[PATCH 0/13] Per-bdi writeback flusher threads #3

[PATCH 0/13] Per-bdi writeback flusher threads #3

[Jens Axboe]

Hi,

This is the third version of the patchset. Changes since v2:

- Dropped some of the prep patches, since they are now in mainline.
  Unfortunately we grew another pdflush_operation() user (emergency thaw),
  so I had to introduce a new prep patch for that.

- Fix the data consistency issue in generic_sync_sb_inodes() with
  WB_SYNC_ALL that Jan Kara pointed out. I had to switch bdi_list
  to SRCU protection for this. I pondered using a mutex for bdi_lock,
  but that does not work with the pending list <-> active list
  RCU callback scheme.

- Fix race in bdi task removal, we need to synchronize_rcu() before
  doing the wb task kill, not after. This ensures that once we do the
  task kill, nobody is accessing our bdi anymore.

- Separate default wb task creation from filesystem initiated task
  additions. The former can be racy and should check the pending bit
  only to see whether it should proceed, the latter should block waiting
  for previous task additions to finish.

- Move the bdi_cap_flusher_forker() back in the series to where the
  BDI_CAP_FLUSH_FORKER flag was introduced.

- Fix a problem where the first incremental step ended up writing back
  all the dirty inodes on a bdi, not just the ones belonging to a
  specific super_block. Only a problem after the first patch, the 2nd
  patch in the series got it right again. (Thanks Jan Kara).

- Allow writeback tasks to exit, if the bdi has been idle for a certain
  period of time. The lazy create will recreate them if we see dirty
  inodes on the bdi later on.

- btrfs must register its fs_info bdi, or direct writeback will not work
  as intended. Also kill capabilities inherit from
  default_backing_dev_info and fix failure to check bdi_init() return
  value.

The branch can be pulled from:

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

Or these patches can be applied directly to 2.6.30-rc1.

-- 
Jens Axboe

[PATCH 01/13] buffer: switch do_emergency_thaw() away from pdflush_operation()

[Jens Axboe]

This is (again) a preparatory patch similar to commit
a2a9537ac0b37a5da6fbe7e1e9cb06c524d2a9c4. It open codes a simple
async way of executing do_thaw_all() out of context, so we can get
rid of pdflush.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 fs/buffer.c |   11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 6e35762..6a18802 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -547,7 +547,7 @@ repeat:
 	return err;
 }
 
-void do_thaw_all(unsigned long unused)
+void do_thaw_all(struct work_struct *work)
 {
 	struct super_block *sb;
 	char b[BDEVNAME_SIZE];
@@ -567,6 +567,7 @@ restart:
 			goto restart;
 	}
 	spin_unlock(&sb_lock);
+	kfree(work);
 	printk(KERN_WARNING "Emergency Thaw complete\n");
 }
 
@@ -577,7 +578,13 @@ restart:
  */
 void emergency_thaw_all(void)
 {
-	pdflush_operation(do_thaw_all, 0);
+	struct work_struct *work;
+
+	work = kmalloc(sizeof(*work), GFP_ATOMIC);
+	if (work) {
+		INIT_WORK(work, do_thaw_all);
+		schedule_work(work);
+	}
 }
 
 /**
-- 
1.6.2.2.446.gfbdc0

Re: [PATCH 01/13] buffer: switch do_emergency_thaw() away from pdflush_operation()

[Christoph Hellwig]

On Wed, Apr 08, 2009 at 02:00:04PM +0200, Jens Axboe wrote:
> This is (again) a preparatory patch similar to commit
> a2a9537ac0b37a5da6fbe7e1e9cb06c524d2a9c4. It open codes a simple
> async way of executing do_thaw_all() out of context, so we can get
> rid of pdflush.

Any good reason this isn't pushed upstream for 2.6.30 yet?

And if someone is inclined to clean up this area some generic way to
run sysrq tasks in user context would be great, as a lot of them need
to.

Re: [PATCH 01/13] buffer: switch do_emergency_thaw() away from pdflush_operation()

[Jens Axboe]

On Wed, Apr 08 2009, Christoph Hellwig wrote:
> On Wed, Apr 08, 2009 at 02:00:04PM +0200, Jens Axboe wrote:
> > This is (again) a preparatory patch similar to commit
> > a2a9537ac0b37a5da6fbe7e1e9cb06c524d2a9c4. It open codes a simple
> > async way of executing do_thaw_all() out of context, so we can get
> > rid of pdflush.
> 
> Any good reason this isn't pushed upstream for 2.6.30 yet?

The previous ones ARE in 2.6.30-rc1, but this one got added after 2.6.29
was released. I'll push this one, too.

> And if someone is inclined to clean up this area some generic way to
> run sysrq tasks in user context would be great, as a lot of them need
> to.

-- 
Jens Axboe

[PATCH 02/13] 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            |   30 +++++++
 mm/page-writeback.c         |    1 -
 6 files changed, 166 insertions(+), 78 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 91013ff..34c8d1d 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
@@ -158,12 +159,13 @@ 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:
@@ -184,31 +186,30 @@ 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)
@@ -255,18 +256,50 @@ 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
+	 */
+	rcu_read_lock();
+	list_for_each_entry_rcu(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;
+		}
+	}
+	rcu_read_unlock();
+
+	return ret;
 }
 EXPORT_SYMBOL(sb_has_dirty_inodes);
 
@@ -322,11 +355,11 @@ __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
@@ -336,7 +369,7 @@ __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;
@@ -402,10 +435,10 @@ __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;
@@ -428,51 +461,34 @@ __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
@@ -494,14 +510,14 @@ 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 */
@@ -539,13 +555,55 @@ 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;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
+		generic_sync_bdi_inodes(bdi, wbc, sb, is_blkdev_sb);
+	rcu_read_unlock();
+
+	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 +641,8 @@ 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);
 
@@ -601,8 +657,8 @@ 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 786fe7d..d438f27 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -64,9 +64,6 @@ 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..86668c7 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 spinlock_t 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 4d40b69..1f76516 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -636,7 +636,7 @@ 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;
@@ -1256,9 +1256,6 @@ 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..883ee8a 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_SPINLOCK(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;
 	}
 
+	spin_lock(&bdi_lock);
+	list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
+	spin_unlock(&bdi_lock);
+
 	bdi->dev = dev;
 	bdi_debug_register(bdi, dev_name(dev));
 
@@ -225,9 +231,23 @@ 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)
+{
+	spin_lock(&bdi_lock);
+	list_del_rcu(&bdi->bdi_list);
+	spin_unlock(&bdi_lock);
+
+	/*
+	 * In case the bdi is freed right after unregister, we need to
+	 * make sure any RCU sections have exited
+	 */
+	synchronize_rcu();
+}
+
 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 +265,10 @@ 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 +283,8 @@ 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 +295,10 @@ 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 30351f0..b4c4f7d 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -319,7 +319,6 @@ 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)
-- 
1.6.2.2.446.gfbdc0

[PATCH 03/13] 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.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 fs/buffer.c                 |    2 +-
 fs/fs-writeback.c           |  305 ++++++++++++++++++++++++++-----------------
 fs/ntfs/super.c             |   32 +----
 fs/sync.c                   |    2 +-
 include/linux/backing-dev.h |   28 ++++
 include/linux/fs.h          |    3 +-
 include/linux/writeback.h   |    2 +-
 mm/backing-dev.c            |  198 ++++++++++++++++++++++++++--
 mm/page-writeback.c         |  141 +-------------------
 mm/vmscan.c                 |    2 +-
 10 files changed, 412 insertions(+), 303 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 6a18802..7a4f07b 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 34c8d1d..bc188cb 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 +63,182 @@ 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)
+{
+	/*
+	 * 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;
+		/*
+		 * make above store seen before the task is woken
+		 */
+		smp_mb();
+		wake_up(&bdi->wait);
+	}
+
+	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)
+{
+	long nr_to_write;
+	struct writeback_control wbc = {
+		.bdi		= bdi,
+		.sync_mode	= WB_SYNC_NONE,
+		.nr_to_write	= 0,
+		.for_kupdate	= 1,
+		.range_cyclic	= 1,
+	};
+
+	sync_supers();
+
+	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 void bdi_pdflush(struct backing_dev_info *bdi)
+{
+	struct writeback_control wbc = {
+		.bdi			= bdi,
+		.sync_mode		= WB_SYNC_NONE,
+		.older_than_this	= NULL,
+		.range_cyclic		= 1,
+	};
+	long nr_pages = bdi->wb_arg.nr_pages;
+
+	for (;;) {
+		unsigned long background_thresh, 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) &&
+		    nr_pages <= 0)
+			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;
+		DEFINE_WAIT(wait);
+
+		prepare_to_wait(&bdi->wait, &wait, TASK_INTERRUPTIBLE);
+		wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10);
+		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);
+		finish_wait(&bdi->wait, &wait);
+	}
+
+	return 0;
+}
+
+void bdi_writeback_all(struct super_block *sb, long nr_pages)
+{
+	struct backing_dev_info *bdi;
+
+	rcu_read_lock();
+
+restart:
+	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
+		if (!bdi_has_dirty_io(bdi))
+			continue;
+		if (bdi_start_writeback(bdi, sb, nr_pages))
+			goto restart;
+	}
+
+	rcu_read_unlock();
+}
+
 /**
  *	__mark_inode_dirty -	internal function
  *	@inode: inode to mark
@@ -263,46 +437,6 @@ 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
-	 */
-	rcu_read_lock();
-	list_for_each_entry_rcu(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;
-		}
-	}
-	rcu_read_unlock();
-
-	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.
@@ -461,11 +595,11 @@ __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);
@@ -516,13 +650,6 @@ 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.
@@ -530,16 +657,10 @@ 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
@@ -578,11 +699,6 @@ 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
@@ -591,13 +707,10 @@ 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;
-
-	rcu_read_lock();
-	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
-		generic_sync_bdi_inodes(bdi, wbc, sb, is_blkdev_sb);
-	rcu_read_unlock();
+	if (wbc->bdi)
+		bdi_start_writeback(wbc->bdi, sb, 0);
+	else
+		bdi_writeback_all(sb, 0);
 
