struct super_block *sb,
 			     struct writeback_control *wbc)
 {
 	struct backing_dev_info *bdi = wbc->bdi;
+	struct bdi_writeback *wb;
 
-	generic_sync_wb_inodes(&bdi->wb, sb, wbc);
+	/*
+	 * Common case is just a single wb thread and that is embedded in
+	 * the bdi, so it doesn't need locking
+	 */
+	if (!bdi_wblist_needs_lock(bdi))
+		generic_sync_wb_inodes(&bdi->wb, sb, wbc);
+	else {
+		int idx;
+
+		idx = srcu_read_lock(&bdi->srcu);
+
+		list_for_each_entry_rcu(wb, &bdi->wb_list, list)
+			generic_sync_wb_inodes(wb, sb, wbc);
+
+		srcu_read_unlock(&bdi->srcu, idx);
+	}
 }
 
 /*
@@ -756,7 +1041,7 @@ void generic_sync_sb_inodes(struct super_block *sb,
 				struct writeback_control *wbc)
 {
 	if (wbc->bdi)
-		generic_sync_bdi_inodes(sb, wbc);
+		bdi_start_writeback(wbc->bdi, sb, wbc->nr_to_write, wbc->sync_mode);
 	else
 		bdi_writeback_all(sb, wbc);
 
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 1845625..74d29bc 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -13,6 +13,8 @@
 #include <linux/proportions.h>
 #include <linux/kernel.h>
 #include <linux/fs.h>
+#include <linux/sched.h>
+#include <linux/srcu.h>
 #include <linux/writeback.h>
 #include <asm/atomic.h>
 
@@ -26,6 +28,7 @@ struct dentry;
 enum bdi_state {
 	BDI_pending,		/* On its way to being activated */
 	BDI_wb_alloc,		/* Default embedded wb allocated */
+	BDI_wblist_lock,	/* bdi->wb_list now needs locking */
 	BDI_async_congested,	/* The async (write) queue is getting full */
 	BDI_sync_congested,	/* The sync queue is getting full */
 	BDI_unused,		/* Available bits start here */
@@ -42,6 +45,8 @@ enum bdi_stat_item {
 #define BDI_STAT_BATCH (8*(1+ilog2(nr_cpu_ids)))
 
 struct bdi_writeback {
+	struct list_head list;			/* hangs off the bdi */
+
 	struct backing_dev_info *bdi;		/* our parent bdi */
 	unsigned int nr;
 
@@ -49,13 +54,12 @@ struct bdi_writeback {
 	struct list_head	b_dirty;	/* dirty inodes */
 	struct list_head	b_io;		/* parked for writeback */
 	struct list_head	b_more_io;	/* parked for more writeback */
-
-	unsigned long		nr_pages;
-	struct super_block	*sb;
-	enum writeback_sync_modes sync_mode;
 };
 
+#define BDI_MAX_FLUSHERS	32
+
 struct backing_dev_info {
+	struct srcu_struct srcu; /* for wb_list read side protection */
 	struct list_head bdi_list;
 	unsigned long ra_pages;	/* max readahead in PAGE_CACHE_SIZE units */
 	unsigned long state;	/* Always use atomic bitops on this */
@@ -74,8 +78,12 @@ struct backing_dev_info {
 	unsigned int max_ratio, max_prop_frac;
 
 	struct bdi_writeback wb;  /* default writeback info for this bdi */
-	unsigned long wb_active;  /* bitmap of active tasks */
-	unsigned long wb_mask;	  /* number of registered tasks */
+	spinlock_t wb_lock;	  /* protects update side of wb_list */
+	struct list_head wb_list; /* the flusher threads hanging off this bdi */
+	unsigned long wb_mask;	  /* bitmask of registered tasks */
+	unsigned int wb_cnt;	  /* number of registered tasks */
+
+	struct list_head work_list;
 
 	struct device *dev;
 
@@ -92,16 +100,22 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 		const char *fmt, ...);
 int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev);
 void bdi_unregister(struct backing_dev_info *bdi);
-int bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
+void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
 			 long nr_pages, enum writeback_sync_modes sync_mode);
 int bdi_writeback_task(struct bdi_writeback *wb);
 void bdi_writeback_all(struct super_block *sb, struct writeback_control *wbc);
 void bdi_add_default_flusher_task(struct backing_dev_info *bdi);
+void bdi_add_flusher_task(struct backing_dev_info *bdi);
 int bdi_has_dirty_io(struct backing_dev_info *bdi);
 
 extern struct mutex bdi_lock;
 extern struct list_head bdi_list;
 
+static inline int bdi_wblist_needs_lock(struct backing_dev_info *bdi)
+{
+	return test_bit(BDI_wblist_lock, &bdi->state);
+}
+
 static inline int wb_has_dirty_io(struct bdi_writeback *wb)
 {
 	return !list_empty(&wb->b_dirty) ||
@@ -313,4 +327,10 @@ static inline bool mapping_cap_swap_backed(struct address_space *mapping)
 	return bdi_cap_swap_backed(mapping->backing_dev_info);
 }
 
+static inline int bdi_sched_wait(void *word)
+{
+	schedule();
+	return 0;
+}
+
 #endif		/* _LINUX_BACKING_DEV_H */
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 1a8fe89..366aa9d 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1544,11 +1544,14 @@ extern ssize_t vfs_readv(struct file *, const struct iovec __user *,
 extern ssize_t vfs_writev(struct file *, const struct iovec __user *,
 		unsigned long, loff_t *);
 
+struct bdi_writeback;
+
 struct super_operations {
    	struct inode *(*alloc_inode)(struct super_block *sb);
 	void (*destroy_inode)(struct inode *);
 
    	void (*dirty_inode) (struct inode *);
+	struct bdi_writeback *(*inode_get_wb) (struct inode *);
 	int (*write_inode) (struct inode *, int);
 	void (*drop_inode) (struct inode *);
 	void (*delete_inode) (struct inode *);
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 6e416a9..35aee4c 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -68,6 +68,7 @@ struct writeback_control {
 void writeback_inodes(struct writeback_control *wbc);
 int inode_wait(void *);
 void sync_inodes_sb(struct super_block *, int wait);
+void wb_do_writeback(struct bdi_writeback *wb);
 
 /* writeback.h requires fs.h; it, too, is not included from here. */
 static inline void wait_on_inode(struct inode *inode)
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index e6c316a..0a1091d 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -213,52 +213,100 @@ static int __init default_bdi_init(void)
 }
 subsys_initcall(default_bdi_init);
 
-static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
+static int wb_assign_nr(struct backing_dev_info *bdi, struct bdi_writeback *wb)
 {
-	memset(wb, 0, sizeof(*wb));
+	unsigned long mask = BDI_MAX_FLUSHERS - 1;
+	unsigned int nr;
 
-	wb->bdi = bdi;
-	INIT_LIST_HEAD(&wb->b_dirty);
-	INIT_LIST_HEAD(&wb->b_io);
-	INIT_LIST_HEAD(&wb->b_more_io);
-}
+	do {
+		if ((bdi->wb_mask & mask) == mask)
+			return 1;
+
+		nr = find_first_zero_bit(&bdi->wb_mask, BDI_MAX_FLUSHERS);
+	} while (test_and_set_bit(nr, &bdi->wb_mask));
+
+	wb->nr = nr;
+
+	spin_lock(&bdi->wb_lock);
+	bdi->wb_cnt++;
+	spin_unlock(&bdi->wb_lock);
 
-static int wb_assign_nr(struct backing_dev_info *bdi, struct bdi_writeback *wb)
-{
-	set_bit(0, &bdi->wb_mask);
-	wb->nr = 0;
 	return 0;
 }
 
 static void bdi_put_wb(struct backing_dev_info *bdi, struct bdi_writeback *wb)
 {
-	clear_bit(wb->nr, &bdi->wb_mask);
-	clear_bit(BDI_wb_alloc, &bdi->state);
+	/*
+	 * If this is the default wb thread exiting, leave the bit set
+	 * in the wb mask as we set that before it's created as well. This
+	 * is done to make sure that assigned work with no thread has at
+	 * least one receipient.
+	 */
+	if (wb == &bdi->wb)
+		clear_bit(BDI_wb_alloc, &bdi->state);
+	else {
+		clear_bit(wb->nr, &bdi->wb_mask);
+		kfree(wb);
+		spin_lock(&bdi->wb_lock);
+		bdi->wb_cnt--;
+		spin_unlock(&bdi->wb_lock);
+	}
+}
+
+static int bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
+{
+	memset(wb, 0, sizeof(*wb));
+
+	wb->bdi = bdi;
+	INIT_LIST_HEAD(&wb->b_dirty);
+	INIT_LIST_HEAD(&wb->b_io);
+	INIT_LIST_HEAD(&wb->b_more_io);
+
+	return wb_assign_nr(bdi, wb);
 }
 
 static struct bdi_writeback *bdi_new_wb(struct backing_dev_info *bdi)
 {
 	struct bdi_writeback *wb;
 
-	set_bit(BDI_wb_alloc, &bdi->state);
-	wb = &bdi->wb;
-	wb_assign_nr(bdi, wb);
+	/*
+	 * Default bdi->wb is already assigned, so just return it
+	 */
+	if (!test_and_set_bit(BDI_wb_alloc, &bdi->state))
+		wb = &bdi->wb;
+	else {
+		wb = kmalloc(sizeof(struct bdi_writeback), GFP_KERNEL);
+		if (wb) {
+			if (bdi_wb_init(wb, bdi)) {
+				kfree(wb);
+				wb = NULL;
+			}
+		}
+	}
+
 	return wb;
 }
 
-static int bdi_start_fn(void *ptr)
+static void bdi_task_init(struct backing_dev_info *bdi,
+			  struct bdi_writeback *wb)
 {
-	struct bdi_writeback *wb = ptr;
-	struct backing_dev_info *bdi = wb->bdi;
 	struct task_struct *tsk = current;
-	int ret;
+	int was_empty;
 
 	/*
-	 * Add us to the active bdi_list
+	 * Add us to the active bdi_list. If we are adding threads beyond
+	 * the default embedded bdi_writeback, then we need to start using
+	 * proper locking. Check the list for empty first, then set the
+	 * BDI_wblist_lock flag if there's > 1 entry on the list now
 	 */
-	mutex_lock(&bdi_lock);
-	list_add(&bdi->bdi_list, &bdi_list);
-	mutex_unlock(&bdi_lock);
+	spin_lock(&bdi->wb_lock);
+
+	was_empty = list_empty(&bdi->wb_list);
+	list_add_tail_rcu(&wb->list, &bdi->wb_list);
+	if (!was_empty)
+		set_bit(BDI_wblist_lock, &bdi->state);
+
+	spin_unlock(&bdi->wb_lock);
 
 	tsk->flags |= PF_FLUSHER | PF_SWAPWRITE;
 	set_freezable();
@@ -267,6 +315,22 @@ static int bdi_start_fn(void *ptr)
 	 * Our parent may run at a different priority, just set us to normal
 	 */
 	set_user_nice(tsk, 0);
+}
+
+static int bdi_start_fn(void *ptr)
+{
+	struct bdi_writeback *wb = ptr;
+	struct backing_dev_info *bdi = wb->bdi;
+	int ret;
+
+	/*
+	 * Add us to the active bdi_list
+	 */
+	mutex_lock(&bdi_lock);
+	list_add(&bdi->bdi_list, &bdi_list);
+	mutex_unlock(&bdi_lock);
+
+	bdi_task_init(bdi, wb);
 
 	/*
 	 * Clear pending bit and wakeup anybody waiting to tear us down
@@ -277,13 +341,44 @@ static int bdi_start_fn(void *ptr)
 
 	ret = bdi_writeback_task(wb);
 
+	/*
+	 * Remove us from the list
+	 */
+	spin_lock(&bdi->wb_lock);
+	list_del_rcu(&wb->list);
+	spin_unlock(&bdi->wb_lock);
+
+	/*
+	 * wait for rcu grace period to end, so we can free wb
+	 */
+	synchronize_srcu(&bdi->srcu);
+
 	bdi_put_wb(bdi, wb);
 	return ret;
 }
 
 int bdi_has_dirty_io(struct backing_dev_info *bdi)
 {
-	return wb_has_dirty_io(&bdi->wb);
+	struct bdi_writeback *wb;
+	int ret = 0;
+
+	if (!bdi_wblist_needs_lock(bdi))
+		ret = wb_has_dirty_io(&bdi->wb);
+	else {
+		int idx;
+
+		idx = srcu_read_lock(&bdi->srcu);
+
+		list_for_each_entry_rcu(wb, &bdi->wb_list, list) {
+			ret = wb_has_dirty_io(wb);
+			if (ret)
+				break;
+		}
+
+		srcu_read_unlock(&bdi->srcu, idx);
+	}
+
+	return ret;
 }
 
 static void bdi_flush_io(struct backing_dev_info *bdi)
@@ -340,6 +435,8 @@ static int bdi_forker_task(void *ptr)
 {
 	struct bdi_writeback *me = ptr;
 
+	bdi_task_init(me->bdi, me);
+
 	for (;;) {
 		struct backing_dev_info *bdi, *tmp;
 		struct bdi_writeback *wb;
@@ -348,8 +445,8 @@ static int bdi_forker_task(void *ptr)
 		 * 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))
-			bdi_flush_io(me->bdi);
+		if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list))
+			wb_do_writeback(me);
 
 		mutex_lock(&bdi_lock);
 
@@ -420,27 +517,70 @@ readd_flush:
 }
 
 /*
- * Add a new flusher task that gets created for any bdi
- * that has dirty data pending writeout
+ * bdi_lock held on entry
  */
-void bdi_add_default_flusher_task(struct backing_dev_info *bdi)
+static void bdi_add_one_flusher_task(struct backing_dev_info *bdi,
+				     int(*func)(struct backing_dev_info *))
 {
 	if (!bdi_cap_writeback_dirty(bdi))
 		return;
 
 	/*
-	 * Someone already marked this pending for task creation
+	 * Check with the helper whether to proceed adding a task. Will only
+	 * abort if we two or more simultanous calls to
+	 * bdi_add_default_flusher_task() occured, further additions will block
+	 * waiting for previous additions to finish.
 	 */
-	if (test_and_set_bit(BDI_pending, &bdi->state))
-		return;
+	if (!func(bdi)) {
+		list_move_tail(&bdi->bdi_list, &bdi_pending_list);
 
-	mutex_lock(&bdi_lock);
-	list_move_tail(&bdi->bdi_list, &bdi_pending_list);
+		/*
+		 * We are now on the pending list, wake up bdi_forker_task()
+		 * to finish the job and add us back to the active bdi_list
+		 */
+		wake_up_process(default_backing_dev_info.wb.task);
+	}
+}
+
+static int flusher_add_helper_block(struct backing_dev_info *bdi)
+{
 	mutex_unlock(&bdi_lock);
+	wait_on_bit_lock(&bdi->state, BDI_pending, bdi_sched_wait,
+				TASK_UNINTERRUPTIBLE);
+	mutex_lock(&bdi_lock);
+	return 0;
+}
 
-	wake_up_process(default_backing_dev_info.wb.task);
+static int flusher_add_helper_test(struct backing_dev_info *bdi)
+{
+	return test_and_set_bit(BDI_pending, &bdi->state);
+}
+
+/*
+ * Add the default flusher task that gets created for any bdi
+ * that has dirty data pending writeout
+ */
+void bdi_add_default_flusher_task(struct backing_dev_info *bdi)
+{
+	bdi_add_one_flusher_task(bdi, flusher_add_helper_test);
 }
 
+/**
+ * bdi_add_flusher_task - add one more flusher task to this @bdi
+ *  @bdi:	the bdi
+ *
+ * Add an additional flusher task to this @bdi. Will block waiting on
+ * previous additions, if any.
+ *
+ */
+void bdi_add_flusher_task(struct backing_dev_info *bdi)
+{
+	mutex_lock(&bdi_lock);
+	bdi_add_one_flusher_task(bdi, flusher_add_helper_block);
+	mutex_unlock(&bdi_lock);
+}
+EXPORT_SYMBOL(bdi_add_flusher_task);
+
 int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 		const char *fmt, ...)
 {
@@ -504,24 +644,21 @@ int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
 }
 EXPORT_SYMBOL(bdi_register_dev);
 
-static int sched_wait(void *word)
-{
-	schedule();
-	return 0;
-}
-
 /*
  * Remove bdi from global list and shutdown any threads we have running
  */
 static void bdi_wb_shutdown(struct backing_dev_info *bdi)
 {
+	struct bdi_writeback *wb;
+
 	if (!bdi_cap_writeback_dirty(bdi))
 		return;
 
 	/*
 	 * If setup is pending, wait for that to complete first
 	 */
-	wait_on_bit(&bdi->state, BDI_pending, sched_wait, TASK_UNINTERRUPTIBLE);
+	wait_on_bit(&bdi->state, BDI_pending, bdi_sched_wait,
+			TASK_UNINTERRUPTIBLE);
 
 	/*
 	 * Make sure nobody finds us on the bdi_list anymore
@@ -531,9 +668,11 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi)
 	mutex_unlock(&bdi_lock);
 
 	/*
-	 * Finally, kill the kernel thread
+	 * Finally, kill the kernel threads. We don't need to be RCU
+	 * safe anymore, since the bdi is gone from visibility.
 	 */
-	kthread_stop(bdi->wb.task);
+	list_for_each_entry(wb, &bdi->wb_list, list)
+		kthread_stop(wb->task);
 }
 
 void bdi_unregister(struct backing_dev_info *bdi)
@@ -557,8 +696,12 @@ int bdi_init(struct backing_dev_info *bdi)
 	bdi->min_ratio = 0;
 	bdi->max_ratio = 100;
 	bdi->max_prop_frac = PROP_FRAC_BASE;
+	spin_lock_init(&bdi->wb_lock);
+	bdi->wb_mask = 0;
+	bdi->wb_cnt = 0;
 	INIT_LIST_HEAD(&bdi->bdi_list);
-	bdi->wb_mask = bdi->wb_active = 0;
+	INIT_LIST_HEAD(&bdi->wb_list);
+	INIT_LIST_HEAD(&bdi->work_list);
 
 	bdi_wb_init(&bdi->wb, bdi);
 
@@ -568,10 +711,15 @@ int bdi_init(struct backing_dev_info *bdi)
 			goto err;
 	}
 
+	err = init_srcu_struct(&bdi->srcu);
+	if (err)
+		goto err;
+
 	bdi->dirty_exceeded = 0;
 	err = prop_local_init_percpu(&bdi->completions);
 
 	if (err) {
+		cleanup_srcu_struct(&bdi->srcu);
 err:
 		while (i--)
 			percpu_counter_destroy(&bdi->bdi_stat[i]);
@@ -589,6 +737,8 @@ void bdi_destroy(struct backing_dev_info *bdi)
 
 	bdi_unregister(bdi);
 
+	cleanup_srcu_struct(&bdi->srcu);
+
 	for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
 		percpu_counter_destroy(&bdi->bdi_stat[i]);
 
-- 
1.6.3.rc0.1.gf800

[PATCH 09/15] writeback: allow sleepy exit of default writeback task

[Jens Axboe]

Since we do lazy create of default writeback tasks for a bdi, we can
allow sleepy exit if it has been completely idle for 5 minutes.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 fs/fs-writeback.c           |   54 ++++++++++++++++++++++++++++++++++--------
 include/linux/backing-dev.h |    5 ++++
 include/linux/writeback.h   |    2 +-
 3 files changed, 49 insertions(+), 12 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index a652693..02009eb 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -303,10 +303,10 @@ void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
  * 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_kupdated(struct bdi_writeback *wb)
+static long wb_kupdated(struct bdi_writeback *wb)
 {
 	unsigned long oldest_jif;
-	long nr_to_write;
+	long nr_to_write, wrote = 0;
 	struct writeback_control wbc = {
 		.bdi			= wb->bdi,
 		.sync_mode		= WB_SYNC_NONE,
@@ -327,10 +327,13 @@ static void wb_kupdated(struct bdi_writeback *wb)
 		wbc.encountered_congestion = 0;
 		wbc.nr_to_write = MAX_WRITEBACK_PAGES;
 		generic_sync_wb_inodes(wb, NULL, &wbc);
+		wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write;
 		if (wbc.nr_to_write > 0)
 			break;	/* All the old data is written */
 		nr_to_write -= MAX_WRITEBACK_PAGES;
 	}
+
+	return wrote;
 }
 
 static inline bool over_bground_thresh(void)
@@ -343,7 +346,7 @@ static inline bool over_bground_thresh(void)
 		global_page_state(NR_UNSTABLE_NFS) >= background_thresh);
 }
 
-static void __wb_writeback(struct bdi_writeback *wb, long nr_pages,
+static long __wb_writeback(struct bdi_writeback *wb, long nr_pages,
 			   struct super_block *sb,
 			   enum writeback_sync_modes sync_mode)
 {
@@ -353,6 +356,7 @@ static void __wb_writeback(struct bdi_writeback *wb, long nr_pages,
 		.older_than_this	= NULL,
 		.range_cyclic		= 1,
 	};
+	long wrote = 0;
 
 	for (;;) {
 		if (sync_mode == WB_SYNC_NONE && nr_pages <= 0 &&
@@ -365,6 +369,7 @@ static void __wb_writeback(struct bdi_writeback *wb, long nr_pages,
 		wbc.pages_skipped = 0;
 		generic_sync_wb_inodes(wb, sb, &wbc);
 		nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
+		wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write;
 		/*
 		 * If we ran out of stuff to write, bail unless more_io got set
 		 */
@@ -374,6 +379,8 @@ static void __wb_writeback(struct bdi_writeback *wb, long nr_pages,
 			break;
 		}
 	}
+
+	return wrote;
 }
 
 /*
@@ -402,10 +409,11 @@ static struct bdi_work *get_next_work_item(struct backing_dev_info *bdi,
 /*
  * Retrieve work items and do the writeback they describe
  */
-static void wb_writeback(struct bdi_writeback *wb)
+static long wb_writeback(struct bdi_writeback *wb)
 {
 	struct backing_dev_info *bdi = wb->bdi;
 	struct bdi_work *work;
+	long wrote = 0;
 
 	while ((work = get_next_work_item(bdi, wb)) != NULL) {
 		struct super_block *sb = bdi_work_sb(work);
@@ -419,7 +427,7 @@ static void wb_writeback(struct bdi_writeback *wb)
 		if (sync_mode == WB_SYNC_NONE)
 			wb_clear_pending(wb, work);
 
-		__wb_writeback(wb, nr_pages, sb, sync_mode);
+		wrote += __wb_writeback(wb, nr_pages, sb, sync_mode);
 
 		/*
 		 * This is a data integrity writeback, so only do the
@@ -428,14 +436,18 @@ static void wb_writeback(struct bdi_writeback *wb)
 		if (sync_mode == WB_SYNC_ALL)
 			wb_clear_pending(wb, work);
 	}
+
+	return wrote;
 }
 
 /*
  * This will be inlined in bdi_writeback_task() once we get rid of any
  * dirty inodes on the default_backing_dev_info
  */
-void wb_do_writeback(struct bdi_writeback *wb)
+long wb_do_writeback(struct bdi_writeback *wb)
 {
+	long wrote;
+
 	/*
 	 * We get here in two cases:
 	 *
@@ -447,9 +459,11 @@ void wb_do_writeback(struct bdi_writeback *wb)
 	 *  items on the work_list. Process those.
 	 */
 	if (list_empty(&wb->bdi->work_list))
-		wb_kupdated(wb);
+		wrote = wb_kupdated(wb);
 	else
-		wb_writeback(wb);
+		wrote = wb_writeback(wb);
+
+	return wrote;
 }
 
 /*
@@ -458,10 +472,28 @@ void wb_do_writeback(struct bdi_writeback *wb)
  */
 int bdi_writeback_task(struct bdi_writeback *wb)
 {
+	unsigned long last_active = jiffies;
+	unsigned long wait_jiffies = -1UL;
+	long pages_written;
+
 	while (!kthread_should_stop()) {
-		unsigned long wait_jiffies;
+		pages_written = wb_do_writeback(wb);
+
+		if (pages_written)
+			last_active = jiffies;
+		else if (wait_jiffies != -1UL) {
+			unsigned long max_idle;
 
-		wb_do_writeback(wb);
+			/*
+			 * Longest period of inactivity that we tolerate. If we
+			 * see dirty data again later, the task will get
+			 * recreated automatically.
+			 */
+			max_idle = max(5UL * 60 * HZ, wait_jiffies);
+			if (time_after(jiffies, max_idle + last_active) &&
+			    wb_is_default_task(wb))
+				break;
+		}
 
 		wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10);
 		set_current_state(TASK_INTERRUPTIBLE);
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 74d29bc..0659d9f 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -111,6 +111,11 @@ int bdi_has_dirty_io(struct backing_dev_info *bdi);
 extern struct mutex bdi_lock;
 extern struct list_head bdi_list;
 
+static inline int wb_is_default_task(struct bdi_writeback *wb)
+{
+	return wb == &wb->bdi->wb;
+}
+
 static inline int bdi_wblist_needs_lock(struct backing_dev_info *bdi)
 {
 	return test_bit(BDI_wblist_lock, &bdi->state);
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 35aee4c..0d4e31d 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -68,7 +68,7 @@ struct writeback_control {
 void writeback_inodes(struct writeback_control *wbc);
 int inode_wait(void *);
 void sync_inodes_sb(struct super_block *, int wait);
-void wb_do_writeback(struct bdi_writeback *wb);
+long wb_do_writeback(struct bdi_writeback *wb);
 
 /* writeback.h requires fs.h; it, too, is not included from here. */
 static inline void wait_on_inode(struct inode *inode)
-- 
1.6.3.rc0.1.gf800