 	if (wbc->sync_mode == WB_SYNC_ALL) {
 		struct inode *inode, *old_inode = NULL;
@@ -653,58 +766,6 @@ 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/fs/ntfs/super.c b/fs/ntfs/super.c
index f76951d..c4cb157 100644
--- a/fs/ntfs/super.c
+++ b/fs/ntfs/super.c
@@ -2373,39 +2373,13 @@ static void ntfs_put_super(struct super_block *sb)
 		vol->mftmirr_ino = NULL;
 	}
 	/*
-	 * If any dirty inodes are left, throw away all mft data page cache
-	 * pages to allow a clean umount.  This should never happen any more
-	 * due to mft.c::ntfs_mft_writepage() cleaning all the dirty pages as
-	 * the underlying mft records are written out and cleaned.  If it does,
+	 * We should have no dirty inodes left, due to
+	 * mft.c::ntfs_mft_writepage() cleaning all the dirty pages as
+	 * the underlying mft records are written out and cleaned.
 	 * happen anyway, we want to know...
 	 */
 	ntfs_commit_inode(vol->mft_ino);
 	write_inode_now(vol->mft_ino, 1);
-	if (sb_has_dirty_inodes(sb)) {
-		const char *s1, *s2;
-
-		mutex_lock(&vol->mft_ino->i_mutex);
-		truncate_inode_pages(vol->mft_ino->i_mapping, 0);
-		mutex_unlock(&vol->mft_ino->i_mutex);
-		write_inode_now(vol->mft_ino, 1);
-		if (sb_has_dirty_inodes(sb)) {
-			static const char *_s1 = "inodes";
-			static const char *_s2 = "";
-			s1 = _s1;
-			s2 = _s2;
-		} else {
-			static const char *_s1 = "mft pages";
-			static const char *_s2 = "They have been thrown "
-					"away.  ";
-			s1 = _s1;
-			s2 = _s2;
-		}
-		ntfs_error(sb, "Dirty %s found at umount time.  %sYou should "
-				"run chkdsk.  Please email "
-				"linux-ntfs-dev@lists.sourceforge.net and say "
-				"that you saw this message.  Thank you.", s1,
-				s2);
-	}
 #endif /* NTFS_RW */
 
 	iput(vol->mft_ino);
diff --git a/fs/sync.c b/fs/sync.c
index 7abc65f..3887f10 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -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 --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 86668c7..a848eea 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -24,6 +24,7 @@ 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 */
@@ -39,8 +40,14 @@ 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 backing_dev_info {
 	struct list_head bdi_list;
+	struct rcu_head rcu_head;
 
 	unsigned long ra_pages;	/* max readahead in PAGE_CACHE_SIZE units */
 	unsigned long state;	/* Always use atomic bitops on this */
@@ -60,6 +67,9 @@ struct backing_dev_info {
 
 	struct device *dev;
 
+	struct task_struct	*task;		/* writeback task */
+	wait_queue_head_t	wait;
+	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);
+int bdi_writeback_task(struct backing_dev_info *bdi);
+void bdi_writeback_all(struct super_block *sb, long nr_pages);
+void bdi_add_default_flusher_task(struct backing_dev_info *bdi);
 
 extern spinlock_t 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)
 {
@@ -196,6 +218,7 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
 #define BDI_CAP_EXEC_MAP	0x00000040
 #define BDI_CAP_NO_ACCT_WB	0x00000080
 #define BDI_CAP_SWAP_BACKED	0x00000100
+#define BDI_CAP_FLUSH_FORKER	0x00000200
 
 #define BDI_CAP_VMFLAGS \
 	(BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP)
@@ -265,6 +288,11 @@ 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->capabilities & BDI_CAP_FLUSH_FORKER;
+}
+
 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 1f76516..99a9986 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1989,6 +1989,8 @@ 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 *);
@@ -2106,7 +2108,6 @@ 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 9c1ed1f..0bc5af3 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -99,7 +99,7 @@ static inline void inode_sync_wait(struct inode *inode)
 /*
  * mm/page-writeback.c
  */
-int wakeup_pdflush(long nr_pages);
+int 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 883ee8a..c759449 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>
@@ -16,7 +19,7 @@ EXPORT_SYMBOL(default_unplug_io_fn);
 struct backing_dev_info default_backing_dev_info = {
 	.ra_pages	= VM_MAX_READAHEAD * 1024 / PAGE_CACHE_SIZE,
 	.state		= 0,
-	.capabilities	= BDI_CAP_MAP_COPY,
+	.capabilities	= BDI_CAP_MAP_COPY | BDI_CAP_FLUSH_FORKER,
 	.unplug_io_fn	= default_unplug_io_fn,
 };
 EXPORT_SYMBOL_GPL(default_backing_dev_info);
@@ -24,6 +27,7 @@ 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);
 
 #ifdef CONFIG_DEBUG_FS
 #include <linux/debugfs.h>
@@ -195,6 +199,146 @@ 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
+	 */
+	spin_lock_bh(&bdi_lock);
+	list_add_rcu(&bdi->bdi_list, &bdi_list);
+	spin_unlock_bh(&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);
+	wake_up_bit(&bdi->state, BDI_pending);
+
+	return bdi_writeback_task(bdi);
+}
+
+static int bdi_forker_task(void *ptr)
+{
+	struct backing_dev_info *bdi, *me = ptr;
+
+	for (;;) {
+		DEFINE_WAIT(wait);
+
+		/*
+		 * Should never trigger on the default bdi
+		 */
+		WARN_ON(bdi_has_dirty_io(me));
+
+		prepare_to_wait(&me->wait, &wait, TASK_INTERRUPTIBLE);
+		smp_mb();
+		if (list_empty(&bdi_pending_list))
+			schedule();
+		else {
+repeat:
+			bdi = NULL;
+
+			spin_lock_bh(&bdi_lock);
+			if (!list_empty(&bdi_pending_list)) {
+				bdi = list_entry(bdi_pending_list.next,
+						 struct backing_dev_info,
+						 bdi_list);
+				list_del_init(&bdi->bdi_list);
+			}
+			spin_unlock_bh(&bdi_lock);
+
+			/*
+			 * If no bdi or bdi already got setup, continue
+			 */
+			if (!bdi || bdi->task)
+				continue;
+
+			bdi->task = kthread_run(bdi_start_fn, bdi, "bdi-%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) {
+				struct writeback_control wbc = {
+					.bdi			= bdi,
+					.sync_mode		= WB_SYNC_NONE,
+					.older_than_this	= NULL,
+					.range_cyclic		= 1,
+				};
+
+				/*
+				 * Add this 'bdi' to the back, so we get
+				 * a chance to flush other bdi's to free
+				 * memory.
+				 */
+				spin_lock_bh(&bdi_lock);
+				list_add_tail(&bdi->bdi_list,
+						&bdi_pending_list);
+				spin_unlock_bh(&bdi_lock);
+
+				wbc.nr_to_write = 1024;
+				generic_sync_bdi_inodes(NULL, &wbc);
+				goto repeat;
+			}
+		}
+
+		finish_wait(&me->wait, &wait);
+	}
+
+	return 0;
+}
+
+/*
+ * Grace period has now ended, init bdi->bdi_list and add us to the
+ * list of bdi's that are pending for task creation. Wake up
+ * bdi_forker_task() to finish the job and add us back to the
+ * active bdi_list.
+ */
+static void bdi_add_to_pending(struct rcu_head *head)
+{
+	struct backing_dev_info *bdi;
+
+	bdi = container_of(head, struct backing_dev_info, rcu_head);
+	INIT_LIST_HEAD(&bdi->bdi_list);
+
+	spin_lock(&bdi_lock);
+	list_add_tail(&bdi->bdi_list, &bdi_pending_list);
+	spin_unlock(&bdi_lock);
+
+	wake_up(&default_backing_dev_info.wait);
+}
+
+void bdi_add_default_flusher_task(struct backing_dev_info *bdi)
+{
+	if (test_and_set_bit(BDI_pending, &bdi->state))
+		return;
+
+	spin_lock_bh(&bdi_lock);
+	list_del_rcu(&bdi->bdi_list);
+	spin_unlock_bh(&bdi_lock);
+
+	/*
+	 * We need to wait for the current grace period to end,
+	 * in case others were browsing the bdi_list as well.
+	 * So defer the adding and wakeup to after the RCU
+	 * grace period has ended.
+	 */
+	call_rcu(&bdi->rcu_head, bdi_add_to_pending);
+}
+
 int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 		const char *fmt, ...)
 {
@@ -213,9 +357,23 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 		goto exit;
 	}
 
-	spin_lock(&bdi_lock);
-	list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
-	spin_unlock(&bdi_lock);
+	/*
+	 * 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) {
+			ret = -ENOMEM;
+			goto exit;
+		}
+	} else {
+		spin_lock_bh(&bdi_lock);
+		list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
+		spin_unlock_bh(&bdi_lock);
+	}
 
 	bdi->dev = dev;
 	bdi_debug_register(bdi, dev_name(dev));
@@ -231,11 +389,22 @@ 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)
 {
-	spin_lock(&bdi_lock);
+	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);
+
+	spin_lock_bh(&bdi_lock);
 	list_del_rcu(&bdi->bdi_list);
-	spin_unlock(&bdi_lock);
+	spin_unlock_bh(&bdi_lock);
 
 	/*
 	 * In case the bdi is freed right after unregister, we need to
@@ -247,7 +416,13 @@ 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;
@@ -257,14 +432,15 @@ EXPORT_SYMBOL(bdi_unregister);
 
 int bdi_init(struct backing_dev_info *bdi)
 {
-	int i;
-	int err;
+	int i, err;
 
+	INIT_RCU_HEAD(&bdi->rcu_head);
 	bdi->dev = NULL;
 
 	bdi->min_ratio = 0;
 	bdi->max_ratio = 100;
 	bdi->max_prop_frac = PROP_FRAC_BASE;
+	init_waitqueue_head(&bdi->wait);
 	INIT_LIST_HEAD(&bdi->bdi_list);
 	INIT_LIST_HEAD(&bdi->b_io);
 	INIT_LIST_HEAD(&bdi->b_dirty);
@@ -283,8 +459,6 @@ 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 b4c4f7d..e71e3c2 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.
  *
@@ -541,7 +530,7 @@ 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);
@@ -592,7 +581,7 @@ 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);
 }
 
 void set_page_dirty_balance(struct page *page, int page_mkwrite)
@@ -677,152 +666,36 @@ 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.
- */
-static void background_writeout(unsigned long _min_pages)
-{
-	long min_pages = _min_pages;
-	struct writeback_control wbc = {
-		.bdi		= NULL,
-		.sync_mode	= WB_SYNC_NONE,
-		.older_than_this = NULL,
-		.nr_to_write	= 0,
-		.nonblocking	= 1,
-		.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)
+int wakeup_flusher_threads(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);
+	bdi_writeback_all(NULL, nr_pages);
+	return 0;
 }
 
-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);
-	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)
-{
-	if (pdflush_operation(wb_kupdate, 0) < 0)
-		mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
-}
-
-static void laptop_flush(unsigned long unused)
-{
-	sys_sync();
-}
-
 static void laptop_timer_fn(unsigned long unused)
 {
-	pdflush_operation(laptop_flush, 0);
+	wakeup_flusher_threads(0);
 }
 
 /*
@@ -905,8 +778,6 @@ 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 39fdfb1..89b4f90 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1651,7 +1651,7 @@ 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;
 		}
 
-- 
1.6.2.2.446.gfbdc0

[PATCH 04/13] 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              |  276 ---------------------------------------------
 4 files changed, 6 insertions(+), 289 deletions(-)
 delete mode 100644 mm/pdflush.c

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index bc188cb..816cf8e 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 = 0;
+
 /**
  * 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 0bc5af3..f241794 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 {
@@ -151,7 +140,6 @@ 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 ec73c68..2adb811 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 f2caf96..0000000
--- a/mm/pdflush.c
+++ /dev/null
@@ -1,276 +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 max/min number of pdflush threads. R/W by sysctl at
- * /proc/sys/vm/nr_pdflush_threads_max/min
- */
-int nr_pdflush_threads_max __read_mostly = MAX_PDFLUSH_THREADS;
-int nr_pdflush_threads_min __read_mostly = MIN_PDFLUSH_THREADS;
-
-
-/*
- * 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 nr_pdflush_threads_min and nr_pdflush_threads_max.
- * 
- * - 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) &&
-			    nr_pdflush_threads < nr_pdflush_threads_max) {
-				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 <= nr_pdflush_threads_min)
-			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 = nr_pdflush_threads_min;
-
-	for (i = 0; i < nr_pdflush_threads_min; i++)
-		start_one_pdflush_thread();
-	return 0;
-}
-
-module_init(pdflush_init);
-- 
1.6.2.2.446.gfbdc0

[PATCH 05/13] 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           |  140 +++++++++++++++++-----------
 include/linux/backing-dev.h |   42 +++++----
 mm/backing-dev.c            |  218 ++++++++++++++++++++++++++++--------------
 3 files changed, 256 insertions(+), 144 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 816cf8e..2ec8569 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -46,9 +46,11 @@ int nr_pdflush_threads = 0;
  * 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 +61,38 @@ 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)
+{
+	if (!wb_has_dirty_io(wb))
+		return;
+
+	if (writeback_acquire(wb)) {
+		wb->nr_pages = nr_pages;
+		wb->sb = sb;
+
+		/*
+		 * make above store seen before the task is woken
+		 */
+		smp_mb();
+		wake_up(&wb->wait);
+	}
 }
 
 int bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
@@ -81,21 +102,12 @@ 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;
-		/*
-		 * make above store seen before the task is woken
-		 */
-		smp_mb();
-		wake_up(&bdi->wait);
-	}
-
+	wb_start_writeback(&bdi->wb, sb, nr_pages);
 	return 0;
 }
 
@@ -123,11 +135,11 @@ 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)
 {
 	long nr_to_write;
 	struct writeback_control wbc = {
-		.bdi		= bdi,
+		.bdi		= wb->bdi,
 		.sync_mode	= WB_SYNC_NONE,
 		.nr_to_write	= 0,
 		.for_kupdate	= 1,
@@ -151,15 +163,19 @@ static void bdi_kupdated(struct backing_dev_info *bdi)
 	}
 }
 
-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,
+		.bdi			= wb->bdi,
 		.sync_mode		= WB_SYNC_NONE,
 		.older_than_this	= NULL,
 		.range_cyclic		= 1,
 	};
-	long nr_pages = bdi->wb_arg.nr_pages;
+	long nr_pages = wb->nr_pages;
 
 	for (;;) {
 		unsigned long background_thresh, dirty_thresh;
@@ -173,7 +189,7 @@ 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
@@ -190,13 +206,13 @@ 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;
 		DEFINE_WAIT(wait);
 
-		prepare_to_wait(&bdi->wait, &wait, TASK_INTERRUPTIBLE);
+		prepare_to_wait(&wb->wait, &wait, TASK_INTERRUPTIBLE);
 		wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10);
 		schedule_timeout(wait_jiffies);
 		try_to_freeze();
@@ -215,13 +231,13 @@ 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);
-		finish_wait(&bdi->wait, &wait);
+		writeback_release(wb);
+		finish_wait(&wb->wait, &wait);
 	}
 
 	return 0;
@@ -244,6 +260,14 @@ restart:
 	rcu_read_unlock();
 }
 
+/*
+ * 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
@@ -342,9 +366,10 @@ 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:
@@ -371,16 +396,16 @@ 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);
 }
 
 /*
@@ -388,7 +413,9 @@ 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)
@@ -435,11 +462,10 @@ 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);
 }
 
 /*
@@ -600,20 +626,20 @@ __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;
 
@@ -625,7 +651,7 @@ 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) {
 				/*
@@ -647,7 +673,7 @@ 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 */
@@ -681,7 +707,7 @@ 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;
 	}
 
@@ -689,6 +715,14 @@ 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 a848eea..a0c70f1 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -23,8 +23,8 @@ 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 */
@@ -40,15 +40,23 @@ 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 */
+	wait_queue_head_t	wait;
+	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;
 };
 
 struct backing_dev_info {
-	struct list_head bdi_list;
 	struct rcu_head rcu_head;
-
+	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 */
@@ -65,14 +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 */
-	wait_queue_head_t	wait;
-	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);
-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, long nr_pages);
 void bdi_add_default_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 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 c759449..677a8c6 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -199,17 +199,59 @@ 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_waitqueue_head(&wb->wait);
+	INIT_LIST_HEAD(&wb->b_dirty);
+	INIT_LIST_HEAD(&wb->b_io);
+	INIT_LIST_HEAD(&wb->b_more_io);
+}
+
+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);
+}
+
+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;
-
-	/*
-	 * Add us to the active bdi_list
-	 */
-	spin_lock_bh(&bdi_lock);
-	list_add_rcu(&bdi->bdi_list, &bdi_list);
-	spin_unlock_bh(&bdi_lock);
+	int ret;
 
 	tsk->flags |= PF_FLUSHER | PF_SWAPWRITE;
 	set_freezable();
@@ -225,77 +267,81 @@ static int bdi_start_fn(void *ptr)
 	clear_bit(BDI_pending, &bdi->state);
 	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 int bdi_forker_task(void *ptr)
 {
-	struct backing_dev_info *bdi, *me = ptr;
+	struct bdi_writeback *me = ptr;
 
 	for (;;) {
+		struct backing_dev_info *bdi;
+		struct bdi_writeback *wb;
 		DEFINE_WAIT(wait);
 
 		/*
 		 * Should never trigger on the default bdi
 		 */
-		WARN_ON(bdi_has_dirty_io(me));
+		if (wb_has_dirty_io(me)) {
+			bdi_flush_io(me->bdi);
+			WARN_ON(1);
+		}
 
 		prepare_to_wait(&me->wait, &wait, TASK_INTERRUPTIBLE);
+
 		smp_mb();
 		if (list_empty(&bdi_pending_list))
 			schedule();
-		else {
+
+		finish_wait(&me->wait, &wait);
 repeat:
-			bdi = NULL;
+		bdi = NULL;
+		spin_lock_bh(&bdi_lock);
+		if (!list_empty(&bdi_pending_list)) {
+			bdi = list_entry(bdi_pending_list.next,
+					 struct backing_dev_info, bdi_list);
+			list_del_init(&bdi->bdi_list);
+		}
+		spin_unlock_bh(&bdi_lock);
 
-			spin_lock_bh(&bdi_lock);
-			if (!list_empty(&bdi_pending_list)) {
-				bdi = list_entry(bdi_pending_list.next,
-						 struct backing_dev_info,
-						 bdi_list);
-				list_del_init(&bdi->bdi_list);
-			}
-			spin_unlock_bh(&bdi_lock);
+		if (!bdi)
+			continue;
 
-			/*
-			 * If no bdi or bdi already got setup, continue
-			 */
-			if (!bdi || bdi->task)
-				continue;
+		wb = bdi_new_wb(bdi);
+		if (!wb)
+			goto readd_flush;
 