[PATCH 10/15] writeback: add some debug inode list counters to bdi stats

[Jens Axboe]

Add some debug entries to be able to inspect the internal state of
the writeback details.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 mm/backing-dev.c |   38 ++++++++++++++++++++++++++++++++++----
 1 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 0a1091d..fe5e7b6 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -50,9 +50,29 @@ static void bdi_debug_init(void)
 static int bdi_debug_stats_show(struct seq_file *m, void *v)
 {
 	struct backing_dev_info *bdi = m->private;
+	struct bdi_writeback *wb;
 	unsigned long background_thresh;
 	unsigned long dirty_thresh;
 	unsigned long bdi_thresh;
+	unsigned long nr_dirty, nr_io, nr_more_io, nr_wb;
+	struct inode *inode;
+
+	/*
+	 * inode lock is enough here, the bdi->wb_list is protected by
+	 * RCU on the reader side
+	 */
+	nr_wb = nr_dirty = nr_io = nr_more_io = 0;
+	spin_lock(&inode_lock);
+	list_for_each_entry(wb, &bdi->wb_list, list) {
+		nr_wb++;
+		list_for_each_entry(inode, &wb->b_dirty, i_list)
+			nr_dirty++;
+		list_for_each_entry(inode, &wb->b_io, i_list)
+			nr_io++;
+		list_for_each_entry(inode, &wb->b_more_io, i_list)
+			nr_more_io++;
+	}
+	spin_unlock(&inode_lock);
 
 	get_dirty_limits(&background_thresh, &dirty_thresh, &bdi_thresh, bdi);
 
@@ -62,12 +82,22 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v)
 		   "BdiReclaimable:   %8lu kB\n"
 		   "BdiDirtyThresh:   %8lu kB\n"
 		   "DirtyThresh:      %8lu kB\n"
-		   "BackgroundThresh: %8lu kB\n",
+		   "BackgroundThresh: %8lu kB\n"
+		   "WriteBack threads:%8lu\n"
+		   "b_dirty:          %8lu\n"
+		   "b_io:             %8lu\n"
+		   "b_more_io:        %8lu\n"
+		   "bdi_list:         %8u\n"
+		   "state:            %8lx\n"
+		   "wb_mask:          %8lx\n"
+		   "wb_list:          %8u\n"
+		   "wb_cnt:           %8u\n",
 		   (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));
+		   K(bdi_thresh), K(dirty_thresh),
+		   K(background_thresh), nr_wb, nr_dirty, nr_io, nr_more_io,
+		   !list_empty(&bdi->bdi_list), bdi->state, bdi->wb_mask,
+		   !list_empty(&bdi->wb_list), bdi->wb_cnt);
 #undef K
 
 	return 0;
-- 
1.6.3.rc0.1.gf800

[PATCH 11/15] writeback: add name to backing_dev_info

[Jens Axboe]

This enables us to track who does what and print info. Its main use
is catching dirty inodes on the default_backing_dev_info, so we can
fix that up.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 block/blk-core.c            |    1 +
 drivers/block/aoe/aoeblk.c  |    1 +
 drivers/char/mem.c          |    1 +
 fs/btrfs/disk-io.c          |    1 +
 fs/char_dev.c               |    1 +
 fs/configfs/inode.c         |    1 +
 fs/fuse/inode.c             |    1 +
 fs/hugetlbfs/inode.c        |    1 +
 fs/nfs/client.c             |    1 +
 fs/ocfs2/dlm/dlmfs.c        |    1 +
 fs/ramfs/inode.c            |    1 +
 fs/sysfs/inode.c            |    1 +
 fs/ubifs/super.c            |    1 +
 include/linux/backing-dev.h |    2 ++
 kernel/cgroup.c             |    1 +
 mm/backing-dev.c            |    1 +
 mm/swap_state.c             |    1 +
 17 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 94d88fa..9da9968 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -502,6 +502,7 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
 			(VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
 	q->backing_dev_info.state = 0;
 	q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
+	q->backing_dev_info.name = "block";
 
 	err = bdi_init(&q->backing_dev_info);
 	if (err) {
diff --git a/drivers/block/aoe/aoeblk.c b/drivers/block/aoe/aoeblk.c
index 2307a27..0efb8fc 100644
--- a/drivers/block/aoe/aoeblk.c
+++ b/drivers/block/aoe/aoeblk.c
@@ -265,6 +265,7 @@ aoeblk_gdalloc(void *vp)
 	}
 
 	blk_queue_make_request(&d->blkq, aoeblk_make_request);
+	d->blkq.backing_dev_info.name = "aoe";
 	if (bdi_init(&d->blkq.backing_dev_info))
 		goto err_mempool;
 	spin_lock_irqsave(&d->lock, flags);
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index f96d0be..e5a1e77 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -822,6 +822,7 @@ static const struct file_operations zero_fops = {
  * - permits private mappings, "copies" are taken of the source of zeros
  */
 static struct backing_dev_info zero_bdi = {
+	.name		= "char/mem",
 	.capabilities	= BDI_CAP_MAP_COPY,
 };
 
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index d28d29c..027c8d3 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1352,6 +1352,7 @@ static int setup_bdi(struct btrfs_fs_info *info, struct backing_dev_info *bdi)
 {
 	int err;
 
+	bdi->name = "btrfs";
 	bdi->capabilities = BDI_CAP_MAP_COPY;
 	err = bdi_init(bdi);
 	if (err)
diff --git a/fs/char_dev.c b/fs/char_dev.c
index b7c9d51..a8514ad 100644
--- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -32,6 +32,7 @@
  * - no readahead or I/O queue unplugging required
  */
 struct backing_dev_info directly_mappable_cdev_bdi = {
+	.name = "char",
 	.capabilities	= (
 #ifdef CONFIG_MMU
 		/* permit private copies of the data to be taken */
diff --git a/fs/configfs/inode.c b/fs/configfs/inode.c
index 5d349d3..9a266cd 100644
--- a/fs/configfs/inode.c
+++ b/fs/configfs/inode.c
@@ -46,6 +46,7 @@ static const struct address_space_operations configfs_aops = {
 };
 
 static struct backing_dev_info configfs_backing_dev_info = {
+	.name		= "configfs",
 	.ra_pages	= 0,	/* No readahead */
 	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,
 };
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 91f7c85..e5e8b03 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -484,6 +484,7 @@ int fuse_conn_init(struct fuse_conn *fc, struct super_block *sb)
 	INIT_LIST_HEAD(&fc->bg_queue);
 	INIT_LIST_HEAD(&fc->entry);
 	atomic_set(&fc->num_waiting, 0);
+	fc->bdi.name = "fuse";
 	fc->bdi.ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
 	fc->bdi.unplug_io_fn = default_unplug_io_fn;
 	/* fuse does it's own writeback accounting */
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 941c842..2d8abaf 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -44,6 +44,7 @@ static const struct inode_operations hugetlbfs_dir_inode_operations;
 static const struct inode_operations hugetlbfs_inode_operations;
 
 static struct backing_dev_info hugetlbfs_backing_dev_info = {
+	.name		= "hugetlbfs",
 	.ra_pages	= 0,	/* No readahead */
 	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,
 };
diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index 75c9cd2..3a26d06 100644
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -836,6 +836,7 @@ static void nfs_server_set_fsinfo(struct nfs_server *server, struct nfs_fsinfo *
 		server->rsize = NFS_MAX_FILE_IO_SIZE;
 	server->rpages = (server->rsize + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
 
+	server->backing_dev_info.name = "nfs";
 	server->backing_dev_info.ra_pages = server->rpages * NFS_MAX_READAHEAD;
 
 	if (server->wsize > max_rpc_payload)
diff --git a/fs/ocfs2/dlm/dlmfs.c b/fs/ocfs2/dlm/dlmfs.c
index 1c9efb4..02bf178 100644
--- a/fs/ocfs2/dlm/dlmfs.c
+++ b/fs/ocfs2/dlm/dlmfs.c
@@ -325,6 +325,7 @@ clear_fields:
 }
 
 static struct backing_dev_info dlmfs_backing_dev_info = {
+	.name		= "ocfs2-dlmfs",
 	.ra_pages	= 0,	/* No readahead */
 	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,
 };
diff --git a/fs/ramfs/inode.c b/fs/ramfs/inode.c
index 3a6b193..5a24199 100644
--- a/fs/ramfs/inode.c
+++ b/fs/ramfs/inode.c
@@ -46,6 +46,7 @@ static const struct super_operations ramfs_ops;
 static const struct inode_operations ramfs_dir_inode_operations;
 
 static struct backing_dev_info ramfs_backing_dev_info = {
+	.name		= "ramfs",
 	.ra_pages	= 0,	/* No readahead */
 	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK |
 			  BDI_CAP_MAP_DIRECT | BDI_CAP_MAP_COPY |
diff --git a/fs/sysfs/inode.c b/fs/sysfs/inode.c
index 555f0ff..e57f98e 100644
--- a/fs/sysfs/inode.c
+++ b/fs/sysfs/inode.c
@@ -29,6 +29,7 @@ static const struct address_space_operations sysfs_aops = {
 };
 
 static struct backing_dev_info sysfs_backing_dev_info = {
+	.name		= "sysfs",
 	.ra_pages	= 0,	/* No readahead */
 	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,
 };
diff --git a/fs/ubifs/super.c b/fs/ubifs/super.c
index 3260b73..fcd0240 100644
--- a/fs/ubifs/super.c
+++ b/fs/ubifs/super.c
@@ -1932,6 +1932,7 @@ static int ubifs_fill_super(struct super_block *sb, void *data, int silent)
 	 *
 	 * Read-ahead will be disabled because @c->bdi.ra_pages is 0.
 	 */
+	c->bdi.name = "ubifs",
 	c->bdi.capabilities = BDI_CAP_MAP_COPY;
 	c->bdi.unplug_io_fn = default_unplug_io_fn;
 	err  = bdi_init(&c->bdi);
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 0659d9f..4f07282 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -69,6 +69,8 @@ struct backing_dev_info {
 	void (*unplug_io_fn)(struct backing_dev_info *, struct page *);
 	void *unplug_io_data;
 
+	char *name;
+
 	struct percpu_counter bdi_stat[NR_BDI_STAT_ITEMS];
 
 	struct prop_local_percpu completions;
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 3fb789f..fefa884 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -599,6 +599,7 @@ static struct inode_operations cgroup_dir_inode_operations;
 static struct file_operations proc_cgroupstats_operations;
 
 static struct backing_dev_info cgroup_backing_dev_info = {
+	.name		= "cgroup",
 	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,
 };
 
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index fe5e7b6..efa9726 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -17,6 +17,7 @@ void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
 EXPORT_SYMBOL(default_unplug_io_fn);
 
 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,
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 1416e7e..f1812d7 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -34,6 +34,7 @@ static const struct address_space_operations swap_aops = {
 };
 
 static struct backing_dev_info swap_backing_dev_info = {
+	.name		= "swap",
 	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
 	.unplug_io_fn	= swap_unplug_io_fn,
 };
-- 
1.6.3.rc0.1.gf800

[PATCH 12/15] writeback: check for registered bdi in flusher add and inode dirty

[Jens Axboe]

Also a debugging aid. We want to catch dirty inodes being added to
backing devices that don't do writeback.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 fs/fs-writeback.c           |    7 +++++++
 include/linux/backing-dev.h |    1 +
 mm/backing-dev.c            |    6 ++++++
 3 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 02009eb..65ca410 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -679,6 +679,13 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 		 */
 		if (!was_dirty) {
 			struct bdi_writeback *wb = inode_get_wb(inode);
+			struct backing_dev_info *bdi = wb->bdi;
+
+			if (bdi_cap_writeback_dirty(bdi) &&
+			    !test_bit(BDI_registered, &bdi->state)) {
+				WARN_ON(1);
+				printk("bdi-%s not registered\n", bdi->name);
+			}
 
 			inode->dirtied_when = jiffies;
 			list_move(&inode->i_list, &wb->b_dirty);
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 4f07282..ef7d904 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -31,6 +31,7 @@ enum bdi_state {
 	BDI_wblist_lock,	/* bdi->wb_list now needs locking */
 	BDI_async_congested,	/* The async (write) queue is getting full */
 	BDI_sync_congested,	/* The sync queue is getting full */
+	BDI_registered,		/* bdi_register() was done */
 	BDI_unused,		/* Available bits start here */
 };
 
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index efa9726..18d1194 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -556,6 +556,11 @@ static void bdi_add_one_flusher_task(struct backing_dev_info *bdi,
 	if (!bdi_cap_writeback_dirty(bdi))
 		return;
 
+	if (WARN_ON(!test_bit(BDI_registered, &bdi->state))) {
+		printk("bdi %p/%s is not registered!\n", bdi, bdi->name);
+		return;
+	}
+
 	/*
 	 * Check with the helper whether to proceed adding a task. Will only
 	 * abort if we two or more simultanous calls to
@@ -664,6 +669,7 @@ remove_err:
 	}
 
 	bdi_debug_register(bdi, dev_name(dev));
+	set_bit(BDI_registered, &bdi->state);
 exit:
 	return ret;
 }
-- 
1.6.3.rc0.1.gf800

[PATCH 13/15] writeback: restart bdi list scan on allocation failure

[Jens Axboe]

It's should essentially almost never trigger, so it doesn't matter
if we just restart the scan and potentially do a bit more IO in
this case. And then we can drop bdi_lock before going into inode
sync.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 fs/fs-writeback.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 65ca410..d646e02 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -517,6 +517,7 @@ void bdi_writeback_all(struct super_block *sb, struct writeback_control *wbc)
 	struct bdi_work *work;
 	LIST_HEAD(list);
 
+restart:
 	mutex_lock(&bdi_lock);
 
 	list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
@@ -533,9 +534,13 @@ void bdi_writeback_all(struct super_block *sb, struct writeback_control *wbc)
 		 */
 		work = bdi_alloc_work(sb, wbc->nr_to_write, wbc->sync_mode);
 		if (!work) {
+			if (!must_wait)
+				continue;
+
+			mutex_unlock(&bdi_lock);
 			wbc->bdi = bdi;
 			generic_sync_bdi_inodes(sb, wbc);
-			continue;
+			goto restart;
 		}
 		if (must_wait)
 			list_add_tail(&work->wait_list, &list);
-- 
1.6.3.rc0.1.gf800

[PATCH 14/15] writeback: convert bdi_lock to a spinlock

[Jens Axboe]

We don't sleep under this lock anymore, so make it a spinlock instead.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 fs/fs-writeback.c           |   10 +++++-----
 include/linux/backing-dev.h |    2 +-
 mm/backing-dev.c            |   36 ++++++++++++++++++------------------
 mm/page-writeback.c         |    8 ++++----
 4 files changed, 28 insertions(+), 28 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index d646e02..e15a3fa 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -216,9 +216,9 @@ static void bdi_start_work(struct backing_dev_info *bdi, struct bdi_work *work)
 	 * it gets created and wakes up, we'll run this work.
 	 */
 	if (unlikely(list_empty_careful(&bdi->wb_list))) {
-		mutex_lock(&bdi_lock);
+		spin_lock(&bdi_lock);
 		bdi_add_default_flusher_task(bdi);
-		mutex_unlock(&bdi_lock);
+		spin_unlock(&bdi_lock);
 	} else
 		bdi_sched_work(bdi, work);
 }
@@ -518,7 +518,7 @@ void bdi_writeback_all(struct super_block *sb, struct writeback_control *wbc)
 	LIST_HEAD(list);
 
 restart:
-	mutex_lock(&bdi_lock);
+	spin_lock(&bdi_lock);
 
 	list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
 		struct bdi_work *work;
@@ -537,7 +537,7 @@ restart:
 			if (!must_wait)
 				continue;
 
-			mutex_unlock(&bdi_lock);
+			spin_unlock(&bdi_lock);
 			wbc->bdi = bdi;
 			generic_sync_bdi_inodes(sb, wbc);
 			goto restart;
@@ -549,7 +549,7 @@ restart:
 		__bdi_start_work(bdi, work);
 	}
 
-	mutex_unlock(&bdi_lock);
+	spin_unlock(&bdi_lock);
 
 	/*
 	 * If this is for WB_SYNC_ALL, wait for pending work to complete
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index ef7d904..6815f8b 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -111,7 +111,7 @@ void bdi_add_default_flusher_task(struct backing_dev_info *bdi);
 void bdi_add_flusher_task(struct backing_dev_info *bdi);
 int bdi_has_dirty_io(struct backing_dev_info *bdi);
 
-extern struct mutex bdi_lock;
+extern spinlock_t bdi_lock;
 extern struct list_head bdi_list;
 
 static inline int wb_is_default_task(struct bdi_writeback *wb)
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 18d1194..b3e80c5 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -26,7 +26,7 @@ struct backing_dev_info default_backing_dev_info = {
 EXPORT_SYMBOL_GPL(default_backing_dev_info);
 
 static struct class *bdi_class;
-DEFINE_MUTEX(bdi_lock);
+DEFINE_SPINLOCK(bdi_lock);
 LIST_HEAD(bdi_list);
 LIST_HEAD(bdi_pending_list);
 
@@ -357,9 +357,9 @@ static int bdi_start_fn(void *ptr)
 	/*
 	 * Add us to the active bdi_list
 	 */
-	mutex_lock(&bdi_lock);
+	spin_lock(&bdi_lock);
 	list_add(&bdi->bdi_list, &bdi_list);
-	mutex_unlock(&bdi_lock);
+	spin_unlock(&bdi_lock);
 
 	bdi_task_init(bdi, wb);
 
@@ -479,7 +479,7 @@ static int bdi_forker_task(void *ptr)
 		if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list))
 			wb_do_writeback(me);
 
-		mutex_lock(&bdi_lock);
+		spin_lock(&bdi_lock);
 
 		/*
 		 * Check if any existing bdi's have dirty data without
@@ -497,7 +497,7 @@ static int bdi_forker_task(void *ptr)
 		if (list_empty(&bdi_pending_list)) {
 			unsigned long wait;
 
-			mutex_unlock(&bdi_lock);
+			spin_unlock(&bdi_lock);
 			wait = msecs_to_jiffies(dirty_writeback_interval * 10);
 			schedule_timeout(wait);
 			try_to_freeze();
@@ -513,7 +513,7 @@ static int bdi_forker_task(void *ptr)
 		bdi = list_entry(bdi_pending_list.next, struct backing_dev_info,
 				 bdi_list);
 		list_del_init(&bdi->bdi_list);
-		mutex_unlock(&bdi_lock);
+		spin_unlock(&bdi_lock);
 
 		wb = bdi_new_wb(bdi);
 		if (!wb)
@@ -536,9 +536,9 @@ readd_flush:
 			 * a chance to flush other bdi's to free
 			 * memory.
 			 */
-			mutex_lock(&bdi_lock);
+			spin_lock(&bdi_lock);
 			list_add_tail(&bdi->bdi_list, &bdi_pending_list);
-			mutex_unlock(&bdi_lock);
+			spin_unlock(&bdi_lock);
 
 			bdi_flush_io(bdi);
 		}
@@ -580,10 +580,10 @@ static void bdi_add_one_flusher_task(struct backing_dev_info *bdi,
 
 static int flusher_add_helper_block(struct backing_dev_info *bdi)
 {
-	mutex_unlock(&bdi_lock);
+	spin_unlock(&bdi_lock);
 	wait_on_bit_lock(&bdi->state, BDI_pending, bdi_sched_wait,
 				TASK_UNINTERRUPTIBLE);
-	mutex_lock(&bdi_lock);
+	spin_lock(&bdi_lock);
 	return 0;
 }
 
@@ -611,9 +611,9 @@ void bdi_add_default_flusher_task(struct backing_dev_info *bdi)
  */
 void bdi_add_flusher_task(struct backing_dev_info *bdi)
 {
-	mutex_lock(&bdi_lock);
+	spin_lock(&bdi_lock);
 	bdi_add_one_flusher_task(bdi, flusher_add_helper_block);
-	mutex_unlock(&bdi_lock);
+	spin_unlock(&bdi_lock);
 }
 EXPORT_SYMBOL(bdi_add_flusher_task);
 
@@ -635,9 +635,9 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 		goto exit;
 	}
 
-	mutex_lock(&bdi_lock);
+	spin_lock(&bdi_lock);
 	list_add_tail(&bdi->bdi_list, &bdi_list);
-	mutex_unlock(&bdi_lock);
+	spin_unlock(&bdi_lock);
 
 	bdi->dev = dev;
 
@@ -661,9 +661,9 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 			bdi_put_wb(bdi, wb);
 			ret = -ENOMEM;
 remove_err:
-			mutex_lock(&bdi_lock);
+			spin_lock(&bdi_lock);
 			list_del(&bdi->bdi_list);
-			mutex_unlock(&bdi_lock);
+			spin_unlock(&bdi_lock);
 			goto exit;
 		}
 	}
@@ -700,9 +700,9 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi)
 	/*
 	 * Make sure nobody finds us on the bdi_list anymore
 	 */
-	mutex_lock(&bdi_lock);
+	spin_lock(&bdi_lock);
 	list_del(&bdi->bdi_list);
-	mutex_unlock(&bdi_lock);
+	spin_unlock(&bdi_lock);
 
 	/*
 	 * Finally, kill the kernel threads. We don't need to be RCU
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 91c8615..b5f7110 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -314,7 +314,7 @@ int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
 {
 	int ret = 0;
 
-	mutex_lock(&bdi_lock);
+	spin_lock(&bdi_lock);
 	if (min_ratio > bdi->max_ratio) {
 		ret = -EINVAL;
 	} else {
@@ -326,7 +326,7 @@ int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
 			ret = -EINVAL;
 		}
 	}
-	mutex_unlock(&bdi_lock);
+	spin_unlock(&bdi_lock);
 
 	return ret;
 }
@@ -338,14 +338,14 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
 	if (max_ratio > 100)
 		return -EINVAL;
 
-	mutex_lock(&bdi_lock);
+	spin_lock(&bdi_lock);
 	if (bdi->min_ratio > max_ratio) {
 		ret = -EINVAL;
 	} else {
 		bdi->max_ratio = max_ratio;
 		bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
 	}
-	mutex_unlock(&bdi_lock);
+	spin_unlock(&bdi_lock);
 
 	return ret;
 }
-- 
1.6.3.rc0.1.gf800

[PATCH 15/15] writeback: use spin_trylock() in bdi_writeback_all() for WB_SYNC_NONE

[Jens Axboe]

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 fs/fs-writeback.c |   13 +++++++++++--
 1 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index e15a3fa..98bac71 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -517,9 +517,17 @@ void bdi_writeback_all(struct super_block *sb, struct writeback_control *wbc)
 	struct bdi_work *work;
 	LIST_HEAD(list);
 
-restart:
-	spin_lock(&bdi_lock);
+	/*
+	 * If this isn't a data integrity writeback, just drop it if
+	 * someone is already holding the bdi_lock
+	 */
+	if (!spin_trylock(&bdi_lock)) {
+		if (!must_wait)
+			return;
+		spin_lock(&bdi_lock);
+	}
 
+restart:
 	list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
 		struct bdi_work *work;
 
@@ -540,6 +548,7 @@ restart:
 			spin_unlock(&bdi_lock);
 			wbc->bdi = bdi;
 			generic_sync_bdi_inodes(sb, wbc);
+			spin_lock(&bdi_lock);
 			goto restart;
 		}
 		if (must_wait)
-- 
1.6.3.rc0.1.gf800

Re: [PATCH 0/15] Per-bdi writeback flusher threads v10

[Zhang, Yanmin]

[-- Attachment #1: Type: text/plain, Size: 4076 bytes --]

On Fri, 2009-06-12 at 14:54 +0200, Jens Axboe wrote:
> Hi,
> 
> Here's the 10th version of the writeback patches. Changes since v9:
> 
> - Fix bdi task exit race leaving work on the list, flush it after we
>   know we cannot be found anymore.
> - Rename flusher tasks from bdi-foo to flush-foo. Should make it more
>   clear to the casual observer.
> - Fix a problem with the btrfs bdi register patch that would spew
>   warnings for > 1 mounted btrfs file system.
> - Rebase to current -git, there were some conflicts with the latest work
>   from viro/hch.
> - Fix a block layer core problem were stacked devices would overwrite
>   the bdi state, causing problems and warning spew.
> - In bdi_writeback_all(), in the race occurence of a work allocation
>   failure, restart scanning from the beginning. Then we can drop the
>   bdi_lock mutex before diving into bdi specific writeback.
> - Convert bdi_lock to a spinlock.
> - Use spin_trylock() in bdi_writeback_all(), if this isn't a data
>   integrity writeback. Debatable, I kind of like it...
> - Get rid of BDI_CAP_FLUSH_FORKER, just check for match with the
>   default_backing_dev_info.
> - Fix race in list checking in bdi_forker_task().
> 
> 
> For ease of patching, I've put the full diff here:
> 
>   http://kernel.dk/writeback-v10.patch
Jens,

I applied the patch to 2.6.30 and got a confliction. The attachment is
the patch I ported to 2.6.30. Did I miss anything?


With the patch, kernel reports below messages on 2 machines.