-			bdi->task = kthread_run(bdi_start_fn, bdi, "bdi-%s",
+		wb->task = kthread_run(bdi_start_fn, wb, "bdi-%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:
 			/*
-			 * 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.
+			 * Add this 'bdi' to the back, so we get
+			 * a chance to flush other bdi's to free
+			 * memory.
 			 */
-			if (!bdi->task) {
-				struct writeback_control wbc = {
-					.bdi			= bdi,
-					.sync_mode		= WB_SYNC_NONE,
-					.older_than_this	= NULL,
-					.range_cyclic		= 1,
-				};
-
-				/*
-				 * Add this 'bdi' to the back, so we get
-				 * a chance to flush other bdi's to free
-				 * memory.
-				 */
-				spin_lock_bh(&bdi_lock);
-				list_add_tail(&bdi->bdi_list,
-						&bdi_pending_list);
-				spin_unlock_bh(&bdi_lock);
-
-				wbc.nr_to_write = 1024;
-				generic_sync_bdi_inodes(NULL, &wbc);
-				goto repeat;
-			}
-		}
+			spin_lock_bh(&bdi_lock);
+			list_add_tail(&bdi->bdi_list, &bdi_pending_list);
+			spin_unlock_bh(&bdi_lock);
 
-		finish_wait(&me->wait, &wait);
+			bdi_flush_io(bdi);
+			goto repeat;
+		}
 	}
 
 	return 0;
@@ -318,11 +364,21 @@ static void bdi_add_to_pending(struct rcu_head *head)
 	list_add_tail(&bdi->bdi_list, &bdi_pending_list);
 	spin_unlock(&bdi_lock);
 
-	wake_up(&default_backing_dev_info.wait);
+	wake_up(&default_backing_dev_info.wb.wait);
 }
 
+/*
+ * 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;
 
@@ -363,9 +419,18 @@ 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 exit;
+		}
+
+		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;
 			goto exit;
 		}
@@ -395,34 +460,44 @@ 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
+	 * Make sure nobody finds us on the bdi_list anymore
 	 */
 	wait_on_bit(&bdi->state, BDI_pending, sched_wait, TASK_UNINTERRUPTIBLE);
 
+	/*
+	 * Make sure nobody finds us on the bdi_list anymore
+	 */
 	spin_lock_bh(&bdi_lock);
 	list_del_rcu(&bdi->bdi_list);
 	spin_unlock_bh(&bdi_lock);
 
 	/*
-	 * In case the bdi is freed right after unregister, we need to
-	 * make sure any RCU sections have exited
+	 * Now make sure that anybody who is currently looking at us from
+	 * the bdi_list iteration have exited.
 	 */
 	synchronize_rcu();
+
+	/*
+	 * 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;
@@ -440,11 +515,10 @@ int bdi_init(struct backing_dev_info *bdi)
 	bdi->min_ratio = 0;
 	bdi->max_ratio = 100;
 	bdi->max_prop_frac = PROP_FRAC_BASE;
-	init_waitqueue_head(&bdi->wait);
 	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);
@@ -469,9 +543,7 @@ 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);
 
-- 
1.6.2.2.446.gfbdc0

[PATCH 06/13] 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           |   47 ++++++++++-
 include/linux/backing-dev.h |   15 ++++
 include/linux/fs.h          |    3 +
 mm/backing-dev.c            |  185 +++++++++++++++++++++++++++++++++++--------
 4 files changed, 211 insertions(+), 39 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 2ec8569..756714f 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -98,16 +98,30 @@ static void wb_start_writeback(struct bdi_writeback *wb, struct super_block *sb,
 int bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
 			 long nr_pages)
 {
+	struct bdi_writeback *wb;
+
 	/*
 	 * This only happens the first time someone kicks this bdi, so put
 	 * it out-of-line.
 	 */
-	if (unlikely(!bdi->wb.task)) {
+	if (unlikely(list_empty_careful(&bdi->wb_list))) {
 		bdi_add_default_flusher_task(bdi);
 		return 1;
 	}
 
-	wb_start_writeback(&bdi->wb, sb, nr_pages);
+	if (!bdi_wblist_needs_lock(bdi))
+		wb_start_writeback(&bdi->wb, sb, nr_pages);
+	else {
+		int idx;
+
+		idx = srcu_read_lock(&bdi->srcu);
+
+		list_for_each_entry_rcu(wb, &bdi->wb_list, list)
+			wb_start_writeback(wb, sb, nr_pages);
+
+		srcu_read_unlock(&bdi->srcu, idx);
+	}
+
 	return 0;
 }
 
@@ -261,11 +275,18 @@ restart:
 }
 
 /*
- * 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);
 }
 
 /**
@@ -719,8 +740,24 @@ void generic_sync_bdi_inodes(struct super_block *sb,
 			     struct writeback_control *wbc)
 {
 	struct backing_dev_info *bdi = wbc->bdi;
+	struct bdi_writeback *wb;
+
+	/*
+	 * 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;
 
-	generic_sync_wb_inodes(&bdi->wb, sb, wbc);
+		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);
+	}
 }
 
 /*
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index a0c70f1..c596bf6 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/srcu.h>
 #include <asm/atomic.h>
 
 struct page;
@@ -25,6 +26,7 @@ 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 */
@@ -41,6 +43,8 @@ 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;
 
@@ -54,8 +58,11 @@ struct bdi_writeback {
 	struct super_block	*sb;
 };
 
+#define BDI_MAX_FLUSHERS	32
+
 struct backing_dev_info {
 	struct rcu_head rcu_head;
+	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 */
@@ -74,6 +81,8 @@ struct backing_dev_info {
 	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_active;  /* bitmap of active tasks */
 	unsigned long wb_mask;	  /* number of registered tasks */
 
@@ -97,11 +106,17 @@ int bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
 int bdi_writeback_task(struct bdi_writeback *wb);
 void bdi_writeback_all(struct super_block *sb, long nr_pages);
 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 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) ||
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 99a9986..9e25cbb 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1477,11 +1477,14 @@ 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/mm/backing-dev.c b/mm/backing-dev.c
index 677a8c6..4ebcc49 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -225,24 +225,48 @@ static void bdi_flush_io(struct backing_dev_info *bdi)
 
 static int wb_assign_nr(struct backing_dev_info *bdi, struct bdi_writeback *wb)
 {
-	set_bit(0, &bdi->wb_mask);
-	wb->nr = 0;
+	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;
 	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 (wb == &bdi->wb)
+		clear_bit(BDI_wb_alloc, &bdi->state);
+	else
+		kfree(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);
+	if (!test_and_set_bit(BDI_wb_alloc, &bdi->state)) {
+		wb = &bdi->wb;
+		wb_assign_nr(bdi, wb);
+	} else {
+		wb = kmalloc(sizeof(struct bdi_writeback), GFP_KERNEL);
+		if (wb) {
+			bdi_wb_init(wb, bdi);
+			if (wb_assign_nr(bdi, wb)) {
+				kfree(wb);
+				wb = NULL;
+			}
+		}
+	}
+
 	return wb;
 }
 
@@ -251,7 +275,22 @@ static int bdi_start_fn(void *ptr)
 	struct bdi_writeback *wb = ptr;
 	struct backing_dev_info *bdi = wb->bdi;
 	struct task_struct *tsk = current;
-	int ret;
+	int was_empty, ret;
+
+	/*
+	 * 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();
@@ -269,13 +308,44 @@ 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 int bdi_forker_task(void *ptr)
@@ -367,33 +437,73 @@ static void bdi_add_to_pending(struct rcu_head *head)
 	wake_up(&default_backing_dev_info.wb.wait);
 }
 
-/*
- * 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)
+static int sched_wait(void *word)
+{
+	schedule();
+	return 0;
+}
+
+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)) {
+		spin_lock_bh(&bdi_lock);
+		list_del_rcu(&bdi->bdi_list);
+		spin_unlock_bh(&bdi_lock);
 
-	spin_lock_bh(&bdi_lock);
-	list_del_rcu(&bdi->bdi_list);
-	spin_unlock_bh(&bdi_lock);
+		/*
+		 * We need to wait for the current grace period to end,
+		 * in case others were browsing the bdi_list as well.
+		 * So defer the adding and wakeup to after the RCU
+		 * grace period has ended.
+		 */
+		call_rcu(&bdi->rcu_head, bdi_add_to_pending);
+	}
+}
 
-	/*
-	 * We need to wait for the current grace period to end,
-	 * in case others were browsing the bdi_list as well.
-	 * So defer the adding and wakeup to after the RCU
-	 * grace period has ended.
-	 */
-	call_rcu(&bdi->rcu_head, bdi_add_to_pending);
+static int flusher_add_helper_block(struct backing_dev_info *bdi)
+{
+	wait_on_bit_lock(&bdi->state, BDI_pending, sched_wait,
+				TASK_UNINTERRUPTIBLE);
+	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)
+{
+	bdi_add_one_flusher_task(bdi, flusher_add_helper_block);
 }
+EXPORT_SYMBOL(bdi_add_flusher_task);
 
 int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 		const char *fmt, ...)
@@ -454,17 +564,13 @@ 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;
 
@@ -488,9 +594,11 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi)
 	synchronize_rcu();
 
 	/*
-	 * 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)
@@ -515,7 +623,9 @@ 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);
 	INIT_LIST_HEAD(&bdi->bdi_list);
+	INIT_LIST_HEAD(&bdi->wb_list);
 	bdi->wb_mask = bdi->wb_active = 0;
 
 	bdi_wb_init(&bdi->wb, bdi);
@@ -526,10 +636,15 @@ 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]);
@@ -547,6 +662,8 @@ 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]);
 
-- 
1.6.2.2.446.gfbdc0

[PATCH 07/13] writeback: include default_backing_dev_info in writeback

[Jens Axboe]