INFO: task sync:29984 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
sync          D ffff88002805e300  6168 29984  24581
 ffff88022f84b780 0000000000000082 7fffffffffffffff ffff880133dbfe70
 0000000000000000 ffff88022e2b4c50 ffff88022e2b4fd8 00000001000c7bb8
 ffff88022f513fd0 ffff880133dbfde8 ffff880133dbfec8 ffff88022d5d13c8
Call Trace:
 [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
 [<ffffffff80780fde>] ? schedule+0x9/0x1d
 [<ffffffff802b69ed>] ? bdi_sched_wait+0x9/0xd
 [<ffffffff8078158d>] ? __wait_on_bit+0x40/0x6f
 [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
 [<ffffffff80781628>] ? out_of_line_wait_on_bit+0x6c/0x78
 [<ffffffff8024a426>] ? wake_bit_function+0x0/0x23
 [<ffffffff802b67ac>] ? bdi_writeback_all+0x12a/0x152
 [<ffffffff802b6805>] ? generic_sync_sb_inodes+0x31/0xde
 [<ffffffff802b6935>] ? sync_inodes_sb+0x83/0x88
 [<ffffffff802b6980>] ? __sync_inodes+0x46/0x8f
 [<ffffffff802b94f2>] ? do_sync+0x36/0x5a
 [<ffffffff802b9538>] ? sys_sync+0xe/0x12
 [<ffffffff8020b9ab>] ? system_call_fastpath+0x16/0x1b

> 
> and also stored this in a writeback-v10 branch that will not change,
> you can pull that into Linus tree from here:
> 
>   git://git.kernel.dk/linux-2.6-block.git writeback-v10
> 
> Please test and report results/interesting finds. Thanks!
> 
>  b/block/blk-core.c            |    6 
>  b/block/blk-settings.c        |    4 
>  b/drivers/block/aoe/aoeblk.c  |    1 
>  b/drivers/char/mem.c          |    1 
>  b/fs/btrfs/disk-io.c          |   27 -
>  b/fs/buffer.c                 |    2 
>  b/fs/char_dev.c               |    1 
>  b/fs/configfs/inode.c         |    1 
>  b/fs/fs-writeback.c           |  818 +++++++++++++++++++++++++++-------
>  b/fs/fuse/inode.c             |    1 
>  b/fs/hugetlbfs/inode.c        |    1 
>  b/fs/nfs/client.c             |    1 
>  b/fs/ocfs2/dlm/dlmfs.c        |    1 
>  b/fs/ramfs/inode.c            |    1 
>  b/fs/super.c                  |    3 
>  b/fs/sysfs/inode.c            |    1 
>  b/fs/ubifs/super.c            |    4 
>  b/include/linux/backing-dev.h |   72 ++
>  b/include/linux/fs.h          |   11 
>  b/include/linux/writeback.h   |   15 
>  b/kernel/cgroup.c             |    1 
>  b/mm/Makefile                 |    2 
>  b/mm/backing-dev.c            |  519 +++++++++++++++++++++
>  b/mm/page-writeback.c         |  157 ------
>  b/mm/swap_state.c             |    1 
>  b/mm/vmscan.c                 |    2 
>  mm/pdflush.c                  |  269 -----------
>  27 files changed, 1317 insertions(+), 606 deletions(-)
> 

[-- Attachment #2: writeback-v10_port.patch --]
[-- Type: text/x-patch, Size: 82831 bytes --]

diff -Nraup linux-2.6.30/block/blk-core.c linux-2.6.30_bdiflusherv10/block/blk-core.c
--- linux-2.6.30/block/blk-core.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/block/blk-core.c	2009-06-15 15:52:50.000000000 +0800
@@ -517,6 +517,12 @@ struct request_queue *blk_alloc_queue_no
 
 	q->backing_dev_info.unplug_io_fn = blk_backing_dev_unplug;
 	q->backing_dev_info.unplug_io_data = q;
+	q->backing_dev_info.ra_pages =
+			(VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
+	q->backing_dev_info.state = 0;
+	q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
+	q->backing_dev_info.name = "block";
+
 	err = bdi_init(&q->backing_dev_info);
 	if (err) {
 		kmem_cache_free(blk_requestq_cachep, q);
diff -Nraup linux-2.6.30/block/blk-settings.c linux-2.6.30_bdiflusherv10/block/blk-settings.c
--- linux-2.6.30/block/blk-settings.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/block/blk-settings.c	2009-06-15 15:52:50.000000000 +0800
@@ -129,10 +129,6 @@ void blk_queue_make_request(struct reque
 	blk_queue_max_segment_size(q, MAX_SEGMENT_SIZE);
 
 	q->make_request_fn = mfn;
-	q->backing_dev_info.ra_pages =
-			(VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
-	q->backing_dev_info.state = 0;
-	q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
 	blk_queue_max_sectors(q, SAFE_MAX_SECTORS);
 	blk_queue_hardsect_size(q, 512);
 	blk_queue_dma_alignment(q, 511);
diff -Nraup linux-2.6.30/drivers/block/aoe/aoeblk.c linux-2.6.30_bdiflusherv10/drivers/block/aoe/aoeblk.c
--- linux-2.6.30/drivers/block/aoe/aoeblk.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/drivers/block/aoe/aoeblk.c	2009-06-15 15:52:50.000000000 +0800
@@ -265,6 +265,7 @@ aoeblk_gdalloc(void *vp)
 	}
 
 	blk_queue_make_request(&d->blkq, aoeblk_make_request);
+	d->blkq.backing_dev_info.name = "aoe";
 	if (bdi_init(&d->blkq.backing_dev_info))
 		goto err_mempool;
 	spin_lock_irqsave(&d->lock, flags);
diff -Nraup linux-2.6.30/drivers/char/mem.c linux-2.6.30_bdiflusherv10/drivers/char/mem.c
--- linux-2.6.30/drivers/char/mem.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/drivers/char/mem.c	2009-06-15 15:52:50.000000000 +0800
@@ -823,6 +823,7 @@ static const struct file_operations zero
  * - permits private mappings, "copies" are taken of the source of zeros
  */
 static struct backing_dev_info zero_bdi = {
+	.name		= "char/mem",
 	.capabilities	= BDI_CAP_MAP_COPY,
 };
 
diff -Nraup linux-2.6.30/fs/btrfs/disk-io.c linux-2.6.30_bdiflusherv10/fs/btrfs/disk-io.c
--- linux-2.6.30/fs/btrfs/disk-io.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/fs/btrfs/disk-io.c	2009-06-15 15:52:50.000000000 +0800
@@ -43,6 +43,8 @@
 static struct extent_io_ops btree_extent_io_ops;
 static void end_workqueue_fn(struct btrfs_work *work);
 
+static atomic_t btrfs_bdi_num = ATOMIC_INIT(0);
+
 /*
  * end_io_wq structs are used to do processing in task context when an IO is
  * complete.  This is used during reads to verify checksums, and it is used
@@ -1345,12 +1347,26 @@ static void btrfs_unplug_io_fn(struct ba
 	free_extent_map(em);
 }
 
+/*
+ * If this fails, caller must call bdi_destroy() to get rid of the
+ * bdi again.
+ */
 static int setup_bdi(struct btrfs_fs_info *info, struct backing_dev_info *bdi)
 {
-	bdi_init(bdi);
+	int err;
+
+	bdi->name = "btrfs";
+	bdi->capabilities = BDI_CAP_MAP_COPY;
+	err = bdi_init(bdi);
+	if (err)
+		return err;
+
+	err = bdi_register(bdi, NULL, "btrfs-%d",
+				atomic_inc_return(&btrfs_bdi_num));
+	if (err)
+		return err;
+
 	bdi->ra_pages	= default_backing_dev_info.ra_pages;
-	bdi->state		= 0;
-	bdi->capabilities	= default_backing_dev_info.capabilities;
 	bdi->unplug_io_fn	= btrfs_unplug_io_fn;
 	bdi->unplug_io_data	= info;
 	bdi->congested_fn	= btrfs_congested_fn;
@@ -1574,7 +1590,8 @@ struct btrfs_root *open_ctree(struct sup
 	fs_info->sb = sb;
 	fs_info->max_extent = (u64)-1;
 	fs_info->max_inline = 8192 * 1024;
-	setup_bdi(fs_info, &fs_info->bdi);
+	if (setup_bdi(fs_info, &fs_info->bdi))
+		goto fail_bdi;
 	fs_info->btree_inode = new_inode(sb);
 	fs_info->btree_inode->i_ino = 1;
 	fs_info->btree_inode->i_nlink = 1;
@@ -1931,8 +1948,8 @@ fail_iput:
 
 	btrfs_close_devices(fs_info->fs_devices);
 	btrfs_mapping_tree_free(&fs_info->mapping_tree);
+fail_bdi:
 	bdi_destroy(&fs_info->bdi);
-
 fail:
 	kfree(extent_root);
 	kfree(tree_root);
diff -Nraup linux-2.6.30/fs/buffer.c linux-2.6.30_bdiflusherv10/fs/buffer.c
--- linux-2.6.30/fs/buffer.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/fs/buffer.c	2009-06-15 15:52:50.000000000 +0800
@@ -281,7 +281,7 @@ static void free_more_memory(void)
 	struct zone *zone;
 	int nid;
 
-	wakeup_pdflush(1024);
+	wakeup_flusher_threads(1024);
 	yield();
 
 	for_each_online_node(nid) {
diff -Nraup linux-2.6.30/fs/char_dev.c linux-2.6.30_bdiflusherv10/fs/char_dev.c
--- linux-2.6.30/fs/char_dev.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/fs/char_dev.c	2009-06-15 15:52:50.000000000 +0800
@@ -32,6 +32,7 @@
  * - no readahead or I/O queue unplugging required
  */
 struct backing_dev_info directly_mappable_cdev_bdi = {
+	.name = "char",
 	.capabilities	= (
 #ifdef CONFIG_MMU
 		/* permit private copies of the data to be taken */
diff -Nraup linux-2.6.30/fs/configfs/inode.c linux-2.6.30_bdiflusherv10/fs/configfs/inode.c
--- linux-2.6.30/fs/configfs/inode.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/fs/configfs/inode.c	2009-06-15 15:52:50.000000000 +0800
@@ -46,6 +46,7 @@ static const struct address_space_operat
 };
 
 static struct backing_dev_info configfs_backing_dev_info = {
+	.name		= "configfs",
 	.ra_pages	= 0,	/* No readahead */
 	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,
 };
diff -Nraup linux-2.6.30/fs/fs-writeback.c linux-2.6.30_bdiflusherv10/fs/fs-writeback.c
--- linux-2.6.30/fs/fs-writeback.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/fs/fs-writeback.c	2009-06-15 15:52:50.000000000 +0800
@@ -19,49 +19,572 @@
 #include <linux/sched.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
+#include <linux/kthread.h>
+#include <linux/freezer.h>
 #include <linux/writeback.h>
 #include <linux/blkdev.h>
 #include <linux/backing-dev.h>
 #include <linux/buffer_head.h>
 #include "internal.h"
 
+#define inode_to_bdi(inode)	((inode)->i_mapping->backing_dev_info)
 
-/**
- * writeback_acquire - attempt to get exclusive writeback access to a device
- * @bdi: the device's backing_dev_info structure
- *
- * It is a waste of resources to have more than one pdflush thread blocked on
- * a single request queue.  Exclusion at the request_queue level is obtained
- * via a flag in the request_queue's backing_dev_info.state.
- *
- * Non-request_queue-backed address_spaces will share default_backing_dev_info,
- * unless they implement their own.  Which is somewhat inefficient, as this
- * may prevent concurrent writeback against multiple devices.
+/*
+ * We don't actually have pdflush, but this one is exported though /proc...
+ */
+int nr_pdflush_threads;
+
+static void generic_sync_wb_inodes(struct bdi_writeback *wb,
+				   struct super_block *sb,
+				   struct writeback_control *wbc);
+
+/*
+ * Work items for the bdi_writeback threads
  */
-static int writeback_acquire(struct backing_dev_info *bdi)
+struct bdi_work {
+	struct list_head list;
+	struct list_head wait_list;
+	struct rcu_head rcu_head;
+
+	unsigned long seen;
+	atomic_t pending;
+
+	unsigned long sb_data;
+	unsigned long nr_pages;
+	enum writeback_sync_modes sync_mode;
+
+	unsigned long state;
+};
+
+static struct super_block *bdi_work_sb(struct bdi_work *work)
+{
+	return (struct super_block *) (work->sb_data & ~1UL);
+}
+
+static inline bool bdi_work_on_stack(struct bdi_work *work)
 {
-	return !test_and_set_bit(BDI_pdflush, &bdi->state);
+	return work->sb_data & 1UL;
+}
+
+static inline void bdi_work_init(struct bdi_work *work, struct super_block *sb,
+				 unsigned long nr_pages,
+				 enum writeback_sync_modes sync_mode)
+{
+	INIT_RCU_HEAD(&work->rcu_head);
+	work->sb_data = (unsigned long) sb;
+	work->nr_pages = nr_pages;
+	work->sync_mode = sync_mode;
+	work->state = 1;
+}
+
+static inline void bdi_work_init_on_stack(struct bdi_work *work,
+					  struct super_block *sb,
+					  unsigned long nr_pages,
+					  enum writeback_sync_modes sync_mode)
+{
+	bdi_work_init(work, sb, nr_pages, sync_mode);
+	work->sb_data |= 1UL;
 }
 
 /**
  * writeback_in_progress - determine whether there is writeback in progress
  * @bdi: the device's backing_dev_info structure.
  *
- * Determine whether there is writeback in progress against a backing device.
+ * Determine whether there is writeback waiting to be handled against a
+ * backing device.
  */
 int writeback_in_progress(struct backing_dev_info *bdi)
 {
-	return test_bit(BDI_pdflush, &bdi->state);
+	return !list_empty(&bdi->work_list);
 }
 
-/**
- * writeback_release - relinquish exclusive writeback access against a device.
- * @bdi: the device's backing_dev_info structure
+static void bdi_work_clear(struct bdi_work *work)
+{
+	clear_bit(0, &work->state);
+	smp_mb__after_clear_bit();
+	wake_up_bit(&work->state, 0);
+}
+
+static void bdi_work_free(struct rcu_head *head)
+{
+	struct bdi_work *work = container_of(head, struct bdi_work, rcu_head);
+
+	if (!bdi_work_on_stack(work))
+		kfree(work);
+	else
+		bdi_work_clear(work);
+}
+
+static void wb_work_complete(struct bdi_work *work)
+{
+	const enum writeback_sync_modes sync_mode = work->sync_mode;
+
+	/*
+	 * For allocated work, we can clear the done/seen bit right here.
+	 * For on-stack work, we need to postpone both the clear and free
+	 * to after the RCU grace period, since the stack could be invalidated
+	 * as soon as bdi_work_clear() has done the wakeup.
+	 */
+	if (!bdi_work_on_stack(work))
+		bdi_work_clear(work);
+	if (sync_mode == WB_SYNC_NONE || bdi_work_on_stack(work))
+		call_rcu(&work->rcu_head, bdi_work_free);
+}
+
+static void wb_clear_pending(struct bdi_writeback *wb, struct bdi_work *work)
+{
+	/*
+	 * The caller has retrieved the work arguments from this work,
+	 * drop our reference. If this is the last ref, delete and free it
+	 */
+	if (atomic_dec_and_test(&work->pending)) {
+		struct backing_dev_info *bdi = wb->bdi;
+
+		spin_lock(&bdi->wb_lock);
+		list_del_rcu(&work->list);
+		spin_unlock(&bdi->wb_lock);
+
+		wb_work_complete(work);
+	}
+}
+
+static void wb_start_writeback(struct bdi_writeback *wb, struct bdi_work *work)
+{
+	/*
+	 * If we failed allocating the bdi work item, wake up the wb thread
+	 * always. As a safety precaution, it'll flush out everything
+	 */
+	if (!wb_has_dirty_io(wb) && work)
+		wb_clear_pending(wb, work);
+	else if (wb->task)
+		wake_up_process(wb->task);
+}
+
+static void bdi_queue_work(struct backing_dev_info *bdi, struct bdi_work *work)
+{
+	if (work) {
+		work->seen = bdi->wb_mask;
+		BUG_ON(!work->seen);
+		atomic_set(&work->pending, bdi->wb_cnt);
+		BUG_ON(!bdi->wb_cnt);
+
+		/*
+		 * Make sure stores are seen before it appears on the list
+		 */
+		smp_mb();
+
+		spin_lock(&bdi->wb_lock);
+		list_add_tail_rcu(&work->list, &bdi->work_list);
+		spin_unlock(&bdi->wb_lock);
+	}
+}
+
+static void bdi_sched_work(struct backing_dev_info *bdi, struct bdi_work *work)
+{
+	if (!bdi_wblist_needs_lock(bdi))
+		wb_start_writeback(&bdi->wb, work);
+	else {
+		struct bdi_writeback *wb;
+		int idx;
+
+		idx = srcu_read_lock(&bdi->srcu);
+
+		list_for_each_entry_rcu(wb, &bdi->wb_list, list)
+			wb_start_writeback(wb, work);
+
+		srcu_read_unlock(&bdi->srcu, idx);
+	}
+}
+
+static void __bdi_start_work(struct backing_dev_info *bdi,
+			     struct bdi_work *work)
+{
+	/*
+	 * If the default thread isn't there, make sure we add it. When
+	 * it gets created and wakes up, we'll run this work.
+	 */
+	if (unlikely(list_empty_careful(&bdi->wb_list)))
+		bdi_add_default_flusher_task(bdi);
+	else
+		bdi_sched_work(bdi, work);
+}
+
+static void bdi_start_work(struct backing_dev_info *bdi, struct bdi_work *work)
+{
+	/*
+	 * If the default thread isn't there, make sure we add it. When
+	 * it gets created and wakes up, we'll run this work.
+	 */
+	if (unlikely(list_empty_careful(&bdi->wb_list))) {
+		spin_lock(&bdi_lock);
+		bdi_add_default_flusher_task(bdi);
+		spin_unlock(&bdi_lock);
+	} else
+		bdi_sched_work(bdi, work);
+}
+
+/*
+ * Used for on-stack allocated work items. The caller needs to wait until
+ * the wb threads have acked the work before it's safe to continue.
+ */
+static void bdi_wait_on_work_clear(struct bdi_work *work)
+{
+	wait_on_bit(&work->state, 0, bdi_sched_wait, TASK_UNINTERRUPTIBLE);
+}
+
+static struct bdi_work *bdi_alloc_work(struct super_block *sb, long nr_pages,
+				       enum writeback_sync_modes sync_mode)
+{
+	struct bdi_work *work;
+
+	work = kmalloc(sizeof(*work), GFP_ATOMIC);
+	if (work)
+		bdi_work_init(work, sb, nr_pages, sync_mode);
+
+	return work;
+}
+
+void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
+			 long nr_pages, enum writeback_sync_modes sync_mode)
+{
+	const bool must_wait = sync_mode == WB_SYNC_ALL;
+	struct bdi_work work_stack, *work = NULL;
+
+	if (!must_wait)
+		work = bdi_alloc_work(sb, nr_pages, sync_mode);
+
+	if (!work) {
+		work = &work_stack;
+		bdi_work_init_on_stack(work, sb, nr_pages, sync_mode);
+	}
+
+	bdi_queue_work(bdi, work);
+	bdi_start_work(bdi, work);
+
+	/*
+	 * If the sync mode is WB_SYNC_ALL, block waiting for the work to
+	 * complete. If not, we only need to wait for the work to be started,
+	 * if we allocated it on-stack. We use the same mechanism, if the
+	 * wait bit is set in the bdi_work struct, then threads will not
+	 * clear pending until after they are done.
+	 *
+	 * Note that work == &work_stack if must_wait is true, so we don't
+	 * need to do call_rcu() here ever, since the completion path will
+	 * have done that for us.
+	 */
+	if (must_wait || work == &work_stack) {
+		bdi_wait_on_work_clear(work);
+		if (work != &work_stack)
+			call_rcu(&work->rcu_head, bdi_work_free);
+	}
+}
+
+/*
+ * The maximum number of pages to writeout in a single bdi flush/kupdate
+ * operation.  We do this so we don't hold I_SYNC 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
+
+/*
+ * 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_interval.  But if a writeback event
+ * takes longer than a dirty_writeback_interval 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 long wb_kupdated(struct bdi_writeback *wb)
+{
+	unsigned long oldest_jif;
+	long nr_to_write, wrote = 0;
+	struct writeback_control wbc = {
+		.bdi			= wb->bdi,
+		.sync_mode		= WB_SYNC_NONE,
+		.older_than_this	= &oldest_jif,
+		.nr_to_write		= 0,
+		.for_kupdate		= 1,
+		.range_cyclic		= 1,
+	};
+
+	oldest_jif = jiffies - msecs_to_jiffies(dirty_expire_interval * 10);
+
+	nr_to_write = global_page_state(NR_FILE_DIRTY) +
+			global_page_state(NR_UNSTABLE_NFS) +
+			(inodes_stat.nr_inodes - inodes_stat.nr_unused);
+
+	while (nr_to_write > 0) {
+		wbc.more_io = 0;
+		wbc.encountered_congestion = 0;
+		wbc.nr_to_write = MAX_WRITEBACK_PAGES;
+		generic_sync_wb_inodes(wb, NULL, &wbc);
+		wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write;
+		if (wbc.nr_to_write > 0)
+			break;	/* All the old data is written */
+		nr_to_write -= MAX_WRITEBACK_PAGES;
+	}
+
+	return wrote;
+}
+
+static inline bool over_bground_thresh(void)
+{
+	unsigned long background_thresh, dirty_thresh;
+
+	get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
+
+	return (global_page_state(NR_FILE_DIRTY) +
+		global_page_state(NR_UNSTABLE_NFS) >= background_thresh);
+}
+
+static long __wb_writeback(struct bdi_writeback *wb, long nr_pages,
+			   struct super_block *sb,
+			   enum writeback_sync_modes sync_mode)
+{
+	struct writeback_control wbc = {
+		.bdi			= wb->bdi,
+		.sync_mode		= sync_mode,
+		.older_than_this	= NULL,
+		.range_cyclic		= 1,
+	};
+	long wrote = 0;
+
+	for (;;) {
+		if (sync_mode == WB_SYNC_NONE && nr_pages <= 0 &&
+		    !over_bground_thresh())
+			break;
+
+		wbc.more_io = 0;
+		wbc.encountered_congestion = 0;
+		wbc.nr_to_write = MAX_WRITEBACK_PAGES;
+		wbc.pages_skipped = 0;
+		generic_sync_wb_inodes(wb, sb, &wbc);
+		nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
+		wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write;
+		/*
+		 * If we ran out of stuff to write, bail unless more_io got set
+		 */
+		if (wbc.nr_to_write > 0 || wbc.pages_skipped > 0) {
+			if (wbc.more_io)
+				continue;
+			break;
+		}
+	}
+
+	return wrote;
+}
+
+/*
+ * Return the next bdi_work struct that hasn't been processed by this
+ * wb thread yet
+ */
+static struct bdi_work *get_next_work_item(struct backing_dev_info *bdi,
+					   struct bdi_writeback *wb)
+{
+	struct bdi_work *work, *ret = NULL;
+
+	rcu_read_lock();
+
+	list_for_each_entry_rcu(work, &bdi->work_list, list) {
+		if (!test_and_clear_bit(wb->nr, &work->seen))
+			continue;
+
+		ret = work;
+		break;
+	}
+
+	rcu_read_unlock();
+	return ret;
+}
+
+/*
+ * Retrieve work items and do the writeback they describe
+ */
+static long wb_writeback(struct bdi_writeback *wb)
+{
+	struct backing_dev_info *bdi = wb->bdi;
+	struct bdi_work *work;
+	long wrote = 0;
+
+	while ((work = get_next_work_item(bdi, wb)) != NULL) {
+		struct super_block *sb = bdi_work_sb(work);
+		long nr_pages = work->nr_pages;
+		enum writeback_sync_modes sync_mode = work->sync_mode;
+
+		/*
+		 * If this isn't a data integrity operation, just notify
+		 * that we have seen this work and we are now starting it.
+		 */
+		if (sync_mode == WB_SYNC_NONE)
+			wb_clear_pending(wb, work);
+
+		wrote += __wb_writeback(wb, nr_pages, sb, sync_mode);
+
+		/*
+		 * This is a data integrity writeback, so only do the
+		 * notification when we have completed the work.
+		 */
+		if (sync_mode == WB_SYNC_ALL)
+			wb_clear_pending(wb, work);
+	}
+
+	return wrote;
+}
+
+/*
+ * This will be inlined in bdi_writeback_task() once we get rid of any
+ * dirty inodes on the default_backing_dev_info
+ */
+long wb_do_writeback(struct bdi_writeback *wb)
+{
+	long wrote;
+
+	/*
+	 * We get here in two cases:
+	 *
+	 *  schedule_timeout() returned because the dirty writeback
+	 *  interval has elapsed. If that happens, the work item list
+	 *  will be empty and we will proceed to do kupdated style writeout.
+	 *
+	 *  Someone called bdi_start_writeback(), which put one/more work
+	 *  items on the work_list. Process those.
+	 */
+	if (list_empty(&wb->bdi->work_list))
+		wrote = wb_kupdated(wb);
+	else
+		wrote = wb_writeback(wb);
+
+	return wrote;
+}
+
+/*
+ * Handle writeback of dirty data for the device backed by this bdi. Also
+ * wakes up periodically and does kupdated style flushing.
+ */
+int bdi_writeback_task(struct bdi_writeback *wb)
+{
+	unsigned long last_active = jiffies;
+	unsigned long wait_jiffies = -1UL;
+	long pages_written;
+
+	while (!kthread_should_stop()) {
+		pages_written = wb_do_writeback(wb);
+
+		if (pages_written)
+			last_active = jiffies;
+		else if (wait_jiffies != -1UL) {
+			unsigned long max_idle;
+
+			/*
+			 * Longest period of inactivity that we tolerate. If we
+			 * see dirty data again later, the task will get
+			 * recreated automatically.
+			 */
+			max_idle = max(5UL * 60 * HZ, wait_jiffies);
+			if (time_after(jiffies, max_idle + last_active) &&
+			    wb_is_default_task(wb))
+				break;
+		}
+
+		wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10);
+		set_current_state(TASK_INTERRUPTIBLE);
+		schedule_timeout(wait_jiffies);
+		try_to_freeze();
+	}
+
+	return 0;
+}
+
+/*
+ * Schedule writeback for all backing devices. Expensive! If this is a data
+ * integrity operation, writeback will be complete when this returns. If
+ * we are simply called for WB_SYNC_NONE, then writeback will merely be
+ * scheduled to run.
+ */
+void bdi_writeback_all(struct super_block *sb, struct writeback_control *wbc)
+{
+	const bool must_wait = wbc->sync_mode == WB_SYNC_ALL;
+	struct backing_dev_info *bdi, *tmp;
+	struct bdi_work *work;
+	LIST_HEAD(list);
+
+	/*
+	 * If this isn't a data integrity writeback, just drop it if
+	 * someone is already holding the bdi_lock
+	 */
+	if (!spin_trylock(&bdi_lock)) {
+		if (!must_wait)
+			return;
+		spin_lock(&bdi_lock);
+	}
+
+restart:
+	list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
+		struct bdi_work *work;
+
+		if (!bdi_has_dirty_io(bdi))
+			continue;
+
+		/*
+		 * If work allocation fails, do the writes inline. An
+		 * alternative approach would be too fall back to an on-stack
+		 * allocation of work. For that we need to drop the bdi_lock
+		 * and restart the scan afterwards, though.
+		 */
+		work = bdi_alloc_work(sb, wbc->nr_to_write, wbc->sync_mode);
+		if (!work) {
+			if (!must_wait)
+				continue;
+
+			spin_unlock(&bdi_lock);
+			wbc->bdi = bdi;
+			generic_sync_bdi_inodes(sb, wbc);
+			spin_lock(&bdi_lock);
+			goto restart;
+		}
+		if (must_wait)
+			list_add_tail(&work->wait_list, &list);
+
+		bdi_queue_work(bdi, work);
+		__bdi_start_work(bdi, work);
+	}
+
+	spin_unlock(&bdi_lock);
+
+	/*
+	 * If this is for WB_SYNC_ALL, wait for pending work to complete
+	 * before returning.
+	 */
+	while (!list_empty(&list)) {
+		work = list_entry(list.next, struct bdi_work, wait_list);
+		list_del(&work->wait_list);
+		bdi_wait_on_work_clear(work);
+		call_rcu(&work->rcu_head, bdi_work_free);
+	}
+}
+
+/*
+ * If the filesystem didn't provide a way to map an inode to a dedicated
+ * flusher thread, it doesn't support more than 1 thread. So we know it's
+ * the default thread, return that.
  */
-static void writeback_release(struct backing_dev_info *bdi)
+static inline struct bdi_writeback *inode_get_wb(struct inode *inode)
 {
-	BUG_ON(!writeback_in_progress(bdi));
-	clear_bit(BDI_pdflush, &bdi->state);
+	const struct super_operations *sop = inode->i_sb->s_op;
+
+	if (!sop->inode_get_wb)
+		return &inode_to_bdi(inode)->wb;
+
+	return sop->inode_get_wb(inode);
 }
 
 /**
@@ -158,12 +681,21 @@ void __mark_inode_dirty(struct inode *in
 			goto out;
 
 		/*
-		 * If the inode was already on s_dirty/s_io/s_more_io, don't
-		 * reposition it (that would break s_dirty time-ordering).
+		 * If the inode was already on b_dirty/b_io/b_more_io, don't
+		 * reposition it (that would break b_dirty time-ordering).
 		 */
 		if (!was_dirty) {
+			struct bdi_writeback *wb = inode_get_wb(inode);
+			struct backing_dev_info *bdi = wb->bdi;
+
+			if (bdi_cap_writeback_dirty(bdi) &&
+			    !test_bit(BDI_registered, &bdi->state)) {
+				WARN_ON(1);
+				printk("bdi-%s not registered\n", bdi->name);
+			}
+
 			inode->dirtied_when = jiffies;
-			list_move(&inode->i_list, &sb->s_dirty);
+			list_move(&inode->i_list, &wb->b_dirty);
 		}
 	}
 out:
@@ -184,31 +716,32 @@ static int write_inode(struct inode *ino
  * furthest end of its superblock's dirty-inode list.
  *
  * Before stamping the inode's ->dirtied_when, we check to see whether it is
- * already the most-recently-dirtied inode on the s_dirty list.  If that is
+ * already the most-recently-dirtied inode on the b_dirty list.  If that is
  * the case then the inode must have been redirtied while it was being written
  * out and we don't reset its dirtied_when.
  */
 static void redirty_tail(struct inode *inode)
 {
-	struct super_block *sb = inode->i_sb;
+	struct bdi_writeback *wb = inode_get_wb(inode);
 
-	if (!list_empty(&sb->s_dirty)) {
-		struct inode *tail_inode;
+	if (!list_empty(&wb->b_dirty)) {
+		struct inode *tail;
 
-		tail_inode = list_entry(sb->s_dirty.next, struct inode, i_list);
-		if (time_before(inode->dirtied_when,
-				tail_inode->dirtied_when))
+		tail = list_entry(wb->b_dirty.next, struct inode, i_list);
+		if (time_before(inode->dirtied_when, tail->dirtied_when))
 			inode->dirtied_when = jiffies;
 	}
-	list_move(&inode->i_list, &sb->s_dirty);
+	list_move(&inode->i_list, &wb->b_dirty);
 }
 
 /*
- * requeue inode for re-scanning after sb->s_io list is exhausted.
+ * requeue inode for re-scanning after bdi->b_io list is exhausted.
  */
 static void requeue_io(struct inode *inode)
 {
-	list_move(&inode->i_list, &inode->i_sb->s_more_io);
+	struct bdi_writeback *wb = inode_get_wb(inode);
+
+	list_move(&inode->i_list, &wb->b_more_io);
 }
 
 static void inode_sync_complete(struct inode *inode)
@@ -255,20 +788,11 @@ static void move_expired_inodes(struct l
 /*
  * Queue all expired dirty inodes for io, eldest first.
  */
-static void queue_io(struct super_block *sb,
-				unsigned long *older_than_this)
-{
-	list_splice_init(&sb->s_more_io, sb->s_io.prev);
-	move_expired_inodes(&sb->s_dirty, &sb->s_io, older_than_this);
-}
-
-int sb_has_dirty_inodes(struct super_block *sb)
+static void queue_io(struct bdi_writeback *wb, unsigned long *older_than_this)
 {
-	return !list_empty(&sb->s_dirty) ||
-	       !list_empty(&sb->s_io) ||
-	       !list_empty(&sb->s_more_io);
+	list_splice_init(&wb->b_more_io, wb->b_io.prev);
+	move_expired_inodes(&wb->b_dirty, &wb->b_io, older_than_this);
 }
-EXPORT_SYMBOL(sb_has_dirty_inodes);
 
 /*
  * Write a single inode's dirty pages and inode data out to disk.
@@ -322,11 +846,11 @@ __sync_single_inode(struct inode *inode,
 			/*
 			 * We didn't write back all the pages.  nfs_writepages()
 			 * sometimes bales out without doing anything. Redirty
-			 * the inode; Move it from s_io onto s_more_io/s_dirty.
+			 * the inode; Move it from b_io onto b_more_io/b_dirty.
 			 */
 			/*
 			 * akpm: if the caller was the kupdate function we put
-			 * this inode at the head of s_dirty so it gets first
+			 * this inode at the head of b_dirty so it gets first
 			 * consideration.  Otherwise, move it to the tail, for
 			 * the reasons described there.  I'm not really sure
 			 * how much sense this makes.  Presumably I had a good
@@ -336,7 +860,7 @@ __sync_single_inode(struct inode *inode,
 			if (wbc->for_kupdate) {
 				/*
 				 * For the kupdate function we move the inode
-				 * to s_more_io so it will get more writeout as
+				 * to b_more_io so it will get more writeout as
 				 * soon as the queue becomes uncongested.
 				 */
 				inode->i_state |= I_DIRTY_PAGES;
@@ -402,10 +926,10 @@ __writeback_single_inode(struct inode *i
 	if ((wbc->sync_mode != WB_SYNC_ALL) && (inode->i_state & I_SYNC)) {
 		/*
 		 * We're skipping this inode because it's locked, and we're not
-		 * doing writeback-for-data-integrity.  Move it to s_more_io so
-		 * that writeback can proceed with the other inodes on s_io.
+		 * doing writeback-for-data-integrity.  Move it to b_more_io so
+		 * that writeback can proceed with the other inodes on b_io.
 		 * We'll have another go at writing back this inode when we
-		 * completed a full scan of s_io.
+		 * completed a full scan of b_io.
 		 */
 		requeue_io(inode);
 		return 0;
@@ -428,51 +952,34 @@ __writeback_single_inode(struct inode *i
 	return __sync_single_inode(inode, wbc);
 }
 
-/*
- * Write out a superblock's list of dirty inodes.  A wait will be performed
- * upon no inodes, all inodes or the final one, depending upon sync_mode.
- *
- * If older_than_this is non-NULL, then only write out inodes which
- * had their first dirtying at a time earlier than *older_than_this.
- *
- * If we're a pdflush thread, then implement pdflush collision avoidance
- * against the entire list.
- *
- * If `bdi' is non-zero then we're being asked to writeback a specific queue.
- * This function assumes that the blockdev superblock's inodes are backed by
- * a variety of queues, so all inodes are searched.  For other superblocks,
- * assume that all inodes are backed by the same queue.
- *
- * FIXME: this linear search could get expensive with many fileystems.  But
- * how to fix?  We need to go from an address_space to all inodes which share
- * a queue with that address_space.  (Easy: have a global "dirty superblocks"
- * list).
- *
- * The inodes to be written are parked on sb->s_io.  They are moved back onto
- * sb->s_dirty as they are selected for writing.  This way, none can be missed
- * on the writer throttling path, and we get decent balancing between many
- * throttled threads: we don't want them all piling up on inode_sync_wait.
- */
-void generic_sync_sb_inodes(struct super_block *sb,
-				struct writeback_control *wbc)
+static void generic_sync_wb_inodes(struct bdi_writeback *wb,
+				   struct super_block *sb,
+				   struct writeback_control *wbc)
 {
+	const int is_blkdev_sb = sb_is_blkdev_sb(sb);
 	const unsigned long start = jiffies;	/* livelock avoidance */
-	int sync = wbc->sync_mode == WB_SYNC_ALL;
 
 	spin_lock(&inode_lock);
-	if (!wbc->for_kupdate || list_empty(&sb->s_io))
-		queue_io(sb, wbc->older_than_this);
 
-	while (!list_empty(&sb->s_io)) {
-		struct inode *inode = list_entry(sb->s_io.prev,
+	if (!wbc->for_kupdate || list_empty(&wb->b_io))
+		queue_io(wb, wbc->older_than_this);
+
+	while (!list_empty(&wb->b_io)) {
+		struct inode *inode = list_entry(wb->b_io.prev,
 						struct inode, i_list);
-		struct address_space *mapping = inode->i_mapping;
-		struct backing_dev_info *bdi = mapping->backing_dev_info;
 		long pages_skipped;
 
-		if (!bdi_cap_writeback_dirty(bdi)) {
+		/*
+		 * super block given and doesn't match, skip this inode
+		 */
+		if (sb && sb != inode->i_sb) {
+			redirty_tail(inode);
+			continue;
+		}
+
+		if (!bdi_cap_writeback_dirty(wb->bdi)) {
 			redirty_tail(inode);
-			if (sb_is_blkdev_sb(sb)) {
+			if (is_blkdev_sb) {
 				/*
 				 * Dirty memory-backed blockdev: the ramdisk
 				 * driver does this.  Skip just this inode
@@ -492,21 +999,14 @@ void generic_sync_sb_inodes(struct super
 			continue;
 		}
 
-		if (wbc->nonblocking && bdi_write_congested(bdi)) {
+		if (wbc->nonblocking && bdi_write_congested(wb->bdi)) {
 			wbc->encountered_congestion = 1;
-			if (!sb_is_blkdev_sb(sb))
+			if (!is_blkdev_sb)
 				break;		/* Skip a congested fs */
 			requeue_io(inode);
 			continue;		/* Skip a congested blockdev */
 		}
 
-		if (wbc->bdi && bdi != wbc->bdi) {
-			if (!sb_is_blkdev_sb(sb))
-				break;		/* fs has the wrong queue */
-			requeue_io(inode);
-			continue;		/* blockdev has wrong queue */
-		}
-
 		/*
 		 * Was this inode dirtied after sync_sb_inodes was called?
 		 * This keeps sync from extra jobs and livelock.
@@ -514,16 +1014,10 @@ void generic_sync_sb_inodes(struct super
 		if (inode_dirtied_after(inode, start))
 			break;
 
-		/* Is another pdflush already flushing this queue? */
-		if (current_is_pdflush() && !writeback_acquire(bdi))
-			break;
-
 		BUG_ON(inode->i_state & I_FREEING);
 		__iget(inode);
 		pages_skipped = wbc->pages_skipped;
 		__writeback_single_inode(inode, wbc);
-		if (current_is_pdflush())
-			writeback_release(bdi);
 		if (wbc->pages_skipped != pages_skipped) {
 			/*
 			 * writeback is not making progress due to locked
@@ -539,13 +1033,71 @@ void generic_sync_sb_inodes(struct super
 			wbc->more_io = 1;
 			break;
 		}
-		if (!list_empty(&sb->s_more_io))
+		if (!list_empty(&wb->b_more_io))
 			wbc->more_io = 1;
 	}
 
-	if (sync) {
+	spin_unlock(&inode_lock);
+	/* Leave any unwritten inodes on b_io */
+}
+
+void generic_sync_bdi_inodes(struct super_block *sb,
+			     struct writeback_control *wbc)
+{
+	struct backing_dev_info *bdi = wbc->bdi;
+	struct bdi_writeback *wb;
+
+	/*
+	 * Common case is just a single wb thread and that is embedded in
+	 * the bdi, so it doesn't need locking
+	 */
+	if (!bdi_wblist_needs_lock(bdi))
+		generic_sync_wb_inodes(&bdi->wb, sb, wbc);
+	else {
+		int idx;
+
+		idx = srcu_read_lock(&bdi->srcu);
+
+		list_for_each_entry_rcu(wb, &bdi->wb_list, list)
+			generic_sync_wb_inodes(wb, sb, wbc);
+
+		srcu_read_unlock(&bdi->srcu, idx);
+	}
+}
+
+/*
+ * Write out a superblock's list of dirty inodes.  A wait will be performed
+ * upon no inodes, all inodes or the final one, depending upon sync_mode.
+ *
+ * If older_than_this is non-NULL, then only write out inodes which
+ * had their first dirtying at a time earlier than *older_than_this.
+ *
+ * If we're a pdlfush thread, then implement pdflush collision avoidance
+ * against the entire list.
+ *
+ * If `bdi' is non-zero then we're being asked to writeback a specific queue.
+ * This function assumes that the blockdev superblock's inodes are backed by
+ * a variety of queues, so all inodes are searched.  For other superblocks,
+ * assume that all inodes are backed by the same queue.
+ *
+ * The inodes to be written are parked on bdi->b_io.  They are moved back onto
+ * bdi->b_dirty as they are selected for writing.  This way, none can be missed
+ * on the writer throttling path, and we get decent balancing between many
+ * throttled threads: we don't want them all piling up on inode_sync_wait.
+ */
+void generic_sync_sb_inodes(struct super_block *sb,
+				struct writeback_control *wbc)
+{
+	if (wbc->bdi)
+		bdi_start_writeback(wbc->bdi, sb, wbc->nr_to_write, wbc->sync_mode);
+	else
+		bdi_writeback_all(sb, wbc);
+
+	if (wbc->sync_mode == WB_SYNC_ALL) {
 		struct inode *inode, *old_inode = NULL;
 
+		spin_lock(&inode_lock);
+
 		/*
 		 * Data integrity sync. Must wait for all pages under writeback,
 		 * because there may have been pages dirtied before our sync
@@ -583,10 +1135,8 @@ void generic_sync_sb_inodes(struct super
 		}
 		spin_unlock(&inode_lock);
 		iput(old_inode);
-	} else
-		spin_unlock(&inode_lock);
+	}
 
-	return;		/* Leave any unwritten inodes on s_io */
 }
 EXPORT_SYMBOL_GPL(generic_sync_sb_inodes);
 
@@ -597,58 +1147,6 @@ static void sync_sb_inodes(struct super_
 }
 
 /*
- * Start writeback of dirty pagecache data against all unlocked inodes.
- *
- * Note:
- * We don't need to grab a reference to superblock here. If it has non-empty
- * ->s_dirty it's hadn't been killed yet and kill_super() won't proceed
- * past sync_inodes_sb() until the ->s_dirty/s_io/s_more_io lists are all
- * empty. Since __sync_single_inode() regains inode_lock before it finally moves
- * inode from superblock lists we are OK.
- *
- * If `older_than_this' is non-zero then only flush inodes which have a
- * flushtime older than *older_than_this.
- *
- * If `bdi' is non-zero then we will scan the first inode against each
- * superblock until we find the matching ones.  One group will be the dirty
- * inodes against a filesystem.  Then when we hit the dummy blockdev superblock,
- * sync_sb_inodes will seekout the blockdev which matches `bdi'.  Maybe not
- * super-efficient but we're about to do a ton of I/O...
- */
-void
-writeback_inodes(struct writeback_control *wbc)
-{
-	struct super_block *sb;
-
-	might_sleep();
-	spin_lock(&sb_lock);
-restart:
-	list_for_each_entry_reverse(sb, &super_blocks, s_list) {
-		if (sb_has_dirty_inodes(sb)) {
-			/* we're making our own get_super here */
-			sb->s_count++;
-			spin_unlock(&sb_lock);
-			/*
-			 * If we can't get the readlock, there's no sense in
-			 * waiting around, most of the time the FS is going to
-			 * be unmounted by the time it is released.
-			 */
-			if (down_read_trylock(&sb->s_umount)) {
-				if (sb->s_root)
-					sync_sb_inodes(sb, wbc);
-				up_read(&sb->s_umount);
-			}
-			spin_lock(&sb_lock);
-			if (__put_super_and_need_restart(sb))
-				goto restart;
-		}
-		if (wbc->nr_to_write <= 0)
-			break;
-	}
-	spin_unlock(&sb_lock);
-}
-
-/*
  * writeback and wait upon the filesystem's dirty inodes.  The caller will
  * do this in two passes - one to write, and one to wait.
  *
diff -Nraup linux-2.6.30/fs/fuse/inode.c linux-2.6.30_bdiflusherv10/fs/fuse/inode.c
--- linux-2.6.30/fs/fuse/inode.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/fs/fuse/inode.c	2009-06-15 15:52:50.000000000 +0800
@@ -484,6 +484,7 @@ int fuse_conn_init(struct fuse_conn *fc,
 	INIT_LIST_HEAD(&fc->bg_queue);
 	INIT_LIST_HEAD(&fc->entry);
 	atomic_set(&fc->num_waiting, 0);
+	fc->bdi.name = "fuse";
 	fc->bdi.ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
 	fc->bdi.unplug_io_fn = default_unplug_io_fn;
 	/* fuse does it's own writeback accounting */
diff -Nraup linux-2.6.30/fs/hugetlbfs/inode.c linux-2.6.30_bdiflusherv10/fs/hugetlbfs/inode.c
--- linux-2.6.30/fs/hugetlbfs/inode.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/fs/hugetlbfs/inode.c	2009-06-15 15:52:50.000000000 +0800
@@ -43,6 +43,7 @@ static const struct inode_operations hug
 static const struct inode_operations hugetlbfs_inode_operations;
 
 static struct backing_dev_info hugetlbfs_backing_dev_info = {
+	.name		= "hugetlbfs",
 	.ra_pages	= 0,	/* No readahead */
 	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,
 };
diff -Nraup linux-2.6.30/fs/nfs/client.c linux-2.6.30_bdiflusherv10/fs/nfs/client.c
--- linux-2.6.30/fs/nfs/client.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/fs/nfs/client.c	2009-06-15 15:52:50.000000000 +0800
@@ -836,6 +836,7 @@ static void nfs_server_set_fsinfo(struct
 		server->rsize = NFS_MAX_FILE_IO_SIZE;
 	server->rpages = (server->rsize + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
 
+	server->backing_dev_info.name = "nfs";
 	server->backing_dev_info.ra_pages = server->rpages * NFS_MAX_READAHEAD;
 
 	if (server->wsize > max_rpc_payload)
diff -Nraup linux-2.6.30/fs/ocfs2/dlm/dlmfs.c linux-2.6.30_bdiflusherv10/fs/ocfs2/dlm/dlmfs.c
--- linux-2.6.30/fs/ocfs2/dlm/dlmfs.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/fs/ocfs2/dlm/dlmfs.c	2009-06-15 15:52:50.000000000 +0800
@@ -325,6 +325,7 @@ clear_fields:
 }
 
 static struct backing_dev_info dlmfs_backing_dev_info = {
+	.name		= "ocfs2-dlmfs",
 	.ra_pages	= 0,	/* No readahead */
 	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,
 };
diff -Nraup linux-2.6.30/fs/ramfs/inode.c linux-2.6.30_bdiflusherv10/fs/ramfs/inode.c
--- linux-2.6.30/fs/ramfs/inode.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/fs/ramfs/inode.c	2009-06-15 15:52:50.000000000 +0800
@@ -46,6 +46,7 @@ static const struct super_operations ram
 static const struct inode_operations ramfs_dir_inode_operations;
 
 static struct backing_dev_info ramfs_backing_dev_info = {
+	.name		= "ramfs",
 	.ra_pages	= 0,	/* No readahead */
 	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK |
 			  BDI_CAP_MAP_DIRECT | BDI_CAP_MAP_COPY |
diff -Nraup linux-2.6.30/fs/super.c linux-2.6.30_bdiflusherv10/fs/super.c
--- linux-2.6.30/fs/super.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/fs/super.c	2009-06-15 15:52:50.000000000 +0800
@@ -64,9 +64,6 @@ static struct super_block *alloc_super(s
 			s = NULL;
 			goto out;
 		}
-		INIT_LIST_HEAD(&s->s_dirty);
-		INIT_LIST_HEAD(&s->s_io);
-		INIT_LIST_HEAD(&s->s_more_io);
 		INIT_LIST_HEAD(&s->s_files);
 		INIT_LIST_HEAD(&s->s_instances);
 		INIT_HLIST_HEAD(&s->s_anon);
diff -Nraup linux-2.6.30/fs/sync.c linux-2.6.30_bdiflusherv10/fs/sync.c
--- linux-2.6.30/fs/sync.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/fs/sync.c	2009-06-15 16:01:07.000000000 +0800
@@ -23,7 +23,7 @@
  */
 static void do_sync(unsigned long wait)
 {
-	wakeup_pdflush(0);
+	wakeup_flusher_threads(0);
 	sync_inodes(0);		/* All mappings, inodes and their blockdevs */
 	vfs_dq_sync(NULL);
 	sync_supers();		/* Write the superblocks */
diff -Nraup linux-2.6.30/fs/sysfs/inode.c linux-2.6.30_bdiflusherv10/fs/sysfs/inode.c
--- linux-2.6.30/fs/sysfs/inode.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/fs/sysfs/inode.c	2009-06-15 15:52:50.000000000 +0800
@@ -29,6 +29,7 @@ static const struct address_space_operat
 };
 
 static struct backing_dev_info sysfs_backing_dev_info = {
+	.name		= "sysfs",
 	.ra_pages	= 0,	/* No readahead */
 	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,
 };
diff -Nraup linux-2.6.30/fs/ubifs/super.c linux-2.6.30_bdiflusherv10/fs/ubifs/super.c
--- linux-2.6.30/fs/ubifs/super.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/fs/ubifs/super.c	2009-06-15 15:52:50.000000000 +0800
@@ -1923,11 +1923,15 @@ static int ubifs_fill_super(struct super
 	 *
 	 * Read-ahead will be disabled because @c->bdi.ra_pages is 0.
 	 */
+	c->bdi.name = "ubifs",
 	c->bdi.capabilities = BDI_CAP_MAP_COPY;
 	c->bdi.unplug_io_fn = default_unplug_io_fn;
 	err  = bdi_init(&c->bdi);
 	if (err)
 		goto out_close;
+	err = bdi_register(&c->bdi, NULL, "ubifs");
+	if (err)
+		goto out_bdi;
 
 	err = ubifs_parse_options(c, data, 0);
 	if (err)
diff -Nraup linux-2.6.30/include/linux/backing-dev.h linux-2.6.30_bdiflusherv10/include/linux/backing-dev.h
--- linux-2.6.30/include/linux/backing-dev.h	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/include/linux/backing-dev.h	2009-06-15 15:52:50.000000000 +0800
@@ -13,6 +13,9 @@
 #include <linux/proportions.h>
 #include <linux/kernel.h>
 #include <linux/fs.h>
+#include <linux/sched.h>
+#include <linux/srcu.h>
+#include <linux/writeback.h>
 #include <asm/atomic.h>
 
 struct page;
@@ -23,9 +26,12 @@ struct dentry;
  * Bits in backing_dev_info.state
  */
 enum bdi_state {
-	BDI_pdflush,		/* A pdflush thread is working this device */
+	BDI_pending,		/* On its way to being activated */
+	BDI_wb_alloc,		/* Default embedded wb allocated */
+	BDI_wblist_lock,	/* bdi->wb_list now needs locking */
 	BDI_async_congested,	/* The async (write) queue is getting full */
 	BDI_sync_congested,	/* The sync queue is getting full */
+	BDI_registered,		/* bdi_register() was done */
 	BDI_unused,		/* Available bits start here */
 };
 