We see dirty inodes there occasionally, so better be safe and write them
out.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 fs/fs-writeback.c         |   60 ++++++++++++++++++++++++++------------------
 include/linux/writeback.h |    1 +
 mm/backing-dev.c          |   31 ++++++++++++++---------
 3 files changed, 55 insertions(+), 37 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 756714f..bcca7c1 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -34,6 +34,10 @@
  */
 int nr_pdflush_threads = 0;
 
+static void generic_sync_wb_inodes(struct bdi_writeback *wb,
+				   struct super_block *sb,
+				   struct writeback_control *wbc);
+
 /**
  * writeback_acquire - attempt to get exclusive writeback access to a device
  * @bdi: the device's backing_dev_info structure
@@ -149,7 +153,7 @@ 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 wb_kupdated(struct bdi_writeback *wb)
+void wb_kupdated(struct bdi_writeback *wb)
 {
 	long nr_to_write;
 	struct writeback_control wbc = {
@@ -177,11 +181,7 @@ static void wb_kupdated(struct bdi_writeback *wb)
 	}
 }
 
-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)
+void wb_writeback(struct bdi_writeback *wb)
 {
 	struct writeback_control wbc = {
 		.bdi			= wb->bdi,
@@ -217,6 +217,34 @@ static void 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
+ */
+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, 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);
+}
+
+/*
  * Handle writeback of dirty data for the device backed by this bdi. Also
  * wakes up periodically and does kupdated style flushing.
  */
@@ -231,26 +259,8 @@ int bdi_writeback_task(struct bdi_writeback *wb)
 		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);
+		wb_do_writeback(wb);
 
-		writeback_release(wb);
 		finish_wait(&wb->wait, &wait);
 	}
 
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index f241794..2e08bbd 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -69,6 +69,7 @@ void writeback_inodes(struct writeback_control *wbc);
 int inode_wait(void *);
 void sync_inodes_sb(struct super_block *, int wait);
 void sync_inodes(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 4ebcc49..9707545 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -357,14 +357,6 @@ static int bdi_forker_task(void *ptr)
 		struct bdi_writeback *wb;
 		DEFINE_WAIT(wait);
 
-		/*
-		 * Should never trigger on the default bdi
-		 */
-		if (wb_has_dirty_io(me)) {
-			bdi_flush_io(me->bdi);
-			WARN_ON(1);
-		}
-
 		prepare_to_wait(&me->wait, &wait, TASK_INTERRUPTIBLE);
 
 		smp_mb();
@@ -372,6 +364,21 @@ static int bdi_forker_task(void *ptr)
 			schedule();
 
 		finish_wait(&me->wait, &wait);
+
+		/*
+		 * Ideally we'd like not to see any dirty inodes on the
+		 * default_backing_dev_info. Until these are tracked down,
+		 * perform the same writeback here that bdi_writeback_task
+		 * does. For logic, see comment in
+		 * fs/fs-writeback.c:bdi_writeback_task()
+		 */
+		if (wb_has_dirty_io(me))
+			wb_do_writeback(me);
+
+		/*
+		 * This is our real job - check for pending entries in
+		 * bdi_pending_list, and create the tasks that got added
+		 */
 repeat:
 		bdi = NULL;
 		spin_lock_bh(&bdi_lock);
@@ -544,12 +551,12 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 			ret = -ENOMEM;
 			goto exit;
 		}
-	} else {
-		spin_lock_bh(&bdi_lock);
-		list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
-		spin_unlock_bh(&bdi_lock);
 	}
 
+	spin_lock_bh(&bdi_lock);
+	list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
+	spin_unlock_bh(&bdi_lock);
+
 	bdi->dev = dev;
 	bdi_debug_register(bdi, dev_name(dev));
 
-- 
1.6.2.2.446.gfbdc0

[PATCH 08/13] 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           |   44 +++++++++++++++++++++++++++++++++++-------
 include/linux/backing-dev.h |    5 ++++
 include/linux/writeback.h   |    2 +-
 3 files changed, 42 insertions(+), 9 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index bcca7c1..7ed86a0 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -153,9 +153,9 @@ 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.
  */
-void wb_kupdated(struct bdi_writeback *wb)
+long wb_kupdated(struct bdi_writeback *wb)
 {
-	long nr_to_write;
+	long nr_to_write, wrote = 0;
 	struct writeback_control wbc = {
 		.bdi		= wb->bdi,
 		.sync_mode	= WB_SYNC_NONE,
@@ -175,13 +175,16 @@ void wb_kupdated(struct bdi_writeback *wb)
 		wbc.encountered_congestion = 0;
 		wbc.nr_to_write = MAX_WRITEBACK_PAGES;
 		generic_sync_bdi_inodes(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;
 }
 
-void wb_writeback(struct bdi_writeback *wb)
+long wb_writeback(struct bdi_writeback *wb)
 {
 	struct writeback_control wbc = {
 		.bdi			= wb->bdi,
@@ -189,7 +192,7 @@ void wb_writeback(struct bdi_writeback *wb)
 		.older_than_this	= NULL,
 		.range_cyclic		= 1,
 	};
-	long nr_pages = wb->nr_pages;
+	long nr_pages = wb->nr_pages, wrote = 0;
 
 	for (;;) {
 		unsigned long background_thresh, dirty_thresh;
@@ -205,6 +208,7 @@ void wb_writeback(struct bdi_writeback *wb)
 		wbc.pages_skipped = 0;
 		generic_sync_wb_inodes(wb, 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
 		 */
@@ -214,14 +218,18 @@ void wb_writeback(struct bdi_writeback *wb)
 			break;
 		}
 	}
+
+	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 nr_pages;
+
 	/*
 	 * We get here in two cases:
 	 *
@@ -237,11 +245,12 @@ void wb_do_writeback(struct bdi_writeback *wb)
 	 *
 	 */
 	if (writeback_acquire(wb))
-		wb_kupdated(wb);
+		nr_pages = wb_kupdated(wb);
 	else
-		wb_writeback(wb);
+		nr_pages = wb_writeback(wb);
 
 	writeback_release(wb);
+	return nr_pages;
 }
 
 /*
@@ -250,6 +259,9 @@ void wb_do_writeback(struct bdi_writeback *wb)
  */
 int bdi_writeback_task(struct bdi_writeback *wb)
 {
+	unsigned long last_active = jiffies;
+	long pages_written;
+
 	while (!kthread_should_stop()) {
 		unsigned long wait_jiffies;
 		DEFINE_WAIT(wait);
@@ -259,9 +271,25 @@ int bdi_writeback_task(struct bdi_writeback *wb)
 		schedule_timeout(wait_jiffies);
 		try_to_freeze();
 
-		wb_do_writeback(wb);
+		pages_written = wb_do_writeback(wb);
 
 		finish_wait(&wb->wait, &wait);
+
+		if (pages_written)
+			last_active = jiffies;
+		else {
+			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;
+		}
 	}
 
 	return 0;
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index c596bf6..ce23ec7 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -112,6 +112,11 @@ 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);
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 2e08bbd..ddb10dc 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -69,7 +69,7 @@ void writeback_inodes(struct writeback_control *wbc);
 int inode_wait(void *);
 void sync_inodes_sb(struct super_block *, int wait);
 void sync_inodes(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)
-- 
1.6.2.2.446.gfbdc0

[PATCH 09/13] writeback: btrfs must register its backing_devices

[Jens Axboe]

btrfs puts dirty inodes on there, so it must register a thread
to handle them. Also fixes failure to check bdi_init() return value,
and bad inherit of ->capabilities flags from the default bdi.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 fs/btrfs/disk-io.c |   23 ++++++++++++++++++-----
 1 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 92caa80..3c91484 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1366,12 +1366,24 @@ 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");
+	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;
@@ -1595,7 +1607,8 @@ 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;
@@ -1951,8 +1964,8 @@ 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);
-- 
1.6.2.2.446.gfbdc0

[PATCH 10/13] writeback: add some debug inode list counters to bdi stats

[Jens Axboe]

Not meant for inclusion, just to monitor what is going on while testing
this stuff.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 mm/backing-dev.c |   32 ++++++++++++++++++++++++++++++--
 1 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 9707545..a45b7d9 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -43,9 +43,33 @@ 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);
+
+	nr_dirty <<= (PAGE_CACHE_SHIFT - 10);
+	nr_io <<= (PAGE_CACHE_SHIFT - 10);
+	nr_more_io <<= (PAGE_CACHE_SHIFT - 10);
 
 	get_dirty_limits(&background_thresh, &dirty_thresh, &bdi_thresh, bdi);
 
@@ -55,12 +79,16 @@ 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 kB\n"
+		   "b_io:             %8lu kB\n"
+		   "b_more_io:        %8lu kB\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(background_thresh), nr_wb, nr_dirty, nr_io, nr_more_io);
 #undef K
 
 	return 0;
-- 
1.6.2.2.446.gfbdc0

[PATCH 11/13] writeback: add name to backing_dev_info

[Jens Axboe]

Just for testing purposes, to be able to easier track who does what.