@@ -39,7 +45,23 @@ enum bdi_stat_item {
 
 #define BDI_STAT_BATCH (8*(1+ilog2(nr_cpu_ids)))
 
+struct bdi_writeback {
+	struct list_head list;			/* hangs off the bdi */
+
+	struct backing_dev_info *bdi;		/* our parent bdi */
+	unsigned int nr;
+
+	struct task_struct	*task;		/* writeback task */
+	struct list_head	b_dirty;	/* dirty inodes */
+	struct list_head	b_io;		/* parked for writeback */
+	struct list_head	b_more_io;	/* parked for more writeback */
+};
+
+#define BDI_MAX_FLUSHERS	32
+
 struct backing_dev_info {
+	struct srcu_struct srcu; /* for wb_list read side protection */
+	struct list_head bdi_list;
 	unsigned long ra_pages;	/* max readahead in PAGE_CACHE_SIZE units */
 	unsigned long state;	/* Always use atomic bitops on this */
 	unsigned int capabilities; /* Device capabilities */
@@ -48,6 +70,8 @@ struct backing_dev_info {
 	void (*unplug_io_fn)(struct backing_dev_info *, struct page *);
 	void *unplug_io_data;
 
+	char *name;
+
 	struct percpu_counter bdi_stat[NR_BDI_STAT_ITEMS];
 
 	struct prop_local_percpu completions;
@@ -56,6 +80,14 @@ struct backing_dev_info {
 	unsigned int min_ratio;
 	unsigned int max_ratio, max_prop_frac;
 
+	struct bdi_writeback wb;  /* default writeback info for this bdi */
+	spinlock_t wb_lock;	  /* protects update side of wb_list */
+	struct list_head wb_list; /* the flusher threads hanging off this bdi */
+	unsigned long wb_mask;	  /* bitmask of registered tasks */
+	unsigned int wb_cnt;	  /* number of registered tasks */
+
+	struct list_head work_list;
+
 	struct device *dev;
 
 #ifdef CONFIG_DEBUG_FS
@@ -71,6 +103,33 @@ int bdi_register(struct backing_dev_info
 		const char *fmt, ...);
 int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev);
 void bdi_unregister(struct backing_dev_info *bdi);
+void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
+			 long nr_pages, enum writeback_sync_modes sync_mode);
+int bdi_writeback_task(struct bdi_writeback *wb);
+void bdi_writeback_all(struct super_block *sb, struct writeback_control *wbc);
+void bdi_add_default_flusher_task(struct backing_dev_info *bdi);
+void bdi_add_flusher_task(struct backing_dev_info *bdi);
+int bdi_has_dirty_io(struct backing_dev_info *bdi);
+
+extern spinlock_t bdi_lock;
+extern struct list_head bdi_list;
+
+static inline int wb_is_default_task(struct bdi_writeback *wb)
+{
+	return wb == &wb->bdi->wb;
+}
+
+static inline int bdi_wblist_needs_lock(struct backing_dev_info *bdi)
+{
+	return test_bit(BDI_wblist_lock, &bdi->state);
+}
+
+static inline int wb_has_dirty_io(struct bdi_writeback *wb)
+{
+	return !list_empty(&wb->b_dirty) ||
+	       !list_empty(&wb->b_io) ||
+	       !list_empty(&wb->b_more_io);
+}
 
 static inline void __add_bdi_stat(struct backing_dev_info *bdi,
 		enum bdi_stat_item item, s64 amount)
@@ -256,6 +315,11 @@ static inline bool bdi_cap_swap_backed(s
 	return bdi->capabilities & BDI_CAP_SWAP_BACKED;
 }
 
+static inline bool bdi_cap_flush_forker(struct backing_dev_info *bdi)
+{
+	return bdi == &default_backing_dev_info;
+}
+
 static inline bool mapping_cap_writeback_dirty(struct address_space *mapping)
 {
 	return bdi_cap_writeback_dirty(mapping->backing_dev_info);
@@ -271,4 +335,10 @@ static inline bool mapping_cap_swap_back
 	return bdi_cap_swap_backed(mapping->backing_dev_info);
 }
 
+static inline int bdi_sched_wait(void *word)
+{
+	schedule();
+	return 0;
+}
+
 #endif		/* _LINUX_BACKING_DEV_H */
diff -Nraup linux-2.6.30/include/linux/fs.h linux-2.6.30_bdiflusherv10/include/linux/fs.h
--- linux-2.6.30/include/linux/fs.h	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/include/linux/fs.h	2009-06-15 15:52:50.000000000 +0800
@@ -712,7 +712,7 @@ static inline int mapping_writably_mappe
 
 struct inode {
 	struct hlist_node	i_hash;
-	struct list_head	i_list;
+	struct list_head	i_list;		/* backing dev IO list */
 	struct list_head	i_sb_list;
 	struct list_head	i_dentry;
 	unsigned long		i_ino;
@@ -1329,9 +1329,6 @@ struct super_block {
 	struct xattr_handler	**s_xattr;
 
 	struct list_head	s_inodes;	/* all inodes */
-	struct list_head	s_dirty;	/* dirty inodes */
-	struct list_head	s_io;		/* parked for writeback */
-	struct list_head	s_more_io;	/* parked for more writeback */
 	struct hlist_head	s_anon;		/* anonymous dentries for (nfs) exporting */
 	struct list_head	s_files;
 	/* s_dentry_lru and s_nr_dentry_unused are protected by dcache_lock */
@@ -1553,11 +1550,14 @@ extern ssize_t vfs_readv(struct file *, 
 extern ssize_t vfs_writev(struct file *, const struct iovec __user *,
 		unsigned long, loff_t *);
 
+struct bdi_writeback;
+
 struct super_operations {
    	struct inode *(*alloc_inode)(struct super_block *sb);
 	void (*destroy_inode)(struct inode *);
 
    	void (*dirty_inode) (struct inode *);
+	struct bdi_writeback *(*inode_get_wb) (struct inode *);
 	int (*write_inode) (struct inode *, int);
 	void (*drop_inode) (struct inode *);
 	void (*delete_inode) (struct inode *);
@@ -2066,6 +2066,8 @@ extern int invalidate_inode_pages2_range
 					 pgoff_t start, pgoff_t end);
 extern void generic_sync_sb_inodes(struct super_block *sb,
 				struct writeback_control *wbc);
+extern void generic_sync_bdi_inodes(struct super_block *sb,
+				struct writeback_control *);
 extern int write_inode_now(struct inode *, int);
 extern int filemap_fdatawrite(struct address_space *);
 extern int filemap_flush(struct address_space *);
@@ -2183,7 +2185,6 @@ extern int bdev_read_only(struct block_d
 extern int set_blocksize(struct block_device *, int);
 extern int sb_set_blocksize(struct super_block *, int);
 extern int sb_min_blocksize(struct super_block *, int);
-extern int sb_has_dirty_inodes(struct super_block *);
 
 extern int generic_file_mmap(struct file *, struct vm_area_struct *);
 extern int generic_file_readonly_mmap(struct file *, struct vm_area_struct *);
diff -Nraup linux-2.6.30/include/linux/writeback.h linux-2.6.30_bdiflusherv10/include/linux/writeback.h
--- linux-2.6.30/include/linux/writeback.h	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/include/linux/writeback.h	2009-06-15 15:54:20.000000000 +0800
@@ -14,17 +14,6 @@ extern struct list_head inode_in_use;
 extern struct list_head inode_unused;
 
 /*
- * Yes, writeback.h requires sched.h
- * No, sched.h is not included from here.
- */
-static inline int task_is_pdflush(struct task_struct *task)
-{
-	return task->flags & PF_FLUSHER;
-}
-
-#define current_is_pdflush()	task_is_pdflush(current)
-
-/*
  * fs/fs-writeback.c
  */
 enum writeback_sync_modes {
@@ -79,6 +68,7 @@ struct writeback_control {
 void writeback_inodes(struct writeback_control *wbc);
 int inode_wait(void *);
 void sync_inodes_sb(struct super_block *, int wait);
+long wb_do_writeback(struct bdi_writeback *wb);
 void sync_inodes(int wait);
 
 /* writeback.h requires fs.h; it, too, is not included from here. */
@@ -99,7 +89,7 @@ static inline void inode_sync_wait(struc
 /*
  * mm/page-writeback.c
  */
-int wakeup_pdflush(long nr_pages);
+void wakeup_flusher_threads(long nr_pages);
 void laptop_io_completion(void);
 void laptop_sync_completion(void);
 void throttle_vm_writeout(gfp_t gfp_mask);
@@ -151,7 +141,6 @@ balance_dirty_pages_ratelimited(struct a
 typedef int (*writepage_t)(struct page *page, struct writeback_control *wbc,
 				void *data);
 
-int pdflush_operation(void (*fn)(unsigned long), unsigned long arg0);
 int generic_writepages(struct address_space *mapping,
 		       struct writeback_control *wbc);
 int write_cache_pages(struct address_space *mapping,
diff -Nraup linux-2.6.30/kernel/cgroup.c linux-2.6.30_bdiflusherv10/kernel/cgroup.c
--- linux-2.6.30/kernel/cgroup.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/kernel/cgroup.c	2009-06-15 15:52:50.000000000 +0800
@@ -598,6 +598,7 @@ static struct inode_operations cgroup_di
 static struct file_operations proc_cgroupstats_operations;
 
 static struct backing_dev_info cgroup_backing_dev_info = {
+	.name		= "cgroup",
 	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,
 };
 
diff -Nraup linux-2.6.30/mm/backing-dev.c linux-2.6.30_bdiflusherv10/mm/backing-dev.c
--- linux-2.6.30/mm/backing-dev.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/mm/backing-dev.c	2009-06-15 15:52:50.000000000 +0800
@@ -1,8 +1,11 @@
 
 #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>
@@ -14,6 +17,7 @@ void default_unplug_io_fn(struct backing
 EXPORT_SYMBOL(default_unplug_io_fn);
 
 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,
@@ -22,6 +26,16 @@ struct backing_dev_info default_backing_
 EXPORT_SYMBOL_GPL(default_backing_dev_info);
 
 static struct class *bdi_class;
+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);
+static void arm_supers_timer(void);
 
 #ifdef CONFIG_DEBUG_FS
 #include <linux/debugfs.h>
@@ -37,9 +51,29 @@ static void bdi_debug_init(void)
 static int bdi_debug_stats_show(struct seq_file *m, void *v)
 {
 	struct backing_dev_info *bdi = m->private;
+	struct bdi_writeback *wb;
 	unsigned long background_thresh;
 	unsigned long dirty_thresh;
 	unsigned long bdi_thresh;
+	unsigned long nr_dirty, nr_io, nr_more_io, nr_wb;
+	struct inode *inode;
+
+	/*
+	 * inode lock is enough here, the bdi->wb_list is protected by
+	 * RCU on the reader side
+	 */
+	nr_wb = nr_dirty = nr_io = nr_more_io = 0;
+	spin_lock(&inode_lock);
+	list_for_each_entry(wb, &bdi->wb_list, list) {
+		nr_wb++;
+		list_for_each_entry(inode, &wb->b_dirty, i_list)
+			nr_dirty++;
+		list_for_each_entry(inode, &wb->b_io, i_list)
+			nr_io++;
+		list_for_each_entry(inode, &wb->b_more_io, i_list)
+			nr_more_io++;
+	}
+	spin_unlock(&inode_lock);
 
 	get_dirty_limits(&background_thresh, &dirty_thresh, &bdi_thresh, bdi);
 
@@ -49,12 +83,22 @@ static int bdi_debug_stats_show(struct s
 		   "BdiReclaimable:   %8lu kB\n"
 		   "BdiDirtyThresh:   %8lu kB\n"
 		   "DirtyThresh:      %8lu kB\n"
-		   "BackgroundThresh: %8lu kB\n",
+		   "BackgroundThresh: %8lu kB\n"
+		   "WriteBack threads:%8lu\n"
+		   "b_dirty:          %8lu\n"
+		   "b_io:             %8lu\n"
+		   "b_more_io:        %8lu\n"
+		   "bdi_list:         %8u\n"
+		   "state:            %8lx\n"
+		   "wb_mask:          %8lx\n"
+		   "wb_list:          %8u\n"
+		   "wb_cnt:           %8u\n",
 		   (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));
+		   K(bdi_thresh), K(dirty_thresh),
+		   K(background_thresh), nr_wb, nr_dirty, nr_io, nr_more_io,
+		   !list_empty(&bdi->bdi_list), bdi->state, bdi->wb_mask,
+		   !list_empty(&bdi->wb_list), bdi->wb_cnt);
 #undef K
 
 	return 0;
@@ -185,6 +229,13 @@ static int __init default_bdi_init(void)
 {
 	int err;
 
+	sync_supers_tsk = kthread_run(bdi_sync_supers, NULL, "sync_supers");
+	BUG_ON(!sync_supers_tsk);
+
+	init_timer(&sync_supers_timer);
+	setup_timer(&sync_supers_timer, sync_supers_timer_fn, 0);
+	arm_supers_timer();
+
 	err = bdi_init(&default_backing_dev_info);
 	if (!err)
 		bdi_register(&default_backing_dev_info, NULL, "default");
@@ -193,6 +244,379 @@ static int __init default_bdi_init(void)
 }
 subsys_initcall(default_bdi_init);
 
+static int wb_assign_nr(struct backing_dev_info *bdi, struct bdi_writeback *wb)
+{
+	unsigned long mask = BDI_MAX_FLUSHERS - 1;
+	unsigned int nr;
+
+	do {
+		if ((bdi->wb_mask & mask) == mask)
+			return 1;
+
+		nr = find_first_zero_bit(&bdi->wb_mask, BDI_MAX_FLUSHERS);
+	} while (test_and_set_bit(nr, &bdi->wb_mask));
+
+	wb->nr = nr;
+
+	spin_lock(&bdi->wb_lock);
+	bdi->wb_cnt++;
+	spin_unlock(&bdi->wb_lock);
+
+	return 0;
+}
+
+static void bdi_put_wb(struct backing_dev_info *bdi, struct bdi_writeback *wb)
+{
+	/*
+	 * If this is the default wb thread exiting, leave the bit set
+	 * in the wb mask as we set that before it's created as well. This
+	 * is done to make sure that assigned work with no thread has at
+	 * least one receipient.
+	 */
+	if (wb == &bdi->wb)
+		clear_bit(BDI_wb_alloc, &bdi->state);
+	else {
+		clear_bit(wb->nr, &bdi->wb_mask);
+		kfree(wb);
+		spin_lock(&bdi->wb_lock);
+		bdi->wb_cnt--;
+		spin_unlock(&bdi->wb_lock);
+	}
+}
+
+static int bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
+{
+	memset(wb, 0, sizeof(*wb));
+
+	wb->bdi = bdi;
+	INIT_LIST_HEAD(&wb->b_dirty);
+	INIT_LIST_HEAD(&wb->b_io);
+	INIT_LIST_HEAD(&wb->b_more_io);
+
+	return wb_assign_nr(bdi, wb);
+}
+
+static struct bdi_writeback *bdi_new_wb(struct backing_dev_info *bdi)
+{
+	struct bdi_writeback *wb;
+
+	/*
+	 * Default bdi->wb is already assigned, so just return it
+	 */
+	if (!test_and_set_bit(BDI_wb_alloc, &bdi->state))
+		wb = &bdi->wb;
+	else {
+		wb = kmalloc(sizeof(struct bdi_writeback), GFP_KERNEL);
+		if (wb) {
+			if (bdi_wb_init(wb, bdi)) {
+				kfree(wb);
+				wb = NULL;
+			}
+		}
+	}
+
+	return wb;
+}
+
+static void bdi_task_init(struct backing_dev_info *bdi,
+			  struct bdi_writeback *wb)
+{
+	struct task_struct *tsk = current;
+	int was_empty;
+
+	/*
+	 * Add us to the active bdi_list. If we are adding threads beyond
+	 * the default embedded bdi_writeback, then we need to start using
+	 * proper locking. Check the list for empty first, then set the
+	 * BDI_wblist_lock flag if there's > 1 entry on the list now
+	 */
+	spin_lock(&bdi->wb_lock);
+
+	was_empty = list_empty(&bdi->wb_list);
+	list_add_tail_rcu(&wb->list, &bdi->wb_list);
+	if (!was_empty)
+		set_bit(BDI_wblist_lock, &bdi->state);
+
+	spin_unlock(&bdi->wb_lock);
+
+	tsk->flags |= PF_FLUSHER | PF_SWAPWRITE;
+	set_freezable();
+
+	/*
+	 * Our parent may run at a different priority, just set us to normal
+	 */
+	set_user_nice(tsk, 0);
+}
+
+static int bdi_start_fn(void *ptr)
+{
+	struct bdi_writeback *wb = ptr;
+	struct backing_dev_info *bdi = wb->bdi;
+	int ret;
+
+	/*
+	 * Add us to the active bdi_list
+	 */
+	spin_lock(&bdi_lock);
+	list_add(&bdi->bdi_list, &bdi_list);
+	spin_unlock(&bdi_lock);
+
+	bdi_task_init(bdi, wb);
+
+	/*
+	 * Clear pending bit and wakeup anybody waiting to tear us down
+	 */
+	clear_bit(BDI_pending, &bdi->state);
+	smp_mb__after_clear_bit();
+	wake_up_bit(&bdi->state, BDI_pending);
+
+	ret = bdi_writeback_task(wb);
+
+	/*
+	 * Remove us from the list
+	 */
+	spin_lock(&bdi->wb_lock);
+	list_del_rcu(&wb->list);
+	spin_unlock(&bdi->wb_lock);
+
+	/*
+	 * wait for rcu grace period to end, so we can free wb
+	 */
+	synchronize_srcu(&bdi->srcu);
+
+	bdi_put_wb(bdi, wb);
+	return ret;
+}
+
+int bdi_has_dirty_io(struct backing_dev_info *bdi)
+{
+	struct bdi_writeback *wb;
+	int ret = 0;
+
+	if (!bdi_wblist_needs_lock(bdi))
+		ret = wb_has_dirty_io(&bdi->wb);
+	else {
+		int idx;
+
+		idx = srcu_read_lock(&bdi->srcu);
+
+		list_for_each_entry_rcu(wb, &bdi->wb_list, list) {
+			ret = wb_has_dirty_io(wb);
+			if (ret)
+				break;
+		}
+
+		srcu_read_unlock(&bdi->srcu, idx);
+	}
+
+	return ret;
+}
+
+static void bdi_flush_io(struct backing_dev_info *bdi)
+{
+	struct writeback_control wbc = {
+		.bdi			= bdi,
+		.sync_mode		= WB_SYNC_NONE,
+		.older_than_this	= NULL,
+		.range_cyclic		= 1,
+		.nr_to_write		= 1024,
+	};
+
+	generic_sync_bdi_inodes(NULL, &wbc);
+}
+
+/*
+ * kupdated() used to do this. We cannot do it from the bdi_forker_task()
+ * 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 tasks 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;
+}
+
+static void arm_supers_timer(void)
+{
+	unsigned long next;
+
+	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);
+	arm_supers_timer();
+}
+
+static int bdi_forker_task(void *ptr)
+{
+	struct bdi_writeback *me = ptr;
+
+	bdi_task_init(me->bdi, me);
+
+	for (;;) {
+		struct backing_dev_info *bdi, *tmp;
+		struct bdi_writeback *wb;
+
+		/*
+		 * 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))
+			wb_do_writeback(me);
+
+		spin_lock(&bdi_lock);
+
+		/*
+		 * Check if any existing bdi's have dirty data without
+		 * a thread registered. If so, set that up.
+		 */
+		list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
+			if (bdi->wb.task || !bdi_has_dirty_io(bdi))
+				continue;
+
+			bdi_add_default_flusher_task(bdi);
+		}
+
+		set_current_state(TASK_INTERRUPTIBLE);
+
+		if (list_empty(&bdi_pending_list)) {
+			unsigned long wait;
+
+			spin_unlock(&bdi_lock);
+			wait = msecs_to_jiffies(dirty_writeback_interval * 10);
+			schedule_timeout(wait);
+			try_to_freeze();
+			continue;
+		}
+
+		__set_current_state(TASK_RUNNING);
+
+		/*
+		 * This is our real job - check for pending entries in
+		 * bdi_pending_list, and create the tasks that got added
+		 */
+		bdi = list_entry(bdi_pending_list.next, struct backing_dev_info,
+				 bdi_list);
+		list_del_init(&bdi->bdi_list);
+		spin_unlock(&bdi_lock);
+
+		wb = bdi_new_wb(bdi);
+		if (!wb)
+			goto readd_flush;
+
+		wb->task = kthread_run(bdi_start_fn, wb, "flush-%s",
+					dev_name(bdi->dev));
+
+		/*
+		 * If task creation fails, then readd the bdi to
+		 * the pending list and force writeout of the bdi
+		 * from this forker thread. That will free some memory
+		 * and we can try again.
+		 */
+		if (!wb->task) {
+			bdi_put_wb(bdi, wb);
+readd_flush:
+			/*
+			 * Add this 'bdi' to the back, so we get
+			 * a chance to flush other bdi's to free
+			 * memory.
+			 */
+			spin_lock(&bdi_lock);
+			list_add_tail(&bdi->bdi_list, &bdi_pending_list);
+			spin_unlock(&bdi_lock);
+
+			bdi_flush_io(bdi);
+		}
+	}
+
+	return 0;
+}
+
+/*
+ * bdi_lock held on entry
+ */
+static void bdi_add_one_flusher_task(struct backing_dev_info *bdi,
+				     int(*func)(struct backing_dev_info *))
+{
+	if (!bdi_cap_writeback_dirty(bdi))
+		return;
+
+	if (WARN_ON(!test_bit(BDI_registered, &bdi->state))) {
+		printk("bdi %p/%s is not registered!\n", bdi, bdi->name);
+		return;
+	}
+
+	/*
+	 * Check with the helper whether to proceed adding a task. Will only
+	 * abort if we two or more simultanous calls to
+	 * bdi_add_default_flusher_task() occured, further additions will block
+	 * waiting for previous additions to finish.
+	 */
+	if (!func(bdi)) {
+		list_move_tail(&bdi->bdi_list, &bdi_pending_list);
+
+		/*
+		 * We are now on the pending list, wake up bdi_forker_task()
+		 * to finish the job and add us back to the active bdi_list
+		 */
+		wake_up_process(default_backing_dev_info.wb.task);
+	}
+}
+
+static int flusher_add_helper_block(struct backing_dev_info *bdi)
+{
+	spin_unlock(&bdi_lock);
+	wait_on_bit_lock(&bdi->state, BDI_pending, bdi_sched_wait,
+				TASK_UNINTERRUPTIBLE);
+	spin_lock(&bdi_lock);
+	return 0;
+}
+
+static int flusher_add_helper_test(struct backing_dev_info *bdi)
+{
+	return test_and_set_bit(BDI_pending, &bdi->state);
+}
+
+/*
+ * Add the default flusher task that gets created for any bdi
+ * that has dirty data pending writeout
+ */
+void bdi_add_default_flusher_task(struct backing_dev_info *bdi)
+{
+	bdi_add_one_flusher_task(bdi, flusher_add_helper_test);
+}
+
+/**
+ * bdi_add_flusher_task - add one more flusher task to this @bdi
+ *  @bdi:	the bdi
+ *
+ * Add an additional flusher task to this @bdi. Will block waiting on
+ * previous additions, if any.
+ *
+ */
+void bdi_add_flusher_task(struct backing_dev_info *bdi)
+{
+	spin_lock(&bdi_lock);
+	bdi_add_one_flusher_task(bdi, flusher_add_helper_block);
+	spin_unlock(&bdi_lock);
+}
+EXPORT_SYMBOL(bdi_add_flusher_task);
+
 int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 		const char *fmt, ...)
 {
@@ -211,9 +635,41 @@ int bdi_register(struct backing_dev_info
 		goto exit;
 	}
 
+	spin_lock(&bdi_lock);
+	list_add_tail(&bdi->bdi_list, &bdi_list);
+	spin_unlock(&bdi_lock);
+
 	bdi->dev = dev;
-	bdi_debug_register(bdi, dev_name(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;
+
+		wb = bdi_new_wb(bdi);
+		if (!wb) {
+			ret = -ENOMEM;
+			goto remove_err;
+		}
+
+		wb->task = kthread_run(bdi_forker_task, wb, "bdi-%s",
+						dev_name(dev));
+		if (!wb->task) {
+			bdi_put_wb(bdi, wb);
+			ret = -ENOMEM;
+remove_err:
+			spin_lock(&bdi_lock);
+			list_del(&bdi->bdi_list);
+			spin_unlock(&bdi_lock);
+			goto exit;
+		}
+	}
+
+	bdi_debug_register(bdi, dev_name(dev));
+	set_bit(BDI_registered, &bdi->state);
 exit:
 	return ret;
 }
@@ -225,9 +681,42 @@ int bdi_register_dev(struct backing_dev_
 }
 EXPORT_SYMBOL(bdi_register_dev);
 