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 07ab754..226e9da 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -517,6 +517,7 @@ 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.name = "block";
 	err = bdi_init(&q->backing_dev_info);
 	if (err) {
 		kmem_cache_free(blk_requestq_cachep, q);
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 3586b3b..45b485f 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -847,6 +847,7 @@ 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 3c91484..ec19a90 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1374,6 +1374,7 @@ 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 38f7122..350ef9c 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 459b73d..21ed16c 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -481,6 +481,7 @@ 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 23a3c76..91816c7 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 faa44f9..2a63dce 100644
--- a/fs/ubifs/super.c
+++ b/fs/ubifs/super.c
@@ -1923,6 +1923,7 @@ 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 ce23ec7..a343719 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -72,6 +72,8 @@ 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 382109b..b4ed39a 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -598,6 +598,7 @@ 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 a45b7d9..f86f9cc 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 | BDI_CAP_FLUSH_FORKER,
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 3ecea98..323da00 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,
 };
-- 
1.6.2.2.446.gfbdc0

[PATCH 12/13] 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 7ed86a0..1d25d3a 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -426,6 +426,13 @@ 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 a343719..c7c1ed6 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -29,6 +29,7 @@ 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 f86f9cc..9d6ac11 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -485,6 +485,11 @@ 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
@@ -588,6 +593,7 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 
 	bdi->dev = dev;
 	bdi_debug_register(bdi, dev_name(dev));
+	set_bit(BDI_registered, &bdi->state);
 
 exit:
 	return ret;
-- 
1.6.2.2.446.gfbdc0

[PATCH 13/13] writeback: ensure consistency for generic_sync_sb_inodes() with WB_SYNC_ALL

[Jens Axboe]

If WB_SYNC_ALL is given, we must block waiting for any bdi/wb to become
available and flush our data. Switch the bdi_list protection to SRCU
instead of RCU so that we can do that.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 fs/fs-writeback.c           |   49 +++++++++++++++++++++++++++++--------------
 include/linux/backing-dev.h |   12 ++++++++-
 mm/backing-dev.c            |   23 ++++++++++++--------
 mm/page-writeback.c         |    4 +-
 4 files changed, 59 insertions(+), 29 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 1d25d3a..0492399 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -50,11 +50,18 @@ static void generic_sync_wb_inodes(struct bdi_writeback *wb,
  * unless they implement their own.  Which is somewhat inefficient, as this
  * may prevent concurrent writeback against multiple devices.
  */
-static int writeback_acquire(struct bdi_writeback *wb)
+static bool writeback_acquire(struct bdi_writeback *wb, int wait)
 {
 	struct backing_dev_info *bdi = wb->bdi;
 
-	return !test_and_set_bit(wb->nr, &bdi->wb_active);
+	if (!test_and_set_bit(wb->nr, &bdi->wb_active))
+		return 1;
+	if (!wait)
+		return 0;
+
+	wait_on_bit_lock(&bdi->wb_active, wb->nr, bdi_sched_wait,
+				TASK_UNINTERRUPTIBLE);
+	return 1;
 }
 
 /**
@@ -82,12 +89,15 @@ static void writeback_release(struct bdi_writeback *wb)
 }
 
 static void wb_start_writeback(struct bdi_writeback *wb, struct super_block *sb,
-			       long nr_pages)
+			       long nr_pages, int wait)
 {
 	if (!wb_has_dirty_io(wb))
 		return;
 
-	if (writeback_acquire(wb)) {
+	/*
+	 * Wait is set, block waiting for the device to become available
+	 */
+	if (writeback_acquire(wb, wait)) {
 		wb->nr_pages = nr_pages;
 		wb->sb = sb;
 
@@ -100,7 +110,7 @@ static void wb_start_writeback(struct bdi_writeback *wb, struct super_block *sb,
 }
 
 int bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
-			 long nr_pages)
+			 long nr_pages, int wait)
 {
 	struct bdi_writeback *wb;
 
@@ -114,14 +124,14 @@ int bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
 	}
 
 	if (!bdi_wblist_needs_lock(bdi))
-		wb_start_writeback(&bdi->wb, sb, nr_pages);
+		wb_start_writeback(&bdi->wb, sb, nr_pages, wait);
 	else {
 		int idx;
 
 		idx = srcu_read_lock(&bdi->srcu);
 
 		list_for_each_entry_rcu(wb, &bdi->wb_list, list)
-			wb_start_writeback(wb, sb, nr_pages);
+			wb_start_writeback(wb, sb, nr_pages, wait);
 
 		srcu_read_unlock(&bdi->srcu, idx);
 	}
@@ -244,7 +254,7 @@ long wb_do_writeback(struct bdi_writeback *wb)
 	 *  pdflush style writeout.
 	 *
 	 */
-	if (writeback_acquire(wb))
+	if (writeback_acquire(wb, 0))
 		nr_pages = wb_kupdated(wb);
 	else
 		nr_pages = wb_writeback(wb);
@@ -295,21 +305,21 @@ int bdi_writeback_task(struct bdi_writeback *wb)
 	return 0;
 }
 
-void bdi_writeback_all(struct super_block *sb, long nr_pages)
+void bdi_writeback_all(struct super_block *sb, long nr_pages, int wait)
 {
 	struct backing_dev_info *bdi;
+	int idx;
 
-	rcu_read_lock();
-
+	idx = srcu_read_lock(&bdi_srcu);
 restart:
 	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
 		if (!bdi_has_dirty_io(bdi))
 			continue;
-		if (bdi_start_writeback(bdi, sb, nr_pages))
+		if (bdi_start_writeback(bdi, sb, nr_pages, wait))
 			goto restart;
 	}
 
-	rcu_read_unlock();
+	srcu_read_unlock(&bdi_srcu, idx);
 }
 
 /*
@@ -828,12 +838,19 @@ void generic_sync_bdi_inodes(struct super_block *sb,
 void generic_sync_sb_inodes(struct super_block *sb,
 				struct writeback_control *wbc)
 {
+	const int sync_all = wbc->sync_mode == WB_SYNC_ALL;
+
+	/*
+	 * Kick off the specified bdi, if given, or all of them. If sync_all
+	 * is true, then this is a blocking operation and we must make sure
+	 * to wait for any device that is currently doing a writeback operation.
+	 */
 	if (wbc->bdi)
-		bdi_start_writeback(wbc->bdi, sb, 0);
+		bdi_start_writeback(wbc->bdi, sb, 0, sync_all);
 	else
-		bdi_writeback_all(sb, 0);
+		bdi_writeback_all(sb, 0, sync_all);
 
-	if (wbc->sync_mode == WB_SYNC_ALL) {
+	if (sync_all) {
 		struct inode *inode, *old_inode = NULL;
 
 		spin_lock(&inode_lock);
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index c7c1ed6..8ab2429 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -14,6 +14,7 @@
 #include <linux/kernel.h>
 #include <linux/fs.h>
 #include <linux/srcu.h>
+#include <linux/sched.h>
 #include <asm/atomic.h>
 
 struct page;
@@ -105,15 +106,22 @@ 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);
 int bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
-			 long nr_pages);
+			 long nr_pages, int wait);
 int bdi_writeback_task(struct bdi_writeback *wb);
-void bdi_writeback_all(struct super_block *sb, long nr_pages);
+void bdi_writeback_all(struct super_block *sb, long nr_pages, int wait);
 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;
+extern struct srcu_struct bdi_srcu;
+
+static inline int bdi_sched_wait(void *word)
+{
+	schedule();
+	return 0;
+}
 
 static inline int wb_is_default_task(struct bdi_writeback *wb)
 {
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 9d6ac11..8ee7b55 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -29,6 +29,7 @@ static struct class *bdi_class;
 DEFINE_SPINLOCK(bdi_lock);
 LIST_HEAD(bdi_list);
 LIST_HEAD(bdi_pending_list);
+struct srcu_struct bdi_srcu;
 
 #ifdef CONFIG_DEBUG_FS
 #include <linux/debugfs.h>
@@ -220,10 +221,19 @@ static int __init default_bdi_init(void)
 {
 	int err;
 
+	err = init_srcu_struct(&bdi_srcu);
+	if (err)
+		return err;
+
 	err = bdi_init(&default_backing_dev_info);
 	if (!err)
 		bdi_register(&default_backing_dev_info, NULL, "default");
 
+	if (err) {
+		bdi_destroy(&default_backing_dev_info);
+		cleanup_srcu_struct(&bdi_srcu);
+	}
+
 	return err;
 }
 subsys_initcall(default_bdi_init);
@@ -473,12 +483,6 @@ static void bdi_add_to_pending(struct rcu_head *head)
 	wake_up(&default_backing_dev_info.wb.wait);
 }
 
-static int sched_wait(void *word)
-{
-	schedule();
-	return 0;
-}
-
 static void bdi_add_one_flusher_task(struct backing_dev_info *bdi,
 				     int(*func)(struct backing_dev_info *))
 {
@@ -513,7 +517,7 @@ static void bdi_add_one_flusher_task(struct backing_dev_info *bdi,
 
 static int flusher_add_helper_block(struct backing_dev_info *bdi)
 {
-	wait_on_bit_lock(&bdi->state, BDI_pending, sched_wait,
+	wait_on_bit_lock(&bdi->state, BDI_pending, bdi_sched_wait,
 				TASK_UNINTERRUPTIBLE);
 	return 0;
 }
@@ -620,7 +624,8 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi)
 	 * If setup is pending, wait for that to complete first
 	 * Make sure nobody finds us on the bdi_list anymore
 	 */
-	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
@@ -633,7 +638,7 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi)
 	 * Now make sure that anybody who is currently looking at us from
 	 * the bdi_list iteration have exited.
 	 */
-	synchronize_rcu();
+	synchronize_srcu(&bdi_srcu);
 
 	/*
 	 * 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 e71e3c2..bac4ad6 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -581,7 +581,7 @@ 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)))
-		bdi_start_writeback(bdi, NULL, 0);
+		bdi_start_writeback(bdi, NULL, 0, 0);
 }
 
 void set_page_dirty_balance(struct page *page, int page_mkwrite)
@@ -675,7 +675,7 @@ int wakeup_flusher_threads(long nr_pages)
 	if (nr_pages == 0)
 		nr_pages = global_page_state(NR_FILE_DIRTY) +
 				global_page_state(NR_UNSTABLE_NFS);
-	bdi_writeback_all(NULL, nr_pages);
+	bdi_writeback_all(NULL, nr_pages, 0);
 	return 0;
 }
 
-- 
1.6.2.2.446.gfbdc0

Re: [PATCH 0/13] Per-bdi writeback flusher threads #3

[Zhang, Yanmin]

On Wed, 2009-04-08 at 14:00 +0200, Jens Axboe wrote:
> Hi,
> 
> This is the third version of the patchset. Changes since v2:
Jens,

The patchset forgets kernel/sysctl.c part, so the compilation link fails.