+/*
+ * Remove bdi from global list and shutdown any threads we have running
+ */
+static void bdi_wb_shutdown(struct backing_dev_info *bdi)
+{
+	struct bdi_writeback *wb;
+
+	if (!bdi_cap_writeback_dirty(bdi))
+		return;
+
+	/*
+	 * If setup is pending, wait for that to complete first
+	 */
+	wait_on_bit(&bdi->state, BDI_pending, bdi_sched_wait,
+			TASK_UNINTERRUPTIBLE);
+
+	/*
+	 * Make sure nobody finds us on the bdi_list anymore
+	 */
+	spin_lock(&bdi_lock);
+	list_del(&bdi->bdi_list);
+	spin_unlock(&bdi_lock);
+
+	/*
+	 * Finally, kill the kernel threads. We don't need to be RCU
+	 * safe anymore, since the bdi is gone from visibility.
+	 */
+	list_for_each_entry(wb, &bdi->wb_list, list)
+		kthread_stop(wb->task);
+}
+
 void bdi_unregister(struct backing_dev_info *bdi)
 {
 	if (bdi->dev) {
+		if (!bdi_cap_flush_forker(bdi))
+			bdi_wb_shutdown(bdi);
 		bdi_debug_unregister(bdi);
 		device_unregister(bdi->dev);
 		bdi->dev = NULL;
@@ -237,14 +726,21 @@ EXPORT_SYMBOL(bdi_unregister);
 
 int bdi_init(struct backing_dev_info *bdi)
 {
-	int i;
-	int err;
+	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);
+	bdi->wb_mask = 0;
+	bdi->wb_cnt = 0;
+	INIT_LIST_HEAD(&bdi->bdi_list);
+	INIT_LIST_HEAD(&bdi->wb_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);
@@ -252,10 +748,15 @@ int bdi_init(struct backing_dev_info *bd
 			goto err;
 	}
 
+	err = init_srcu_struct(&bdi->srcu);
+	if (err)
+		goto err;
+
 	bdi->dirty_exceeded = 0;
 	err = prop_local_init_percpu(&bdi->completions);
 
 	if (err) {
+		cleanup_srcu_struct(&bdi->srcu);
 err:
 		while (i--)
 			percpu_counter_destroy(&bdi->bdi_stat[i]);
@@ -269,8 +770,12 @@ void bdi_destroy(struct backing_dev_info
 {
 	int i;
 
+	WARN_ON(bdi_has_dirty_io(bdi));
+
 	bdi_unregister(bdi);
 
+	cleanup_srcu_struct(&bdi->srcu);
+
 	for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
 		percpu_counter_destroy(&bdi->bdi_stat[i]);
 
diff -Nraup linux-2.6.30/mm/Makefile linux-2.6.30_bdiflusherv10/mm/Makefile
--- linux-2.6.30/mm/Makefile	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/mm/Makefile	2009-06-15 15:52:50.000000000 +0800
@@ -8,7 +8,7 @@ mmu-$(CONFIG_MMU)	:= fremap.o highmem.o 
 			   vmalloc.o
 
 obj-y			:= bootmem.o filemap.o mempool.o oom_kill.o fadvise.o \
-			   maccess.o page_alloc.o page-writeback.o pdflush.o \
+			   maccess.o page_alloc.o page-writeback.o \
 			   readahead.o swap.o truncate.o vmscan.o shmem.o \
 			   prio_tree.o util.o mmzone.o vmstat.o backing-dev.o \
 			   page_isolation.o mm_init.o $(mmu-y)
diff -Nraup linux-2.6.30/mm/page-writeback.c linux-2.6.30_bdiflusherv10/mm/page-writeback.c
--- linux-2.6.30/mm/page-writeback.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/mm/page-writeback.c	2009-06-15 15:52:50.000000000 +0800
@@ -36,15 +36,6 @@
 #include <linux/pagevec.h>
 
 /*
- * The maximum number of pages to writeout in a single bdflush/kupdate
- * operation.  We do this so we don't hold I_SYNC 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.
  */
@@ -117,8 +108,6 @@ EXPORT_SYMBOL(laptop_mode);
 /* End of sysctl-exported parameters */
 
 
-static void background_writeout(unsigned long _min_pages);
-
 /*
  * Scale the writeback cache size proportional to the relative writeout speeds.
  *
@@ -319,15 +308,13 @@ static void task_dirty_limit(struct task
 /*
  *
  */
-static DEFINE_SPINLOCK(bdi_lock);
 static unsigned int bdi_min_ratio;
 
 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
 {
 	int ret = 0;
-	unsigned long flags;
 
-	spin_lock_irqsave(&bdi_lock, flags);
+	spin_lock(&bdi_lock);
 	if (min_ratio > bdi->max_ratio) {
 		ret = -EINVAL;
 	} else {
@@ -339,27 +326,26 @@ int bdi_set_min_ratio(struct backing_dev
 			ret = -EINVAL;
 		}
 	}
-	spin_unlock_irqrestore(&bdi_lock, flags);
+	spin_unlock(&bdi_lock);
 
 	return ret;
 }
 
 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
 {
-	unsigned long flags;
 	int ret = 0;
 
 	if (max_ratio > 100)
 		return -EINVAL;
 
-	spin_lock_irqsave(&bdi_lock, flags);
+	spin_lock(&bdi_lock);
 	if (bdi->min_ratio > max_ratio) {
 		ret = -EINVAL;
 	} else {
 		bdi->max_ratio = max_ratio;
 		bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
 	}
-	spin_unlock_irqrestore(&bdi_lock, flags);
+	spin_unlock(&bdi_lock);
 
 	return ret;
 }
@@ -542,7 +528,7 @@ static void balance_dirty_pages(struct a
 		 * been flushed to permanent storage.
 		 */
 		if (bdi_nr_reclaimable) {
-			writeback_inodes(&wbc);
+			generic_sync_bdi_inodes(NULL, &wbc);
 			pages_written += write_chunk - wbc.nr_to_write;
 			get_dirty_limits(&background_thresh, &dirty_thresh,
 				       &bdi_thresh, bdi);
@@ -593,7 +579,7 @@ static void balance_dirty_pages(struct a
 			(!laptop_mode && (global_page_state(NR_FILE_DIRTY)
 					  + global_page_state(NR_UNSTABLE_NFS)
 					  > background_thresh)))
-		pdflush_operation(background_writeout, 0);
+		bdi_start_writeback(bdi, NULL, 0, WB_SYNC_NONE);
 }
 
 void set_page_dirty_balance(struct page *page, int page_mkwrite)
@@ -678,152 +664,53 @@ void throttle_vm_writeout(gfp_t gfp_mask
 }
 
 /*
- * 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.
+ * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
+ * the whole world.
  */
-static void background_writeout(unsigned long _min_pages)
+void wakeup_flusher_threads(long nr_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,
 		.range_cyclic	= 1,
 	};
 
-	for ( ; ; ) {
-		unsigned long background_thresh;
-		unsigned long dirty_thresh;
-
-		get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
-		if (global_page_state(NR_FILE_DIRTY) +
-			global_page_state(NR_UNSTABLE_NFS) < background_thresh
-				&& min_pages <= 0)
-			break;
-		wbc.more_io = 0;
-		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 */
-			if (wbc.encountered_congestion || wbc.more_io)
-				congestion_wait(WRITE, HZ/10);
-			else
-				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_pdflush(long nr_pages)
-{
 	if (nr_pages == 0)
 		nr_pages = global_page_state(NR_FILE_DIRTY) +
 				global_page_state(NR_UNSTABLE_NFS);
-	return pdflush_operation(background_writeout, nr_pages);
+	wbc.nr_to_write = nr_pages;
+	bdi_writeback_all(NULL, &wbc);
 }
 
-static void wb_timer_fn(unsigned long unused);
 static void laptop_timer_fn(unsigned long unused);
 
-static DEFINE_TIMER(wb_timer, wb_timer_fn, 0, 0);
 static DEFINE_TIMER(laptop_mode_wb_timer, 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_interval.  But if a writeback event
- * takes longer than a dirty_writeback_interval 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_control wbc = {
-		.bdi		= NULL,
-		.sync_mode	= WB_SYNC_NONE,
-		.older_than_this = &oldest_jif,
-		.nr_to_write	= 0,
-		.nonblocking	= 1,
-		.for_kupdate	= 1,
-		.range_cyclic	= 1,
-	};
-
-	sync_supers();
-
-	oldest_jif = jiffies - msecs_to_jiffies(dirty_expire_interval * 10);
-	start_jif = jiffies;
-	next_jif = start_jif + msecs_to_jiffies(dirty_writeback_interval * 10);
-	nr_to_write = global_page_state(NR_FILE_DIRTY) +
-			global_page_state(NR_UNSTABLE_NFS) +
-			(inodes_stat.nr_inodes - inodes_stat.nr_unused);
-	while (nr_to_write > 0) {
-		wbc.more_io = 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 || wbc.more_io)
-				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_interval)
-		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_interval)
-		mod_timer(&wb_timer, jiffies +
-			msecs_to_jiffies(dirty_writeback_interval * 10));
-	else
-		del_timer(&wb_timer);
 	return 0;
 }
 
-static void wb_timer_fn(unsigned long unused)
+static void do_laptop_sync(struct work_struct *work)
 {
-	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();
+	wakeup_flusher_threads(0);
+	kfree(work);
 }
 
 static void laptop_timer_fn(unsigned long unused)
 {
-	pdflush_operation(laptop_flush, 0);
+	struct work_struct *work;
+
+	work = kmalloc(sizeof(*work), GFP_ATOMIC);
+	if (work) {
+		INIT_WORK(work, do_laptop_sync);
+		schedule_work(work);
+	}
 }
 
 /*
@@ -906,8 +793,6 @@ void __init page_writeback_init(void)
 {
 	int shift;
 
-	mod_timer(&wb_timer,
-		  jiffies + msecs_to_jiffies(dirty_writeback_interval * 10));
 	writeback_set_ratelimit();
 	register_cpu_notifier(&ratelimit_nb);
 
diff -Nraup linux-2.6.30/mm/pdflush.c linux-2.6.30_bdiflusherv10/mm/pdflush.c
--- linux-2.6.30/mm/pdflush.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/mm/pdflush.c	1970-01-01 08:00:00.000000000 +0800
@@ -1,269 +0,0 @@
-/*
- * mm/pdflush.c - worker threads for writing back filesystem data
- *
- * Copyright (C) 2002, Linus Torvalds.
- *
- * 09Apr2002	Andrew Morton
- *		Initial version
- * 29Feb2004	kaos@sgi.com
- *		Move worker thread creation to kthread to avoid chewing
- *		up stack space with nested calls to kernel_thread.
- */
-
-#include <linux/sched.h>
-#include <linux/list.h>
-#include <linux/signal.h>
-#include <linux/spinlock.h>
-#include <linux/gfp.h>
-#include <linux/init.h>
-#include <linux/module.h>
-#include <linux/fs.h>		/* Needed by writeback.h	  */
-#include <linux/writeback.h>	/* Prototypes pdflush_operation() */
-#include <linux/kthread.h>
-#include <linux/cpuset.h>
-#include <linux/freezer.h>
-
-
-/*
- * Minimum and maximum number of pdflush instances
- */
-#define MIN_PDFLUSH_THREADS	2
-#define MAX_PDFLUSH_THREADS	8
-
-static void start_one_pdflush_thread(void);
-
-
-/*
- * The pdflush threads are worker threads for writing back dirty data.
- * Ideally, we'd like one thread per active disk spindle.  But the disk
- * topology is very hard to divine at this level.   Instead, we take
- * care in various places to prevent more than one pdflush thread from
- * performing writeback against a single filesystem.  pdflush threads
- * have the PF_FLUSHER flag set in current->flags to aid in this.
- */
-
-/*
- * All the pdflush threads.  Protected by pdflush_lock
- */
-static LIST_HEAD(pdflush_list);
-static DEFINE_SPINLOCK(pdflush_lock);
-
-/*
- * The count of currently-running pdflush threads.  Protected
- * by pdflush_lock.
- *
- * Readable by sysctl, but not writable.  Published to userspace at
- * /proc/sys/vm/nr_pdflush_threads.
- */
-int nr_pdflush_threads = 0;
-
-/*
- * The time at which the pdflush thread pool last went empty
- */
-static unsigned long last_empty_jifs;
-
-/*
- * The pdflush thread.
- *
- * Thread pool management algorithm:
- * 
- * - The minimum and maximum number of pdflush instances are bound
- *   by MIN_PDFLUSH_THREADS and MAX_PDFLUSH_THREADS.
- * 
- * - If there have been no idle pdflush instances for 1 second, create
- *   a new one.
- * 
- * - If the least-recently-went-to-sleep pdflush thread has been asleep
- *   for more than one second, terminate a thread.
- */
-
-/*
- * A structure for passing work to a pdflush thread.  Also for passing
- * state information between pdflush threads.  Protected by pdflush_lock.
- */
-struct pdflush_work {
-	struct task_struct *who;	/* The thread */
-	void (*fn)(unsigned long);	/* A callback function */
-	unsigned long arg0;		/* An argument to the callback */
-	struct list_head list;		/* On pdflush_list, when idle */
-	unsigned long when_i_went_to_sleep;
-};
-
-static int __pdflush(struct pdflush_work *my_work)
-{
-	current->flags |= PF_FLUSHER | PF_SWAPWRITE;
-	set_freezable();
-	my_work->fn = NULL;
-	my_work->who = current;
-	INIT_LIST_HEAD(&my_work->list);
-
-	spin_lock_irq(&pdflush_lock);
-	for ( ; ; ) {
-		struct pdflush_work *pdf;
-
-		set_current_state(TASK_INTERRUPTIBLE);
-		list_move(&my_work->list, &pdflush_list);
-		my_work->when_i_went_to_sleep = jiffies;
-		spin_unlock_irq(&pdflush_lock);
-		schedule();
-		try_to_freeze();
-		spin_lock_irq(&pdflush_lock);
-		if (!list_empty(&my_work->list)) {
-			/*
-			 * Someone woke us up, but without removing our control
-			 * structure from the global list.  swsusp will do this
-			 * in try_to_freeze()->refrigerator().  Handle it.
-			 */
-			my_work->fn = NULL;
-			continue;
-		}
-		if (my_work->fn == NULL) {
-			printk("pdflush: bogus wakeup\n");
-			continue;
-		}
-		spin_unlock_irq(&pdflush_lock);
-
-		(*my_work->fn)(my_work->arg0);
-
-		spin_lock_irq(&pdflush_lock);
-
-		/*
-		 * Thread creation: For how long have there been zero
-		 * available threads?
-		 *
-		 * To throttle creation, we reset last_empty_jifs.
-		 */
-		if (time_after(jiffies, last_empty_jifs + 1 * HZ)) {
-			if (list_empty(&pdflush_list)) {
-				if (nr_pdflush_threads < MAX_PDFLUSH_THREADS) {
-					last_empty_jifs = jiffies;
-					nr_pdflush_threads++;
-					spin_unlock_irq(&pdflush_lock);
-					start_one_pdflush_thread();
-					spin_lock_irq(&pdflush_lock);
-				}
-			}
-		}
-
-		my_work->fn = NULL;
-
-		/*
-		 * Thread destruction: For how long has the sleepiest
-		 * thread slept?
-		 */
-		if (list_empty(&pdflush_list))
-			continue;
-		if (nr_pdflush_threads <= MIN_PDFLUSH_THREADS)
-			continue;
-		pdf = list_entry(pdflush_list.prev, struct pdflush_work, list);
-		if (time_after(jiffies, pdf->when_i_went_to_sleep + 1 * HZ)) {
-			/* Limit exit rate */
-			pdf->when_i_went_to_sleep = jiffies;
-			break;					/* exeunt */
-		}
-	}
-	nr_pdflush_threads--;
-	spin_unlock_irq(&pdflush_lock);
-	return 0;
-}
-
-/*
- * Of course, my_work wants to be just a local in __pdflush().  It is
- * separated out in this manner to hopefully prevent the compiler from
- * performing unfortunate optimisations against the auto variables.  Because
- * these are visible to other tasks and CPUs.  (No problem has actually
- * been observed.  This is just paranoia).
- */
-static int pdflush(void *dummy)
-{
-	struct pdflush_work my_work;
-	cpumask_var_t cpus_allowed;
-
-	/*
-	 * Since the caller doesn't even check kthread_run() worked, let's not
-	 * freak out too much if this fails.
-	 */
-	if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL)) {
-		printk(KERN_WARNING "pdflush failed to allocate cpumask\n");
-		return 0;
-	}
-
-	/*
-	 * pdflush can spend a lot of time doing encryption via dm-crypt.  We
-	 * don't want to do that at keventd's priority.
-	 */
-	set_user_nice(current, 0);
-
-	/*
-	 * Some configs put our parent kthread in a limited cpuset,
-	 * which kthread() overrides, forcing cpus_allowed == cpu_all_mask.
-	 * Our needs are more modest - cut back to our cpusets cpus_allowed.
-	 * This is needed as pdflush's are dynamically created and destroyed.
-	 * The boottime pdflush's are easily placed w/o these 2 lines.
-	 */
-	cpuset_cpus_allowed(current, cpus_allowed);
-	set_cpus_allowed_ptr(current, cpus_allowed);
-	free_cpumask_var(cpus_allowed);
-
-	return __pdflush(&my_work);
-}
-
-/*
- * Attempt to wake up a pdflush thread, and get it to do some work for you.
- * Returns zero if it indeed managed to find a worker thread, and passed your
- * payload to it.
- */
-int pdflush_operation(void (*fn)(unsigned long), unsigned long arg0)
-{
-	unsigned long flags;
-	int ret = 0;
-
-	BUG_ON(fn == NULL);	/* Hard to diagnose if it's deferred */
-
-	spin_lock_irqsave(&pdflush_lock, flags);
-	if (list_empty(&pdflush_list)) {
-		ret = -1;
-	} else {
-		struct pdflush_work *pdf;
-
-		pdf = list_entry(pdflush_list.next, struct pdflush_work, list);
-		list_del_init(&pdf->list);
-		if (list_empty(&pdflush_list))
-			last_empty_jifs = jiffies;
-		pdf->fn = fn;
-		pdf->arg0 = arg0;
-		wake_up_process(pdf->who);
-	}
-	spin_unlock_irqrestore(&pdflush_lock, flags);
-
-	return ret;
-}
-
-static void start_one_pdflush_thread(void)
-{
-	struct task_struct *k;
-
-	k = kthread_run(pdflush, NULL, "pdflush");
-	if (unlikely(IS_ERR(k))) {
-		spin_lock_irq(&pdflush_lock);
-		nr_pdflush_threads--;
-		spin_unlock_irq(&pdflush_lock);
-	}
-}
-
-static int __init pdflush_init(void)
-{
-	int i;
-
-	/*
-	 * Pre-set nr_pdflush_threads...  If we fail to create,
-	 * the count will be decremented.
-	 */
-	nr_pdflush_threads = MIN_PDFLUSH_THREADS;
-
-	for (i = 0; i < MIN_PDFLUSH_THREADS; i++)
-		start_one_pdflush_thread();
-	return 0;
-}
-
-module_init(pdflush_init);
diff -Nraup linux-2.6.30/mm/swap_state.c linux-2.6.30_bdiflusherv10/mm/swap_state.c
--- linux-2.6.30/mm/swap_state.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/mm/swap_state.c	2009-06-15 15:52:50.000000000 +0800
@@ -34,6 +34,7 @@ static const struct address_space_operat
 };
 
 static struct backing_dev_info swap_backing_dev_info = {
+	.name		= "swap",
 	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
 	.unplug_io_fn	= swap_unplug_io_fn,
 };
diff -Nraup linux-2.6.30/mm/vmscan.c linux-2.6.30_bdiflusherv10/mm/vmscan.c
--- linux-2.6.30/mm/vmscan.c	2009-06-10 11:05:27.000000000 +0800
+++ linux-2.6.30_bdiflusherv10/mm/vmscan.c	2009-06-15 15:52:50.000000000 +0800
@@ -1656,7 +1656,7 @@ static unsigned long do_try_to_free_page
 		 */
 		if (total_scanned > sc->swap_cluster_max +
 					sc->swap_cluster_max / 2) {
-			wakeup_pdflush(laptop_mode ? 0 : total_scanned);
+			wakeup_flusher_threads(laptop_mode ? 0 : total_scanned);
 			sc->may_writepage = 1;
 		}
 

Re: [PATCH 0/15] Per-bdi writeback flusher threads v10

[Jens Axboe]

On Tue, Jun 16 2009, Zhang, Yanmin wrote:
> On Fri, 2009-06-12 at 14:54 +0200, Jens Axboe wrote:
> > Hi,
> > 
> > Here's the 10th version of the writeback patches. Changes since v9:
> > 
> > - Fix bdi task exit race leaving work on the list, flush it after we
> >   know we cannot be found anymore.
> > - Rename flusher tasks from bdi-foo to flush-foo. Should make it more
> >   clear to the casual observer.
> > - Fix a problem with the btrfs bdi register patch that would spew
> >   warnings for > 1 mounted btrfs file system.
> > - Rebase to current -git, there were some conflicts with the latest work
> >   from viro/hch.
> > - Fix a block layer core problem were stacked devices would overwrite
> >   the bdi state, causing problems and warning spew.
> > - In bdi_writeback_all(), in the race occurence of a work allocation
> >   failure, restart scanning from the beginning. Then we can drop the
> >   bdi_lock mutex before diving into bdi specific writeback.
> > - Convert bdi_lock to a spinlock.
> > - Use spin_trylock() in bdi_writeback_all(), if this isn't a data
> >   integrity writeback. Debatable, I kind of like it...
> > - Get rid of BDI_CAP_FLUSH_FORKER, just check for match with the
> >   default_backing_dev_info.
> > - Fix race in list checking in bdi_forker_task().
> > 
> > 
> > For ease of patching, I've put the full diff here:
> > 
> >   http://kernel.dk/writeback-v10.patch
> Jens,
> 
> I applied the patch to 2.6.30 and got a confliction. The attachment is
> the patch I ported to 2.6.30. Did I miss anything?
> 
> 
> With the patch, kernel reports below messages on 2 machines.
> 
> INFO: task sync:29984 blocked for more than 120 seconds.
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> sync          D ffff88002805e300  6168 29984  24581
>  ffff88022f84b780 0000000000000082 7fffffffffffffff ffff880133dbfe70
>  0000000000000000 ffff88022e2b4c50 ffff88022e2b4fd8 00000001000c7bb8
>  ffff88022f513fd0 ffff880133dbfde8 ffff880133dbfec8 ffff88022d5d13c8
> Call Trace:
>  [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
>  [<ffffffff80780fde>] ? schedule+0x9/0x1d
>  [<ffffffff802b69ed>] ? bdi_sched_wait+0x9/0xd
>  [<ffffffff8078158d>] ? __wait_on_bit+0x40/0x6f
>  [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
>  [<ffffffff80781628>] ? out_of_line_wait_on_bit+0x6c/0x78
>  [<ffffffff8024a426>] ? wake_bit_function+0x0/0x23
>  [<ffffffff802b67ac>] ? bdi_writeback_all+0x12a/0x152
>  [<ffffffff802b6805>] ? generic_sync_sb_inodes+0x31/0xde
>  [<ffffffff802b6935>] ? sync_inodes_sb+0x83/0x88
>  [<ffffffff802b6980>] ? __sync_inodes+0x46/0x8f
>  [<ffffffff802b94f2>] ? do_sync+0x36/0x5a
>  [<ffffffff802b9538>] ? sys_sync+0xe/0x12
>  [<ffffffff8020b9ab>] ? system_call_fastpath+0x16/0x1b

I don't think it is your backport, for some reason the v10 missed a
change that I think could solve this race. If not, there's another in
there that I need to look at.

So against your current base, could you try with the below added as
well? The printk() is just so we can see if this triggers for you or
not.

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index b3e80c5..a065da5 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -384,6 +384,15 @@ static int bdi_start_fn(void *ptr)
 	 */
 	synchronize_srcu(&bdi->srcu);
 
+	/*
+	 * Flush any pending work. No more can be added, since
+	 * the bdi is no longer discoverable.
+	 */
+	if (!list_empty(&bdi->work_list)) {
+		printk("bdi: flushing racy work\n");
+		wb_do_writeback(wb);
+	}
+
 	bdi_put_wb(bdi, wb);
 	return ret;
 }

-- 
Jens Axboe

Re: [PATCH 0/15] Per-bdi writeback flusher threads v10

[Jens Axboe]

On Tue, Jun 16 2009, Jens Axboe wrote:
> On Tue, Jun 16 2009, Zhang, Yanmin wrote:
> > On Fri, 2009-06-12 at 14:54 +0200, Jens Axboe wrote:
> > > Hi,
> > > 
> > > Here's the 10th version of the writeback patches. Changes since v9:
> > > 
> > > - Fix bdi task exit race leaving work on the list, flush it after we
> > >   know we cannot be found anymore.
> > > - Rename flusher tasks from bdi-foo to flush-foo. Should make it more
> > >   clear to the casual observer.
> > > - Fix a problem with the btrfs bdi register patch that would spew
> > >   warnings for > 1 mounted btrfs file system.
> > > - Rebase to current -git, there were some conflicts with the latest work
> > >   from viro/hch.
> > > - Fix a block layer core problem were stacked devices would overwrite
> > >   the bdi state, causing problems and warning spew.
> > > - In bdi_writeback_all(), in the race occurence of a work allocation
> > >   failure, restart scanning from the beginning. Then we can drop the
> > >   bdi_lock mutex before diving into bdi specific writeback.
> > > - Convert bdi_lock to a spinlock.
> > > - Use spin_trylock() in bdi_writeback_all(), if this isn't a data
> > >   integrity writeback. Debatable, I kind of like it...
> > > - Get rid of BDI_CAP_FLUSH_FORKER, just check for match with the
> > >   default_backing_dev_info.
> > > - Fix race in list checking in bdi_forker_task().
> > > 
> > > 
> > > For ease of patching, I've put the full diff here:
> > > 
> > >   http://kernel.dk/writeback-v10.patch
> > Jens,
> > 
> > I applied the patch to 2.6.30 and got a confliction. The attachment is
> > the patch I ported to 2.6.30. Did I miss anything?
> > 
> > 
> > With the patch, kernel reports below messages on 2 machines.
> > 
> > INFO: task sync:29984 blocked for more than 120 seconds.
> > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > sync          D ffff88002805e300  6168 29984  24581
> >  ffff88022f84b780 0000000000000082 7fffffffffffffff ffff880133dbfe70
> >  0000000000000000 ffff88022e2b4c50 ffff88022e2b4fd8 00000001000c7bb8
> >  ffff88022f513fd0 ffff880133dbfde8 ffff880133dbfec8 ffff88022d5d13c8
> > Call Trace:
> >  [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
> >  [<ffffffff80780fde>] ? schedule+0x9/0x1d
> >  [<ffffffff802b69ed>] ? bdi_sched_wait+0x9/0xd
> >  [<ffffffff8078158d>] ? __wait_on_bit+0x40/0x6f
> >  [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
> >  [<ffffffff80781628>] ? out_of_line_wait_on_bit+0x6c/0x78
> >  [<ffffffff8024a426>] ? wake_bit_function+0x0/0x23
> >  [<ffffffff802b67ac>] ? bdi_writeback_all+0x12a/0x152
> >  [<ffffffff802b6805>] ? generic_sync_sb_inodes+0x31/0xde
> >  [<ffffffff802b6935>] ? sync_inodes_sb+0x83/0x88
> >  [<ffffffff802b6980>] ? __sync_inodes+0x46/0x8f
> >  [<ffffffff802b94f2>] ? do_sync+0x36/0x5a
> >  [<ffffffff802b9538>] ? sys_sync+0xe/0x12
> >  [<ffffffff8020b9ab>] ? system_call_fastpath+0x16/0x1b
> 
> I don't think it is your backport, for some reason the v10 missed a
> change that I think could solve this race. If not, there's another in
> there that I need to look at.
> 
> So against your current base, could you try with the below added as
> well? The printk() is just so we can see if this triggers for you or
> not.

OK that wont work, since we need to actually wait for the work to be
flushed, otherwise we wreak things when we free the bdi immediately
after that.

Can you try with this patch?

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 5a1837f..4a6859e 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -409,7 +409,7 @@ static struct bdi_work *get_next_work_item(struct backing_dev_info *bdi,
 /*
  * Retrieve work items and do the writeback they describe
  */
-static long wb_writeback(struct bdi_writeback *wb)
+static long wb_writeback(struct bdi_writeback *wb, int force_wait)
 {
 	struct backing_dev_info *bdi = wb->bdi;
 	struct bdi_work *work;
@@ -418,7 +418,12 @@ static long wb_writeback(struct bdi_writeback *wb)
 	while ((work = get_next_work_item(bdi, wb)) != NULL) {
 		struct super_block *sb = bdi_work_sb(work);
 		long nr_pages = work->nr_pages;
-		enum writeback_sync_modes sync_mode = work->sync_mode;
+		enum writeback_sync_modes sync_mode;
+
+		if (force_wait)
+			sync_mode = WB_SYNC_ALL;
+		else
+			sync_mode = work->sync_mode;
 
 		/*
 		 * If this isn't a data integrity operation, just notify
@@ -444,7 +449,7 @@ static long wb_writeback(struct bdi_writeback *wb)
  * This will be inlined in bdi_writeback_task() once we get rid of any
  * dirty inodes on the default_backing_dev_info
  */
-long wb_do_writeback(struct bdi_writeback *wb)
+long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
 {
 	long wrote;
 
@@ -461,7 +466,7 @@ long wb_do_writeback(struct bdi_writeback *wb)
 	if (list_empty(&wb->bdi->work_list))
 		wrote = wb_kupdated(wb);
 	else
-		wrote = wb_writeback(wb);
+		wrote = wb_writeback(wb, force_wait);
 
 	return wrote;
 }
@@ -477,7 +482,7 @@ int bdi_writeback_task(struct bdi_writeback *wb)
 	long pages_written;
 
 	while (!kthread_should_stop()) {
-		pages_written = wb_do_writeback(wb);
+		pages_written = wb_do_writeback(wb, 0);
 
 		if (pages_written)
 			last_active = jiffies;
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 0d4e31d..e070b91 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -68,7 +68,7 @@ struct writeback_control {
 void writeback_inodes(struct writeback_control *wbc);
 int inode_wait(void *);
 void sync_inodes_sb(struct super_block *, int wait);
-long wb_do_writeback(struct bdi_writeback *wb);
+long wb_do_writeback(struct bdi_writeback *wb, int force_wait);
 
 /* writeback.h requires fs.h; it, too, is not included from here. */
 static inline void wait_on_inode(struct inode *inode)
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 23013d5..0c91add 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -389,7 +389,7 @@ static int bdi_start_fn(void *ptr)
 	 * will be added, since this bdi isn't discoverable anymore.
 	 */
 	if (!list_empty(&bdi->work_list))
-		wb_do_writeback(wb);
+		wb_do_writeback(wb, 1);
 
 	bdi_put_wb(bdi, wb);
 	return ret;
@@ -484,7 +484,7 @@ static int bdi_forker_task(void *ptr)
 		 * dirty data on the default backing_dev_info
 		 */
 		if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list))
-			wb_do_writeback(me);
+			wb_do_writeback(me, 0);
 
 		spin_lock(&bdi_lock);
 

-- 
Jens Axboe

Re: [PATCH 0/15] Per-bdi writeback flusher threads v10

[Zhang, Yanmin]

On Tue, 2009-06-16 at 21:53 +0200, Jens Axboe wrote:
> On Tue, Jun 16 2009, Jens Axboe wrote:
> > On Tue, Jun 16 2009, Zhang, Yanmin wrote:
> > > On Fri, 2009-06-12 at 14:54 +0200, Jens Axboe wrote:
> > > > Hi,
> > > > 
> > > > Here's the 10th version of the writeback patches. Changes since v9:
> > > > 
> > > > - Fix bdi task exit race leaving work on the list, flush it after we
> > > >   know we cannot be found anymore.
> > > > - Rename flusher tasks from bdi-foo to flush-foo. Should make it more
> > > >   clear to the casual observer.
> > > > - Fix a problem with the btrfs bdi register patch that would spew
> > > >   warnings for > 1 mounted btrfs file system.
> > > > - Rebase to current -git, there were some conflicts with the latest work
> > > >   from viro/hch.
> > > > - Fix a block layer core problem were stacked devices would overwrite
> > > >   the bdi state, causing problems and warning spew.
> > > > - In bdi_writeback_all(), in the race occurence of a work allocation
> > > >   failure, restart scanning from the beginning. Then we can drop the
> > > >   bdi_lock mutex before diving into bdi specific writeback.
> > > > - Convert bdi_lock to a spinlock.
> > > > - Use spin_trylock() in bdi_writeback_all(), if this isn't a data
> > > >   integrity writeback. Debatable, I kind of like it...
> > > > - Get rid of BDI_CAP_FLUSH_FORKER, just check for match with the
> > > >   default_backing_dev_info.
> > > > - Fix race in list checking in bdi_forker_task().
> > > > 
> > > > 
> > > > For ease of patching, I've put the full diff here:
> > > > 
> > > >   http://kernel.dk/writeback-v10.patch
> > > Jens,
> > > 
> > > I applied the patch to 2.6.30 and got a confliction. The attachment is
> > > the patch I ported to 2.6.30. Did I miss anything?
> > > 
> > > 
> > > With the patch, kernel reports below messages on 2 machines.
> > > 
> > > INFO: task sync:29984 blocked for more than 120 seconds.
> > > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > > sync          D ffff88002805e300  6168 29984  24581
> > >  ffff88022f84b780 0000000000000082 7fffffffffffffff ffff880133dbfe70
> > >  0000000000000000 ffff88022e2b4c50 ffff88022e2b4fd8 00000001000c7bb8
> > >  ffff88022f513fd0 ffff880133dbfde8 ffff880133dbfec8 ffff88022d5d13c8
> > > Call Trace:
> > >  [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
> > >  [<ffffffff80780fde>] ? schedule+0x9/0x1d
> > >  [<ffffffff802b69ed>] ? bdi_sched_wait+0x9/0xd
> > >  [<ffffffff8078158d>] ? __wait_on_bit+0x40/0x6f
> > >  [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
> > >  [<ffffffff80781628>] ? out_of_line_wait_on_bit+0x6c/0x78
> > >  [<ffffffff8024a426>] ? wake_bit_function+0x0/0x23
> > >  [<ffffffff802b67ac>] ? bdi_writeback_all+0x12a/0x152
> > >  [<ffffffff802b6805>] ? generic_sync_sb_inodes+0x31/0xde
> > >  [<ffffffff802b6935>] ? sync_inodes_sb+0x83/0x88
> > >  [<ffffffff802b6980>] ? __sync_inodes+0x46/0x8f
> > >  [<ffffffff802b94f2>] ? do_sync+0x36/0x5a
> > >  [<ffffffff802b9538>] ? sys_sync+0xe/0x12
> > >  [<ffffffff8020b9ab>] ? system_call_fastpath+0x16/0x1b
> > 
> > I don't think it is your backport, for some reason the v10 missed a
> > change that I think could solve this race. If not, there's another in
> > there that I need to look at.
> > 
> > So against your current base, could you try with the below added as
> > well? The printk() is just so we can see if this triggers for you or
> > not.
> 
> OK that wont work, since we need to actually wait for the work to be
> flushed, otherwise we wreak things when we free the bdi immediately
> after that.
> 
> Can you try with this patch?
Jens,

I tested below patch on 4 machines (run all fio sub-test cases twice which
need more than 10 hours). The previous 2 machines don't stop this time.
Unfortunately, the 3rd machine stops. I double-check the disassembled codes
of kernel and make sure bdi_start_fn really calls wb_do_writeback.

INFO: task sync:30618 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
sync          D ffffc20000011300  4736 30618  28522
 ffff8800bd25b090 0000000000000082 ffff8800bd763780 ffff8800bd763b08
 00000000bd582e68 0000000000004000 0000000000011300 000000000000c868
 ffff8800bd9c5df8 0000000000000000 ffff8800bd763780 ffff8800bd763b08
Call Trace:
 [<ffffffff802784ba>] ? find_get_pages_tag+0x46/0xdd
 [<ffffffff802c3297>] ? bdi_sched_wait+0x0/0xd
 [<ffffffff80747fe7>] ? schedule+0x9/0x1e
 [<ffffffff802c32a0>] ? bdi_sched_wait+0x9/0xd
 [<ffffffff807485ae>] ? __wait_on_bit+0x41/0x71
 [<ffffffff802c3297>] ? bdi_sched_wait+0x0/0xd
 [<ffffffff80748649>] ? out_of_line_wait_on_bit+0x6b/0x77
 [<ffffffff8024cc0c>] ? wake_bit_function+0x0/0x23
 [<ffffffff802c2f50>] ? bdi_writeback_all+0x134/0x16b
 [<ffffffff802c30ba>] ? generic_sync_sb_inodes+0x31/0xdc
 [<ffffffff802c31e8>] ? sync_inodes_sb+0x83/0x88
 [<ffffffff802c3233>] ? __sync_inodes+0x46/0x8f
 [<ffffffff802c5dac>] ? do_sync+0x36/0x5a
 [<ffffffff802c5df2>] ? sys_sync+0xe/0x14
 [<ffffffff8020ba2b>] ? system_call_fastpath+0x16/0x1b

> 
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 5a1837f..4a6859e 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -409,7 +409,7 @@ static struct bdi_work *get_next_work_item(struct backing_dev_info *bdi,
>  /*
>   * Retrieve work items and do the writeback they describe
>   */
> -static long wb_writeback(struct bdi_writeback *wb)
> +static long wb_writeback(struct bdi_writeback *wb, int force_wait)
>  {
>  	struct backing_dev_info *bdi = wb->bdi;
>  	struct bdi_work *work;
> @@ -418,7 +418,12 @@ static long wb_writeback(struct bdi_writeback *wb)
>  	while ((work = get_next_work_item(bdi, wb)) != NULL) {
>  		struct super_block *sb = bdi_work_sb(work);
>  		long nr_pages = work->nr_pages;
> -		enum writeback_sync_modes sync_mode = work->sync_mode;
> +		enum writeback_sync_modes sync_mode;
> +
> +		if (force_wait)
> +			sync_mode = WB_SYNC_ALL;
> +		else
> +			sync_mode = work->sync_mode;
>  
>  		/*
>  		 * If this isn't a data integrity operation, just notify
> @@ -444,7 +449,7 @@ static long wb_writeback(struct bdi_writeback *wb)
>   * This will be inlined in bdi_writeback_task() once we get rid of any
>   * dirty inodes on the default_backing_dev_info
>   */
> -long wb_do_writeback(struct bdi_writeback *wb)
> +long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
>  {
>  	long wrote;
>  
> @@ -461,7 +466,7 @@ long wb_do_writeback(struct bdi_writeback *wb)
>  	if (list_empty(&wb->bdi->work_list))
>  		wrote = wb_kupdated(wb);
>  	else
> -		wrote = wb_writeback(wb);
> +		wrote = wb_writeback(wb, force_wait);
>  
>  	return wrote;
>  }
> @@ -477,7 +482,7 @@ int bdi_writeback_task(struct bdi_writeback *wb)
>  	long pages_written;
>  
>  	while (!kthread_should_stop()) {
> -		pages_written = wb_do_writeback(wb);
> +		pages_written = wb_do_writeback(wb, 0);
>  
>  		if (pages_written)
>  			last_active = jiffies;
> diff --git a/include/linux/writeback.h b/include/linux/writeback.h
> index 0d4e31d..e070b91 100644
> --- a/include/linux/writeback.h
> +++ b/include/linux/writeback.h
> @@ -68,7 +68,7 @@ struct writeback_control {
>  void writeback_inodes(struct writeback_control *wbc);
>  int inode_wait(void *);
>  void sync_inodes_sb(struct super_block *, int wait);
> -long wb_do_writeback(struct bdi_writeback *wb);
> +long wb_do_writeback(struct bdi_writeback *wb, int force_wait);
>  
>  /* writeback.h requires fs.h; it, too, is not included from here. */
>  static inline void wait_on_inode(struct inode *inode)
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index 23013d5..0c91add 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -389,7 +389,7 @@ static int bdi_start_fn(void *ptr)
>  	 * will be added, since this bdi isn't discoverable anymore.
>  	 */
>  	if (!list_empty(&bdi->work_list))
> -		wb_do_writeback(wb);
> +		wb_do_writeback(wb, 1);
>  
>  	bdi_put_wb(bdi, wb);
>  	return ret;
> @@ -484,7 +484,7 @@ static int bdi_forker_task(void *ptr)
>  		 * dirty data on the default backing_dev_info
>  		 */
>  		if (wb_has_dirty_io(me) || !list_empty(&me->bdi->work_list))
> -			wb_do_writeback(me);
> +			wb_do_writeback(me, 0);
>  
>  		spin_lock(&bdi_lock);
>  
> 

Re: [PATCH 0/15] Per-bdi writeback flusher threads v10

[Jens Axboe]

On Thu, Jun 18 2009, Zhang, Yanmin wrote:
> On Tue, 2009-06-16 at 21:53 +0200, Jens Axboe wrote:
> > On Tue, Jun 16 2009, Jens Axboe wrote:
> > > On Tue, Jun 16 2009, Zhang, Yanmin wrote:
> > > > On Fri, 2009-06-12 at 14:54 +0200, Jens Axboe wrote:
> > > > > Hi,
> > > > > 
> > > > > Here's the 10th version of the writeback patches. Changes since v9:
> > > > > 
> > > > > - Fix bdi task exit race leaving work on the list, flush it after we
> > > > >   know we cannot be found anymore.
> > > > > - Rename flusher tasks from bdi-foo to flush-foo. Should make it more
> > > > >   clear to the casual observer.
> > > > > - Fix a problem with the btrfs bdi register patch that would spew
> > > > >   warnings for > 1 mounted btrfs file system.
> > > > > - Rebase to current -git, there were some conflicts with the latest work
> > > > >   from viro/hch.
> > > > > - Fix a block layer core problem were stacked devices would overwrite
> > > > >   the bdi state, causing problems and warning spew.
> > > > > - In bdi_writeback_all(), in the race occurence of a work allocation
> > > > >   failure, restart scanning from the beginning. Then we can drop the
> > > > >   bdi_lock mutex before diving into bdi specific writeback.
> > > > > - Convert bdi_lock to a spinlock.
> > > > > - Use spin_trylock() in bdi_writeback_all(), if this isn't a data
> > > > >   integrity writeback. Debatable, I kind of like it...
> > > > > - Get rid of BDI_CAP_FLUSH_FORKER, just check for match with the
> > > > >   default_backing_dev_info.
> > > > > - Fix race in list checking in bdi_forker_task().
> > > > > 
> > > > > 
> > > > > For ease of patching, I've put the full diff here:
> > > > > 
> > > > >   http://kernel.dk/writeback-v10.patch
> > > > Jens,
> > > > 
> > > > I applied the patch to 2.6.30 and got a confliction. The attachment is
> > > > the patch I ported to 2.6.30. Did I miss anything?
> > > > 
> > > > 
> > > > With the patch, kernel reports below messages on 2 machines.
> > > > 
> > > > INFO: task sync:29984 blocked for more than 120 seconds.
> > > > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > > > sync          D ffff88002805e300  6168 29984  24581
> > > >  ffff88022f84b780 0000000000000082 7fffffffffffffff ffff880133dbfe70
> > > >  0000000000000000 ffff88022e2b4c50 ffff88022e2b4fd8 00000001000c7bb8
> > > >  ffff88022f513fd0 ffff880133dbfde8 ffff880133dbfec8 ffff88022d5d13c8
> > > > Call Trace:
> > > >  [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
> > > >  [<ffffffff80780fde>] ? schedule+0x9/0x1d
> > > >  [<ffffffff802b69ed>] ? bdi_sched_wait+0x9/0xd
> > > >  [<ffffffff8078158d>] ? __wait_on_bit+0x40/0x6f
> > > >  [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
> > > >  [<ffffffff80781628>] ? out_of_line_wait_on_bit+0x6c/0x78
> > > >  [<ffffffff8024a426>] ? wake_bit_function+0x0/0x23
> > > >  [<ffffffff802b67ac>] ? bdi_writeback_all+0x12a/0x152
> > > >  [<ffffffff802b6805>] ? generic_sync_sb_inodes+0x31/0xde
> > > >  [<ffffffff802b6935>] ? sync_inodes_sb+0x83/0x88
> > > >  [<ffffffff802b6980>] ? __sync_inodes+0x46/0x8f
> > > >  [<ffffffff802b94f2>] ? do_sync+0x36/0x5a
> > > >  [<ffffffff802b9538>] ? sys_sync+0xe/0x12
> > > >  [<ffffffff8020b9ab>] ? system_call_fastpath+0x16/0x1b
> > > 
> > > I don't think it is your backport, for some reason the v10 missed a
> > > change that I think could solve this race. If not, there's another in
> > > there that I need to look at.
> > > 
> > > So against your current base, could you try with the below added as
> > > well? The printk() is just so we can see if this triggers for you or
> > > not.
> > 
> > OK that wont work, since we need to actually wait for the work to be
> > flushed, otherwise we wreak things when we free the bdi immediately
> > after that.
> > 
> > Can you try with this patch?
> Jens,
> 
> I tested below patch on 4 machines (run all fio sub-test cases twice which
> need more than 10 hours). The previous 2 machines don't stop this time.
> Unfortunately, the 3rd machine stops. I double-check the disassembled codes
> of kernel and make sure bdi_start_fn really calls wb_do_writeback.

Sorry I should have made that more clear when posting v11. This patch
wont fully solve the problem, however the v11 patch series should. So if
you test with that, hopefully all soft hangs should be gone.

-- 
Jens Axboe

Re: [PATCH 0/15] Per-bdi writeback flusher threads v10

[Zhang, Yanmin]

On Thu, 2009-06-18 at 07:13 +0200, Jens Axboe wrote:
> On Thu, Jun 18 2009, Zhang, Yanmin wrote:
> > On Tue, 2009-06-16 at 21:53 +0200, Jens Axboe wrote:
> > > On Tue, Jun 16 2009, Jens Axboe wrote:
> > > > On Tue, Jun 16 2009, Zhang, Yanmin wrote:
> > > > > On Fri, 2009-06-12 at 14:54 +0200, Jens Axboe wrote:
> > > > > > Hi,
> > > > > > 
> > > > > > Here's the 10th version of the writeback patches. Changes since v9:
> > > > > > 
> > > > > > - Fix bdi task exit race leaving work on the list, flush it after we
> > > > > >   know we cannot be found anymore.
> > > > > > - Rename flusher tasks from bdi-foo to flush-foo. Should make it more
> > > > > >   clear to the casual observer.
> > > > > > - Fix a problem with the btrfs bdi register patch that would spew
> > > > > >   warnings for > 1 mounted btrfs file system.
> > > > > > - Rebase to current -git, there were some conflicts with the latest work
> > > > > >   from viro/hch.
> > > > > > - Fix a block layer core problem were stacked devices would overwrite
> > > > > >   the bdi state, causing problems and warning spew.
> > > > > > - In bdi_writeback_all(), in the race occurence of a work allocation
> > > > > >   failure, restart scanning from the beginning. Then we can drop the
> > > > > >   bdi_lock mutex before diving into bdi specific writeback.
> > > > > > - Convert bdi_lock to a spinlock.
> > > > > > - Use spin_trylock() in bdi_writeback_all(), if this isn't a data
> > > > > >   integrity writeback. Debatable, I kind of like it...
> > > > > > - Get rid of BDI_CAP_FLUSH_FORKER, just check for match with the
> > > > > >   default_backing_dev_info.
> > > > > > - Fix race in list checking in bdi_forker_task().
> > > > > > 
> > > > > > 
> > > > > > For ease of patching, I've put the full diff here:
> > > > > > 
> > > > > >   http://kernel.dk/writeback-v10.patch
> > > > > Jens,
> > > > > 
> > > > > I applied the patch to 2.6.30 and got a confliction. The attachment is
> > > > > the patch I ported to 2.6.30. Did I miss anything?
> > > > > 
> > > > > 
> > > > > With the patch, kernel reports below messages on 2 machines.
> > > > > 
> > > > > INFO: task sync:29984 blocked for more than 120 seconds.
> > > > > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > > > > sync          D ffff88002805e300  6168 29984  24581
> > > > >  ffff88022f84b780 0000000000000082 7fffffffffffffff ffff880133dbfe70
> > > > >  0000000000000000 ffff88022e2b4c50 ffff88022e2b4fd8 00000001000c7bb8
> > > > >  ffff88022f513fd0 ffff880133dbfde8 ffff880133dbfec8 ffff88022d5d13c8
> > > > > Call Trace:
> > > > >  [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
> > > > >  [<ffffffff80780fde>] ? schedule+0x9/0x1d
> > > > >  [<ffffffff802b69ed>] ? bdi_sched_wait+0x9/0xd
> > > > >  [<ffffffff8078158d>] ? __wait_on_bit+0x40/0x6f
> > > > >  [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
> > > > >  [<ffffffff80781628>] ? out_of_line_wait_on_bit+0x6c/0x78
> > > > >  [<ffffffff8024a426>] ? wake_bit_function+0x0/0x23
> > > > >  [<ffffffff802b67ac>] ? bdi_writeback_all+0x12a/0x152
> > > > >  [<ffffffff802b6805>] ? generic_sync_sb_inodes+0x31/0xde
> > > > >  [<ffffffff802b6935>] ? sync_inodes_sb+0x83/0x88
> > > > >  [<ffffffff802b6980>] ? __sync_inodes+0x46/0x8f
> > > > >  [<ffffffff802b94f2>] ? do_sync+0x36/0x5a
> > > > >  [<ffffffff802b9538>] ? sys_sync+0xe/0x12
> > > > >  [<ffffffff8020b9ab>] ? system_call_fastpath+0x16/0x1b
> > > > 
> > > > I don't think it is your backport, for some reason the v10 missed a
> > > > change that I think could solve this race. If not, there's another in
> > > > there that I need to look at.
> > > > 
> > > > So against your current base, could you try with the below added as
> > > > well? The printk() is just so we can see if this triggers for you or
> > > > not.
> > > 
> > > OK that wont work, since we need to actually wait for the work to be
> > > flushed, otherwise we wreak things when we free the bdi immediately
> > > after that.
> > > 
> > > Can you try with this patch?
> > Jens,
> > 
> > I tested below patch on 4 machines (run all fio sub-test cases twice which
> > need more than 10 hours). The previous 2 machines don't stop this time.
> > Unfortunately, the 3rd machine stops. I double-check the disassembled codes
> > of kernel and make sure bdi_start_fn really calls wb_do_writeback.
> 
> Sorry I should have made that more clear when posting v11. This patch
> wont fully solve the problem, however the v11 patch series should. So if
> you test with that, hopefully all soft hangs should be gone.
Ok. I will start new testing against V11. I also add some debugging codes into
V11.