Yanmin

> 
> - Dropped some of the prep patches, since they are now in mainline.
>   Unfortunately we grew another pdflush_operation() user (emergency thaw),
>   so I had to introduce a new prep patch for that.
> 
> - Fix the data consistency issue in generic_sync_sb_inodes() with
>   WB_SYNC_ALL that Jan Kara pointed out. I had to switch bdi_list
>   to SRCU protection for this. I pondered using a mutex for bdi_lock,
>   but that does not work with the pending list <-> active list
>   RCU callback scheme.
> 
> - Fix race in bdi task removal, we need to synchronize_rcu() before
>   doing the wb task kill, not after. This ensures that once we do the
>   task kill, nobody is accessing our bdi anymore.
> 
> - Separate default wb task creation from filesystem initiated task
>   additions. The former can be racy and should check the pending bit
>   only to see whether it should proceed, the latter should block waiting
>   for previous task additions to finish.
> 
> - Move the bdi_cap_flusher_forker() back in the series to where the
>   BDI_CAP_FLUSH_FORKER flag was introduced.
> 
> - Fix a problem where the first incremental step ended up writing back
>   all the dirty inodes on a bdi, not just the ones belonging to a
>   specific super_block. Only a problem after the first patch, the 2nd
>   patch in the series got it right again. (Thanks Jan Kara).
> 
> - Allow writeback tasks to exit, if the bdi has been idle for a certain
>   period of time. The lazy create will recreate them if we see dirty
>   inodes on the bdi later on.
> 
> - btrfs must register its fs_info bdi, or direct writeback will not work
>   as intended. Also kill capabilities inherit from
>   default_backing_dev_info and fix failure to check bdi_init() return
>   value.
> 
> The branch can be pulled from:
> 
> git://git.kernel.dk/linux-2.6-block.git writeback
> 
> Or these patches can be applied directly to 2.6.30-rc1.
> 

Re: [PATCH 0/13] Per-bdi writeback flusher threads #3

[Jens Axboe]

On Fri, Apr 10 2009, Zhang, Yanmin wrote:
> On Wed, 2009-04-08 at 14:00 +0200, Jens Axboe wrote:
> > Hi,
> > 
> > This is the third version of the patchset. Changes since v2:
> Jens,
> 
> The patchset forgets kernel/sysctl.c part, so the compilation link fails.

Yep, noticed that as well. Not really great timing with adding more
pdflush tunables...

There's also an issue with the SRCU init, so it will not even work
irregardless of the compilation problem. I'll have to update and repost
next week.

-- 
Jens Axboe

Re: [PATCH 0/13] Per-bdi writeback flusher threads #3

[Zhang, Yanmin]

On Fri, 2009-04-10 at 09:21 +0200, Jens Axboe wrote:
> On Fri, Apr 10 2009, Zhang, Yanmin wrote:
> > On Wed, 2009-04-08 at 14:00 +0200, Jens Axboe wrote:
> > > Hi,
> > > 
> > > This is the third version of the patchset. Changes since v2:
> > Jens,
> > 
> > The patchset forgets kernel/sysctl.c part, so the compilation link fails.
> 
> Yep, noticed that as well. Not really great timing with adding more
> pdflush tunables...
When I run a fio testing with a partition on one of my machines, I hit below bug
checking. It's a  fio_mmap_randwrite_4k_preread testing. I'm not sure if it happens
after the testing and before the next testing, or just happens when the testing is
ongoing. When I see it, next testing stops at the beginning when mounting the partition.

----------------------sys log--------------------

kernel BUG at fs/jbd/journal.c:1166!
invalid opcode: 0000 [#1] SMP 
last sysfs file: /sys/block/sdb/stat
CPU 0 
Modules linked in: igb
Pid: 18329, comm: umount Not tainted 2.6.30-rc1-bdiflusherv3 #1 X8DTN
RIP: 0010:[<ffffffff80344747>]  [<ffffffff80344747>] journal_destroy+0x108/0x1b4
RSP: 0018:ffff8800bd95fe08  EFLAGS: 00010286
RAX: 000000000000c7c7 RBX: ffff8800bc93dc00 RCX: 0000000000000000
RDX: 0000000000000001 RSI: 0000000000000246 RDI: ffff8800bc93dd64
RBP: ffff8800bc93dd64 R08: ffff8800bc93dc88 R09: 00000000bd95fcc0
R10: 0000000000000246 R11: 00000000fffffffb R12: ffff8800bd95fe08
R13: ffff8800bd95fe20 R14: ffff8800bc93dc98 R15: ffff8800bc93dcc8
FS:  00007f3f26c717d0(0000) GS:ffffc20000000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 00007f3f263fe000 CR3: 00000000bc18e000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process umount (pid: 18329, threadinfo ffff8800bd95e000, task ffff8800bcdcdca0)
Stack:
 0000000000000000 ffff8800bcdcdca0 ffffffff8024ddaa ffff8800bd95fe20
 ffff8800bd95fe20 ffffffff802e53ac ffff8800bd95fe38 ffff8800bd0e3a00
 ffff8800a1ff2400 ffff8800bc93b000 ffff8800bb8cb400 0000000000000000
Call Trace:
 [<ffffffff8024ddaa>] ? autoremove_wake_function+0x0/0x2e
 [<ffffffff802e53ac>] ? mb_cache_shrink+0x22/0x9e
 [<ffffffff8032fbcc>] ? ext3_put_super+0x29/0x204
 [<ffffffff802ac7ab>] ? generic_shutdown_super+0x70/0xde
 [<ffffffff802ac83b>] ? kill_block_super+0x22/0x3a
 [<ffffffff802ac8fe>] ? deactivate_super+0x5f/0x77
 [<ffffffff802bf20a>] ? sys_umount+0x2da/0x309
 [<ffffffff8020ba2b>] ? system_call_fastpath+0x16/0x1b
Code: ff 48 8d ab 64 01 00 00 eb 0b fe 45 00 48 89 df e8 cc e8 ff ff 48 89 ef e8 2f e8 3d 00 48 83 7b 60 00 75 e6 48 83 7b 50 00 74 04 <0f> 0b eb fe 48 83 7b 58 00 74 04 0f 0b eb fe fe 83 64 01 00 00 
RIP  [<ffffffff80344747>] journal_destroy+0x108/0x1b4
 RSP <ffff8800bd95fe08>
---[ end trace 14f5ccbafee46eb4 ]---


> 
> There's also an issue with the SRCU init, so it will not even work
> irregardless of the compilation problem. I'll have to update and repost
> next week.
> 

Re: [PATCH 0/13] Per-bdi writeback flusher threads #3

[Jens Axboe]

On Mon, Apr 13 2009, Zhang, Yanmin wrote:
> On Fri, 2009-04-10 at 09:21 +0200, Jens Axboe wrote:
> > On Fri, Apr 10 2009, Zhang, Yanmin wrote:
> > > On Wed, 2009-04-08 at 14:00 +0200, Jens Axboe wrote:
> > > > Hi,
> > > >
> > > > This is the third version of the patchset. Changes since v2:
> > > Jens,
> > >
> > > The patchset forgets kernel/sysctl.c part, so the compilation link fails.
> >
> > Yep, noticed that as well. Not really great timing with adding more
> > pdflush tunables...
> When I run a fio testing with a partition on one of my machines, I hit below bug
> checking. It's a ??? fio_mmap_randwrite_4k_preread testing. I'm not sure if it happens
> after the testing and before the next testing, or just happens when the testing is
> ongoing. When I see it, next testing stops at the beginning when mounting the partition.
> 
> ----------------------sys log--------------------
> 
> kernel BUG at fs/jbd/journal.c:1166!
> invalid opcode: 0000 [#1] SMP
> last sysfs file: /sys/block/sdb/stat
> CPU 0
> Modules linked in: igb
> Pid: 18329, comm: umount Not tainted 2.6.30-rc1-bdiflusherv3 #1 X8DTN
> RIP: 0010:[<ffffffff80344747>]  [<ffffffff80344747>] journal_destroy+0x108/0x1b4
> RSP: 0018:ffff8800bd95fe08  EFLAGS: 00010286
> RAX: 000000000000c7c7 RBX: ffff8800bc93dc00 RCX: 0000000000000000
> RDX: 0000000000000001 RSI: 0000000000000246 RDI: ffff8800bc93dd64
> RBP: ffff8800bc93dd64 R08: ffff8800bc93dc88 R09: 00000000bd95fcc0
> R10: 0000000000000246 R11: 00000000fffffffb R12: ffff8800bd95fe08
> R13: ffff8800bd95fe20 R14: ffff8800bc93dc98 R15: ffff8800bc93dcc8
> FS:  00007f3f26c717d0(0000) GS:ffffc20000000000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> CR2: 00007f3f263fe000 CR3: 00000000bc18e000 CR4: 00000000000006e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Process umount (pid: 18329, threadinfo ffff8800bd95e000, task ffff8800bcdcdca0)
> Stack:
>  0000000000000000 ffff8800bcdcdca0 ffffffff8024ddaa ffff8800bd95fe20
>  ffff8800bd95fe20 ffffffff802e53ac ffff8800bd95fe38 ffff8800bd0e3a00
>  ffff8800a1ff2400 ffff8800bc93b000 ffff8800bb8cb400 0000000000000000
> Call Trace:
>  [<ffffffff8024ddaa>] ? autoremove_wake_function+0x0/0x2e
>  [<ffffffff802e53ac>] ? mb_cache_shrink+0x22/0x9e
>  [<ffffffff8032fbcc>] ? ext3_put_super+0x29/0x204
>  [<ffffffff802ac7ab>] ? generic_shutdown_super+0x70/0xde
>  [<ffffffff802ac83b>] ? kill_block_super+0x22/0x3a
>  [<ffffffff802ac8fe>] ? deactivate_super+0x5f/0x77
>  [<ffffffff802bf20a>] ? sys_umount+0x2da/0x309
>  [<ffffffff8020ba2b>] ? system_call_fastpath+0x16/0x1b
> Code: ff 48 8d ab 64 01 00 00 eb 0b fe 45 00 48 89 df e8 cc e8 ff ff 48 89 ef e8 2f e8 3d 00 48 83 7b 60 00 75 e6 48 83 7b 50 00 74 04 <0f> 0b eb fe 48 83 7b 58 00 74 04 0f 0b eb fe fe 83 64 01 00 00
> RIP  [<ffffffff80344747>] journal_destroy+0x108/0x1b4
>  RSP <ffff8800bd95fe08>
> ---[ end trace 14f5ccbafee46eb4 ]---

This is very strange, I have about zero idea why this would trigger. It
seems to be this:

        J_ASSERT(journal->j_running_transaction == NULL);

in journal_destroy(), presumably complaining that we are trying to kill
a journal that has a running transaction (yes, me read code good).
Jan Kara is on the CC and he appears to have touched that file the most
recently. Jan, any ideas on what might make this trigger?