Re: [PATCH 0/15] Per-bdi writeback flusher threads v10

[Jens Axboe]

On Thu, Jun 18 2009, Zhang, Yanmin wrote:
> On Thu, 2009-06-18 at 07:13 +0200, Jens Axboe wrote:
> > On Thu, Jun 18 2009, Zhang, Yanmin wrote:
> > > On Tue, 2009-06-16 at 21:53 +0200, Jens Axboe wrote:
> > > > On Tue, Jun 16 2009, Jens Axboe wrote:
> > > > > On Tue, Jun 16 2009, Zhang, Yanmin wrote:
> > > > > > On Fri, 2009-06-12 at 14:54 +0200, Jens Axboe wrote:
> > > > > > > Hi,
> > > > > > > 
> > > > > > > Here's the 10th version of the writeback patches. Changes since v9:
> > > > > > > 
> > > > > > > - Fix bdi task exit race leaving work on the list, flush it after we
> > > > > > >   know we cannot be found anymore.
> > > > > > > - Rename flusher tasks from bdi-foo to flush-foo. Should make it more
> > > > > > >   clear to the casual observer.
> > > > > > > - Fix a problem with the btrfs bdi register patch that would spew
> > > > > > >   warnings for > 1 mounted btrfs file system.
> > > > > > > - Rebase to current -git, there were some conflicts with the latest work
> > > > > > >   from viro/hch.
> > > > > > > - Fix a block layer core problem were stacked devices would overwrite
> > > > > > >   the bdi state, causing problems and warning spew.
> > > > > > > - In bdi_writeback_all(), in the race occurence of a work allocation
> > > > > > >   failure, restart scanning from the beginning. Then we can drop the
> > > > > > >   bdi_lock mutex before diving into bdi specific writeback.
> > > > > > > - Convert bdi_lock to a spinlock.
> > > > > > > - Use spin_trylock() in bdi_writeback_all(), if this isn't a data
> > > > > > >   integrity writeback. Debatable, I kind of like it...
> > > > > > > - Get rid of BDI_CAP_FLUSH_FORKER, just check for match with the
> > > > > > >   default_backing_dev_info.
> > > > > > > - Fix race in list checking in bdi_forker_task().
> > > > > > > 
> > > > > > > 
> > > > > > > For ease of patching, I've put the full diff here:
> > > > > > > 
> > > > > > >   http://kernel.dk/writeback-v10.patch
> > > > > > Jens,
> > > > > > 
> > > > > > I applied the patch to 2.6.30 and got a confliction. The attachment is
> > > > > > the patch I ported to 2.6.30. Did I miss anything?
> > > > > > 
> > > > > > 
> > > > > > With the patch, kernel reports below messages on 2 machines.
> > > > > > 
> > > > > > INFO: task sync:29984 blocked for more than 120 seconds.
> > > > > > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > > > > > sync          D ffff88002805e300  6168 29984  24581
> > > > > >  ffff88022f84b780 0000000000000082 7fffffffffffffff ffff880133dbfe70
> > > > > >  0000000000000000 ffff88022e2b4c50 ffff88022e2b4fd8 00000001000c7bb8
> > > > > >  ffff88022f513fd0 ffff880133dbfde8 ffff880133dbfec8 ffff88022d5d13c8
> > > > > > Call Trace:
> > > > > >  [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
> > > > > >  [<ffffffff80780fde>] ? schedule+0x9/0x1d
> > > > > >  [<ffffffff802b69ed>] ? bdi_sched_wait+0x9/0xd
> > > > > >  [<ffffffff8078158d>] ? __wait_on_bit+0x40/0x6f
> > > > > >  [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
> > > > > >  [<ffffffff80781628>] ? out_of_line_wait_on_bit+0x6c/0x78
> > > > > >  [<ffffffff8024a426>] ? wake_bit_function+0x0/0x23
> > > > > >  [<ffffffff802b67ac>] ? bdi_writeback_all+0x12a/0x152
> > > > > >  [<ffffffff802b6805>] ? generic_sync_sb_inodes+0x31/0xde
> > > > > >  [<ffffffff802b6935>] ? sync_inodes_sb+0x83/0x88
> > > > > >  [<ffffffff802b6980>] ? __sync_inodes+0x46/0x8f
> > > > > >  [<ffffffff802b94f2>] ? do_sync+0x36/0x5a
> > > > > >  [<ffffffff802b9538>] ? sys_sync+0xe/0x12
> > > > > >  [<ffffffff8020b9ab>] ? system_call_fastpath+0x16/0x1b
> > > > > 
> > > > > I don't think it is your backport, for some reason the v10 missed a
> > > > > change that I think could solve this race. If not, there's another in
> > > > > there that I need to look at.
> > > > > 
> > > > > So against your current base, could you try with the below added as
> > > > > well? The printk() is just so we can see if this triggers for you or
> > > > > not.
> > > > 
> > > > OK that wont work, since we need to actually wait for the work to be
> > > > flushed, otherwise we wreak things when we free the bdi immediately
> > > > after that.
> > > > 
> > > > Can you try with this patch?
> > > Jens,
> > > 
> > > I tested below patch on 4 machines (run all fio sub-test cases twice which
> > > need more than 10 hours). The previous 2 machines don't stop this time.
> > > Unfortunately, the 3rd machine stops. I double-check the disassembled codes
> > > of kernel and make sure bdi_start_fn really calls wb_do_writeback.
> > 
> > Sorry I should have made that more clear when posting v11. This patch
> > wont fully solve the problem, however the v11 patch series should. So if
> > you test with that, hopefully all soft hangs should be gone.
> Ok. I will start new testing against V11. I also add some debugging codes into
> V11.

Great, thanks! There's a small issue with v11 that you should be aware
of. The test for bdi_add_default_flusher_task() was inverted. I'm
attaching a diff at the end. The interesting bit is the 2nd hunk of
backing-dev.c, the others are just a cleanup.

diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 6815f8b..e623c57 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -107,7 +107,6 @@ void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
 			 long nr_pages, enum writeback_sync_modes sync_mode);
 int bdi_writeback_task(struct bdi_writeback *wb);
 void bdi_writeback_all(struct super_block *sb, struct writeback_control *wbc);
-void bdi_add_default_flusher_task(struct backing_dev_info *bdi);
 void bdi_add_flusher_task(struct backing_dev_info *bdi);
 int bdi_has_dirty_io(struct backing_dev_info *bdi);
 
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index b4517ee..c2eec72 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -37,6 +37,8 @@ static int bdi_sync_supers(void *);
 static void sync_supers_timer_fn(unsigned long);
 static void arm_supers_timer(void);
 
+static void bdi_add_default_flusher_task(struct backing_dev_info *bdi);
+
 #ifdef CONFIG_DEBUG_FS
 #include <linux/debugfs.h>
 #include <linux/seq_file.h>
@@ -496,7 +498,7 @@ static int bdi_forker_task(void *ptr)
 		list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
 			if (bdi->wb.task)
 				continue;
-			if (!list_empty(&bdi->work_list) &&
+			if (list_empty(&bdi->work_list) &&
 			    !bdi_has_dirty_io(bdi))
 				continue;
 
@@ -607,7 +609,7 @@ static int flusher_add_helper_test(struct backing_dev_info *bdi)
  * Add the default flusher task that gets created for any bdi
  * that has dirty data pending writeout
  */
-void bdi_add_default_flusher_task(struct backing_dev_info *bdi)
+void static bdi_add_default_flusher_task(struct backing_dev_info *bdi)
 {
 	bdi_add_one_flusher_task(bdi, flusher_add_helper_test);
 }

-- 
Jens Axboe

Re: [PATCH 0/15] Per-bdi writeback flusher threads v10

[Zhang, Yanmin]

On Thu, 2009-06-18 at 14:35 +0200, Jens Axboe wrote:
> On Thu, Jun 18 2009, Zhang, Yanmin wrote:
> > On Thu, 2009-06-18 at 07:13 +0200, Jens Axboe wrote:
> > > On Thu, Jun 18 2009, Zhang, Yanmin wrote:
> > > > On Tue, 2009-06-16 at 21:53 +0200, Jens Axboe wrote:
> > > > > On Tue, Jun 16 2009, Jens Axboe wrote:
> > > > > > On Tue, Jun 16 2009, Zhang, Yanmin wrote:
> > > > > > > On Fri, 2009-06-12 at 14:54 +0200, Jens Axboe wrote:
> > > > > > > > Hi,
> > > > > > > > 
> > > > > > > > Here's the 10th version of the writeback patches. Changes since v9:
> > > > > > > > 
> > > > > > > > - Fix bdi task exit race leaving work on the list, flush it after we
> > > > > > > >   know we cannot be found anymore.
> > > > > > > > - Rename flusher tasks from bdi-foo to flush-foo. Should make it more
> > > > > > > >   clear to the casual observer.
> > > > > > > > - Fix a problem with the btrfs bdi register patch that would spew
> > > > > > > >   warnings for > 1 mounted btrfs file system.
> > > > > > > > - Rebase to current -git, there were some conflicts with the latest work
> > > > > > > >   from viro/hch.
> > > > > > > > - Fix a block layer core problem were stacked devices would overwrite
> > > > > > > >   the bdi state, causing problems and warning spew.
> > > > > > > > - In bdi_writeback_all(), in the race occurence of a work allocation
> > > > > > > >   failure, restart scanning from the beginning. Then we can drop the
> > > > > > > >   bdi_lock mutex before diving into bdi specific writeback.
> > > > > > > > - Convert bdi_lock to a spinlock.
> > > > > > > > - Use spin_trylock() in bdi_writeback_all(), if this isn't a data
> > > > > > > >   integrity writeback. Debatable, I kind of like it...
> > > > > > > > - Get rid of BDI_CAP_FLUSH_FORKER, just check for match with the
> > > > > > > >   default_backing_dev_info.
> > > > > > > > - Fix race in list checking in bdi_forker_task().
> > > > > > > > 
> > > > > > > > 
> > > > > > > > For ease of patching, I've put the full diff here:
> > > > > > > > 
> > > > > > > >   http://kernel.dk/writeback-v10.patch
> > > > > > > Jens,
> > > > > > > 
> > > > > > > I applied the patch to 2.6.30 and got a confliction. The attachment is
> > > > > > > the patch I ported to 2.6.30. Did I miss anything?
> > > > > > > 
> > > > > > > 
> > > > > > > With the patch, kernel reports below messages on 2 machines.
> > > > > > > 
> > > > > > > INFO: task sync:29984 blocked for more than 120 seconds.
> > > > > > > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > > > > > > sync          D ffff88002805e300  6168 29984  24581
> > > > > > >  ffff88022f84b780 0000000000000082 7fffffffffffffff ffff880133dbfe70
> > > > > > >  0000000000000000 ffff88022e2b4c50 ffff88022e2b4fd8 00000001000c7bb8
> > > > > > >  ffff88022f513fd0 ffff880133dbfde8 ffff880133dbfec8 ffff88022d5d13c8
> > > > > > > Call Trace:
> > > > > > >  [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
> > > > > > >  [<ffffffff80780fde>] ? schedule+0x9/0x1d
> > > > > > >  [<ffffffff802b69ed>] ? bdi_sched_wait+0x9/0xd
> > > > > > >  [<ffffffff8078158d>] ? __wait_on_bit+0x40/0x6f
> > > > > > >  [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
> > > > > > >  [<ffffffff80781628>] ? out_of_line_wait_on_bit+0x6c/0x78
> > > > > > >  [<ffffffff8024a426>] ? wake_bit_function+0x0/0x23
> > > > > > >  [<ffffffff802b67ac>] ? bdi_writeback_all+0x12a/0x152
> > > > > > >  [<ffffffff802b6805>] ? generic_sync_sb_inodes+0x31/0xde
> > > > > > >  [<ffffffff802b6935>] ? sync_inodes_sb+0x83/0x88
> > > > > > >  [<ffffffff802b6980>] ? __sync_inodes+0x46/0x8f
> > > > > > >  [<ffffffff802b94f2>] ? do_sync+0x36/0x5a
> > > > > > >  [<ffffffff802b9538>] ? sys_sync+0xe/0x12
> > > > > > >  [<ffffffff8020b9ab>] ? system_call_fastpath+0x16/0x1b
> > > > > > 
> > > > > > I don't think it is your backport, for some reason the v10 missed a
> > > > > > change that I think could solve this race. If not, there's another in
> > > > > > there that I need to look at.
> > > > > > 
> > > > > > So against your current base, could you try with the below added as
> > > > > > well? The printk() is just so we can see if this triggers for you or
> > > > > > not.
> > > > > 
> > > > > OK that wont work, since we need to actually wait for the work to be
> > > > > flushed, otherwise we wreak things when we free the bdi immediately
> > > > > after that.
> > > > > 
> > > > > Can you try with this patch?
> > > > Jens,
> > > > 
> > > > I tested below patch on 4 machines (run all fio sub-test cases twice which
> > > > need more than 10 hours). The previous 2 machines don't stop this time.
> > > > Unfortunately, the 3rd machine stops. I double-check the disassembled codes
> > > > of kernel and make sure bdi_start_fn really calls wb_do_writeback.
> > > 
> > > Sorry I should have made that more clear when posting v11. This patch
> > > wont fully solve the problem, however the v11 patch series should. So if
> > > you test with that, hopefully all soft hangs should be gone.
> > Ok. I will start new testing against V11. I also add some debugging codes into
> > V11.
> 
> Great, thanks! There's a small issue with v11 that you should be aware
> of. The test for bdi_add_default_flusher_task() was inverted. I'm
> attaching a diff at the end. The interesting bit is the 2nd hunk of
> backing-dev.c, the others are just a cleanup.
Jens,

I did entensive testing with fio (especially the aio randread which triggers
the hang)/ffsb and a couple of other testing and didn't hit the hang issue.
So V11 does fix the issue.

>From performance point of view, there is no big difference than old versions.

Yanmin

> 
> diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
> index 6815f8b..e623c57 100644
> --- a/include/linux/backing-dev.h
> +++ b/include/linux/backing-dev.h
> @@ -107,7 +107,6 @@ void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
>  			 long nr_pages, enum writeback_sync_modes sync_mode);
>  int bdi_writeback_task(struct bdi_writeback *wb);
>  void bdi_writeback_all(struct super_block *sb, struct writeback_control *wbc);
> -void bdi_add_default_flusher_task(struct backing_dev_info *bdi);
>  void bdi_add_flusher_task(struct backing_dev_info *bdi);
>  int bdi_has_dirty_io(struct backing_dev_info *bdi);
>  
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index b4517ee..c2eec72 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -37,6 +37,8 @@ static int bdi_sync_supers(void *);
>  static void sync_supers_timer_fn(unsigned long);
>  static void arm_supers_timer(void);
>  
> +static void bdi_add_default_flusher_task(struct backing_dev_info *bdi);
> +
>  #ifdef CONFIG_DEBUG_FS
>  #include <linux/debugfs.h>
>  #include <linux/seq_file.h>
> @@ -496,7 +498,7 @@ static int bdi_forker_task(void *ptr)
>  		list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
>  			if (bdi->wb.task)
>  				continue;
> -			if (!list_empty(&bdi->work_list) &&
> +			if (list_empty(&bdi->work_list) &&
>  			    !bdi_has_dirty_io(bdi))
>  				continue;
>  
> @@ -607,7 +609,7 @@ static int flusher_add_helper_test(struct backing_dev_info *bdi)
>   * Add the default flusher task that gets created for any bdi
>   * that has dirty data pending writeout
>   */
> -void bdi_add_default_flusher_task(struct backing_dev_info *bdi)
> +void static bdi_add_default_flusher_task(struct backing_dev_info *bdi)
>  {
>  	bdi_add_one_flusher_task(bdi, flusher_add_helper_test);
>  }
> 

Re: [PATCH 0/15] Per-bdi writeback flusher threads v10

[Jens Axboe]

On Fri, Jun 19 2009, Zhang, Yanmin wrote:
> > > > Sorry I should have made that more clear when posting v11. This patch
> > > > wont fully solve the problem, however the v11 patch series should. So if
> > > > you test with that, hopefully all soft hangs should be gone.
> > > Ok. I will start new testing against V11. I also add some debugging codes into
> > > V11.
> > 
> > Great, thanks! There's a small issue with v11 that you should be aware
> > of. The test for bdi_add_default_flusher_task() was inverted. I'm
> > attaching a diff at the end. The interesting bit is the 2nd hunk of
> > backing-dev.c, the others are just a cleanup.
> Jens,
> 
> I did entensive testing with fio (especially the aio randread which triggers
> the hang)/ffsb and a couple of other testing and didn't hit the hang issue.
> So V11 does fix the issue.

Great!

> From performance point of view, there is no big difference than old versions.

That's fine too, it's only been bug fixes the last few revisions. I'll
tag a v12 with the small fix.

-- 
Jens Axboe

Re: [PATCH 0/15] Per-bdi writeback flusher threads v10

[Zhang, Yanmin]

On Tue, 2009-06-16 at 10:00 +0200, Jens Axboe wrote:
> On Tue, Jun 16 2009, Zhang, Yanmin wrote:
> > On Fri, 2009-06-12 at 14:54 +0200, Jens Axboe wrote:
> > > Hi,
> > > 
> > > Here's the 10th version of the writeback patches. Changes since v9:
> > > 
> > > - Fix bdi task exit race leaving work on the list, flush it after we
> > >   know we cannot be found anymore.
> > > - Rename flusher tasks from bdi-foo to flush-foo. Should make it more
> > >   clear to the casual observer.
> > > - Fix a problem with the btrfs bdi register patch that would spew
> > >   warnings for > 1 mounted btrfs file system.
> > > - Rebase to current -git, there were some conflicts with the latest work
> > >   from viro/hch.
> > > - Fix a block layer core problem were stacked devices would overwrite
> > >   the bdi state, causing problems and warning spew.
> > > - In bdi_writeback_all(), in the race occurence of a work allocation
> > >   failure, restart scanning from the beginning. Then we can drop the
> > >   bdi_lock mutex before diving into bdi specific writeback.
> > > - Convert bdi_lock to a spinlock.
> > > - Use spin_trylock() in bdi_writeback_all(), if this isn't a data
> > >   integrity writeback. Debatable, I kind of like it...
> > > - Get rid of BDI_CAP_FLUSH_FORKER, just check for match with the
> > >   default_backing_dev_info.
> > > - Fix race in list checking in bdi_forker_task().
> > > 
> > > 
> > > For ease of patching, I've put the full diff here:
> > > 
> > >   http://kernel.dk/writeback-v10.patch
> > Jens,
> > 
> > I applied the patch to 2.6.30 and got a confliction. The attachment is
> > the patch I ported to 2.6.30. Did I miss anything?
> > 
> > 
> > With the patch, kernel reports below messages on 2 machines.
> > 
> > INFO: task sync:29984 blocked for more than 120 seconds.
> > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > sync          D ffff88002805e300  6168 29984  24581
> >  ffff88022f84b780 0000000000000082 7fffffffffffffff ffff880133dbfe70
> >  0000000000000000 ffff88022e2b4c50 ffff88022e2b4fd8 00000001000c7bb8
> >  ffff88022f513fd0 ffff880133dbfde8 ffff880133dbfec8 ffff88022d5d13c8
> > Call Trace:
> >  [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
> >  [<ffffffff80780fde>] ? schedule+0x9/0x1d
> >  [<ffffffff802b69ed>] ? bdi_sched_wait+0x9/0xd
> >  [<ffffffff8078158d>] ? __wait_on_bit+0x40/0x6f
> >  [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
> >  [<ffffffff80781628>] ? out_of_line_wait_on_bit+0x6c/0x78
> >  [<ffffffff8024a426>] ? wake_bit_function+0x0/0x23
> >  [<ffffffff802b67ac>] ? bdi_writeback_all+0x12a/0x152
> >  [<ffffffff802b6805>] ? generic_sync_sb_inodes+0x31/0xde
> >  [<ffffffff802b6935>] ? sync_inodes_sb+0x83/0x88
> >  [<ffffffff802b6980>] ? __sync_inodes+0x46/0x8f
> >  [<ffffffff802b94f2>] ? do_sync+0x36/0x5a
> >  [<ffffffff802b9538>] ? sys_sync+0xe/0x12
> >  [<ffffffff8020b9ab>] ? system_call_fastpath+0x16/0x1b
> 
> I don't think it is your backport, for some reason the v10 missed a
> change that I think could solve this race. If not, there's another in
> there that I need to look at.
> 
> So against your current base, could you try with the below added as
> well? The printk() is just so we can see if this triggers for you or
> not.
> 
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index b3e80c5..a065da5 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -384,6 +384,15 @@ static int bdi_start_fn(void *ptr)
>  	 */
>  	synchronize_srcu(&bdi->srcu);
>  
> +	/*
> +	 * Flush any pending work. No more can be added, since
> +	 * the bdi is no longer discoverable.
> +	 */
> +	if (!list_empty(&bdi->work_list)) {
> +		printk("bdi: flushing racy work\n");
I ran testings with the patch. 2 machines reported the same issues when do sync
just after mounting filesystems for testing.

These 2 machines did print out above info. One printed it just before dumping the
blocking info.

I ran a series of test cases. Every case does umount filesystems, then mount
them again for testing.

> +		wb_do_writeback(wb);
> +	}
> +
>  	bdi_put_wb(bdi, wb);
>  	return ret;
>  }
> 

Re: [PATCH 0/15] Per-bdi writeback flusher threads v10

[Jens Axboe]

On Wed, Jun 17 2009, Zhang, Yanmin wrote:
> On Tue, 2009-06-16 at 10:00 +0200, Jens Axboe wrote:
> > On Tue, Jun 16 2009, Zhang, Yanmin wrote:
> > > On Fri, 2009-06-12 at 14:54 +0200, Jens Axboe wrote:
> > > > Hi,
> > > > 
> > > > Here's the 10th version of the writeback patches. Changes since v9:
> > > > 
> > > > - Fix bdi task exit race leaving work on the list, flush it after we
> > > >   know we cannot be found anymore.
> > > > - Rename flusher tasks from bdi-foo to flush-foo. Should make it more
> > > >   clear to the casual observer.
> > > > - Fix a problem with the btrfs bdi register patch that would spew
> > > >   warnings for > 1 mounted btrfs file system.
> > > > - Rebase to current -git, there were some conflicts with the latest work
> > > >   from viro/hch.
> > > > - Fix a block layer core problem were stacked devices would overwrite
> > > >   the bdi state, causing problems and warning spew.
> > > > - In bdi_writeback_all(), in the race occurence of a work allocation
> > > >   failure, restart scanning from the beginning. Then we can drop the
> > > >   bdi_lock mutex before diving into bdi specific writeback.
> > > > - Convert bdi_lock to a spinlock.
> > > > - Use spin_trylock() in bdi_writeback_all(), if this isn't a data
> > > >   integrity writeback. Debatable, I kind of like it...
> > > > - Get rid of BDI_CAP_FLUSH_FORKER, just check for match with the
> > > >   default_backing_dev_info.
> > > > - Fix race in list checking in bdi_forker_task().
> > > > 
> > > > 
> > > > For ease of patching, I've put the full diff here:
> > > > 
> > > >   http://kernel.dk/writeback-v10.patch
> > > Jens,
> > > 
> > > I applied the patch to 2.6.30 and got a confliction. The attachment is
> > > the patch I ported to 2.6.30. Did I miss anything?
> > > 
> > > 
> > > With the patch, kernel reports below messages on 2 machines.
> > > 
> > > INFO: task sync:29984 blocked for more than 120 seconds.
> > > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > > sync          D ffff88002805e300  6168 29984  24581
> > >  ffff88022f84b780 0000000000000082 7fffffffffffffff ffff880133dbfe70
> > >  0000000000000000 ffff88022e2b4c50 ffff88022e2b4fd8 00000001000c7bb8
> > >  ffff88022f513fd0 ffff880133dbfde8 ffff880133dbfec8 ffff88022d5d13c8
> > > Call Trace:
> > >  [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
> > >  [<ffffffff80780fde>] ? schedule+0x9/0x1d
> > >  [<ffffffff802b69ed>] ? bdi_sched_wait+0x9/0xd
> > >  [<ffffffff8078158d>] ? __wait_on_bit+0x40/0x6f
> > >  [<ffffffff802b69e4>] ? bdi_sched_wait+0x0/0xd
> > >  [<ffffffff80781628>] ? out_of_line_wait_on_bit+0x6c/0x78
> > >  [<ffffffff8024a426>] ? wake_bit_function+0x0/0x23
> > >  [<ffffffff802b67ac>] ? bdi_writeback_all+0x12a/0x152
> > >  [<ffffffff802b6805>] ? generic_sync_sb_inodes+0x31/0xde
> > >  [<ffffffff802b6935>] ? sync_inodes_sb+0x83/0x88
> > >  [<ffffffff802b6980>] ? __sync_inodes+0x46/0x8f
> > >  [<ffffffff802b94f2>] ? do_sync+0x36/0x5a
> > >  [<ffffffff802b9538>] ? sys_sync+0xe/0x12
> > >  [<ffffffff8020b9ab>] ? system_call_fastpath+0x16/0x1b
> > 
> > I don't think it is your backport, for some reason the v10 missed a
> > change that I think could solve this race. If not, there's another in
> > there that I need to look at.
> > 
> > So against your current base, could you try with the below added as
> > well? The printk() is just so we can see if this triggers for you or
> > not.
> > 
> > diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> > index b3e80c5..a065da5 100644
> > --- a/mm/backing-dev.c
> > +++ b/mm/backing-dev.c
> > @@ -384,6 +384,15 @@ static int bdi_start_fn(void *ptr)
> >  	 */
> >  	synchronize_srcu(&bdi->srcu);
> >  
> > +	/*
> > +	 * Flush any pending work. No more can be added, since
> > +	 * the bdi is no longer discoverable.
> > +	 */
> > +	if (!list_empty(&bdi->work_list)) {
> > +		printk("bdi: flushing racy work\n");
> I ran testings with the patch. 2 machines reported the same issues
> when do sync just after mounting filesystems for testing.
> 
> These 2 machines did print out above info. One printed it just before
> dumping the blocking info.

Great, then I'm pretty confident that this is the issue. When if you
have, it help if you could try the 2nd patch and see if it resolves the
issue.

-- 
Jens Axboe