-- 
Jens Axboe

Re: [PATCH 0/13] Per-bdi writeback flusher threads #3

[Jan Kara]

[-- Attachment #1: Type: text/plain, Size: 4435 bytes --]

On Fri 17-04-09 15:07:03, Jens Axboe wrote:
> On Mon, Apr 13 2009, Zhang, Yanmin wrote:
> > On Fri, 2009-04-10 at 09:21 +0200, Jens Axboe wrote:
> > > On Fri, Apr 10 2009, Zhang, Yanmin wrote:
> > > > On Wed, 2009-04-08 at 14:00 +0200, Jens Axboe wrote:
> > > > > Hi,
> > > > >
> > > > > This is the third version of the patchset. Changes since v2:
> > > > Jens,
> > > >
> > > > The patchset forgets kernel/sysctl.c part, so the compilation link fails.
> > >
> > > Yep, noticed that as well. Not really great timing with adding more
> > > pdflush tunables...
> > When I run a fio testing with a partition on one of my machines, I hit below bug
> > checking. It's a ??? fio_mmap_randwrite_4k_preread testing. I'm not sure if it happens
> > after the testing and before the next testing, or just happens when the testing is
> > ongoing. When I see it, next testing stops at the beginning when mounting the partition.
> > 
> > ----------------------sys log--------------------
> > 
> > kernel BUG at fs/jbd/journal.c:1166!
> > invalid opcode: 0000 [#1] SMP
> > last sysfs file: /sys/block/sdb/stat
> > CPU 0
> > Modules linked in: igb
> > Pid: 18329, comm: umount Not tainted 2.6.30-rc1-bdiflusherv3 #1 X8DTN
> > RIP: 0010:[<ffffffff80344747>]  [<ffffffff80344747>] journal_destroy+0x108/0x1b4
> > RSP: 0018:ffff8800bd95fe08  EFLAGS: 00010286
> > RAX: 000000000000c7c7 RBX: ffff8800bc93dc00 RCX: 0000000000000000
> > RDX: 0000000000000001 RSI: 0000000000000246 RDI: ffff8800bc93dd64
> > RBP: ffff8800bc93dd64 R08: ffff8800bc93dc88 R09: 00000000bd95fcc0
> > R10: 0000000000000246 R11: 00000000fffffffb R12: ffff8800bd95fe08
> > R13: ffff8800bd95fe20 R14: ffff8800bc93dc98 R15: ffff8800bc93dcc8
> > FS:  00007f3f26c717d0(0000) GS:ffffc20000000000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> > CR2: 00007f3f263fe000 CR3: 00000000bc18e000 CR4: 00000000000006e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> > Process umount (pid: 18329, threadinfo ffff8800bd95e000, task ffff8800bcdcdca0)
> > Stack:
> >  0000000000000000 ffff8800bcdcdca0 ffffffff8024ddaa ffff8800bd95fe20
> >  ffff8800bd95fe20 ffffffff802e53ac ffff8800bd95fe38 ffff8800bd0e3a00
> >  ffff8800a1ff2400 ffff8800bc93b000 ffff8800bb8cb400 0000000000000000
> > Call Trace:
> >  [<ffffffff8024ddaa>] ? autoremove_wake_function+0x0/0x2e
> >  [<ffffffff802e53ac>] ? mb_cache_shrink+0x22/0x9e
> >  [<ffffffff8032fbcc>] ? ext3_put_super+0x29/0x204
> >  [<ffffffff802ac7ab>] ? generic_shutdown_super+0x70/0xde
> >  [<ffffffff802ac83b>] ? kill_block_super+0x22/0x3a
> >  [<ffffffff802ac8fe>] ? deactivate_super+0x5f/0x77
> >  [<ffffffff802bf20a>] ? sys_umount+0x2da/0x309
> >  [<ffffffff8020ba2b>] ? system_call_fastpath+0x16/0x1b
> > Code: ff 48 8d ab 64 01 00 00 eb 0b fe 45 00 48 89 df e8 cc e8 ff ff 48 89 ef e8 2f e8 3d 00 48 83 7b 60 00 75 e6 48 83 7b 50 00 74 04 <0f> 0b eb fe 48 83 7b 58 00 74 04 0f 0b eb fe fe 83 64 01 00 00
> > RIP  [<ffffffff80344747>] journal_destroy+0x108/0x1b4
> >  RSP <ffff8800bd95fe08>
> > ---[ end trace 14f5ccbafee46eb4 ]---
> 
> This is very strange, I have about zero idea why this would trigger. It
> seems to be this:
> 
>         J_ASSERT(journal->j_running_transaction == NULL);
> 
> in journal_destroy(), presumably complaining that we are trying to kill
> a journal that has a running transaction (yes, me read code good).
> Jan Kara is on the CC and he appears to have touched that file the most
> recently. Jan, any ideas on what might make this trigger?
  I've looked into this. What I think is happening:
we umount the filesystem
fsync_super(sb)
  __fsync_super(sb)
    sync_inode_sb(sb, 0) -> submits some inodes
    ...
    ext3_sync_fs() -> wait for transaction commit
    ...
    sync_inodes_sb(sb, 1) -> submits further IO which did not happen before
      -> transaction started
ext3_put_super()
  journal_destroy() -> BUG

  So obviously it has changed how sync_inodes_sb() work. Now the fact that
ext3 relies on all the IO being submitted during sync_inode_sb() is fragile
to say the least (although during umount not that much) - actually a
similar problem is in sys_sync() path... Attached patch should fix it -
it's not final since the sys_sync() path needs some more tweaking but it
should work at least for common filesystems ;).

									Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR

[-- Attachment #2: 0001-vfs-Write-inodes-reliably-before-calling-write_su.patch --]
[-- Type: text/x-patch, Size: 2562 bytes --]

>From 615ee076495ca9264ef09040f56eae54004e4c26 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
Date: Tue, 21 Apr 2009 14:24:01 +0200
Subject: [PATCH] vfs: Write inodes reliably before calling ->write_super() and ->sync_fs()

So far, __fsync_super() and do_sync() called sync_inodes(sb, 0), then called
->write_super(), ->sync_fs() and after that called sync_inodes(sb, 1). This
ordering makes it kind of hard for filesystems as sync_inodes(sb, 0) need not
submit all the IO (for example it skips inodes with I_SYNC set) so e.g. forcing
transaction to disk in ->sync_fs() is not really enough. Yes, it means sys_sync
has not been completely reliable on some filesystems (ext3, ext4, reiserfs,
ocfs2 and others are hit by this) when racing e.g. with background writeback. A
similar problem hits also other filesystems (e.g. ext2) because of
write_super() being called before the sync_inodes(sb, 1). Change the ordering
so that inodes are first reliably written out and write_super() and sync_fs()
are called only after that.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/super.c |    2 +-
 fs/sync.c  |    9 +++++++--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index 786fe7d..4c12918 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -267,6 +267,7 @@ void __fsync_super(struct super_block *sb)
 {
 	sync_inodes_sb(sb, 0);
 	vfs_dq_sync(sb);
+	sync_inodes_sb(sb, 1);
 	lock_super(sb);
 	if (sb->s_dirt && sb->s_op->write_super)
 		sb->s_op->write_super(sb);
@@ -274,7 +275,6 @@ void __fsync_super(struct super_block *sb)
 	if (sb->s_op->sync_fs)
 		sb->s_op->sync_fs(sb, 1);
 	sync_blockdev(sb->s_bdev);
-	sync_inodes_sb(sb, 1);
 }
 
 /*
diff --git a/fs/sync.c b/fs/sync.c
index 7abc65f..4de4c89 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -26,10 +26,15 @@ static void do_sync(unsigned long wait)
 	wakeup_pdflush(0);
 	sync_inodes(0);		/* All mappings, inodes and their blockdevs */
 	vfs_dq_sync(NULL);
-	sync_supers();		/* Write the superblocks */
 	sync_filesystems(0);	/* Start syncing the filesystems */
+	/*
+	 * We have to reliably submit IO for all the inodes before writing
+	 * super blocks and calling sync_fs(). Otherwise superblock could miss
+	 * some updates or journal could still have uncommitted data.
+	 */
+	sync_inodes(wait);	
+	sync_supers();		/* Write the superblocks */
 	sync_filesystems(wait);	/* Waitingly sync the filesystems */
-	sync_inodes(wait);	/* Mappings, inodes and blockdevs, again. */
 	if (!wait)
 		printk("Emergency Sync complete\n");
 	if (unlikely(laptop_mode))
-- 
1.6.0.2