[3.11.y.z extended stable] Patch "dm thin: avoid metadata commit if a pool's thin devices haven't" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    dm thin: avoid metadata commit if a pool's thin devices haven't

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 7c3cd620dae7958394c2aa842e4b920c43462c1e Mon Sep 17 00:00:00 2001
From: Mike Snitzer <snitzer at redhat.com>
Date: Thu, 6 Feb 2014 06:08:56 -0500
Subject: dm thin: avoid metadata commit if a pool's thin devices haven't
 changed

commit 4d1662a30dde6e545086fe0e8fd7e474c4e0b639 upstream.

Commit 905e51b ("dm thin: commit outstanding data every second")
introduced a periodic commit.  This commit occurs regardless of whether
any thin devices have made changes.

Fix the periodic commit to check if any of a pool's thin devices have
changed using dm_pool_changed_this_transaction().

Reported-by: Alexander Larsson <alexl at redhat.com>
Signed-off-by: Mike Snitzer <snitzer at redhat.com>
Acked-by: Joe Thornber <ejt at redhat.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/md/dm-thin-metadata.c | 17 +++++++++++++++++
 drivers/md/dm-thin-metadata.h |  2 ++
 drivers/md/dm-thin.c          |  3 ++-
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm-thin-metadata.c b/drivers/md/dm-thin-metadata.c
index 7da3476..3bb4506 100644
--- a/drivers/md/dm-thin-metadata.c
+++ b/drivers/md/dm-thin-metadata.c
@@ -1489,6 +1489,23 @@ bool dm_thin_changed_this_transaction(struct dm_thin_device *td)
 	return r;
 }

+bool dm_pool_changed_this_transaction(struct dm_pool_metadata *pmd)
+{
+	bool r = false;
+	struct dm_thin_device *td, *tmp;
+
+	down_read(&pmd->root_lock);
+	list_for_each_entry_safe(td, tmp, &pmd->thin_devices, list) {
+		if (td->changed) {
+			r = td->changed;
+			break;
+		}
+	}
+	up_read(&pmd->root_lock);
+
+	return r;
+}
+
 bool dm_thin_aborted_changes(struct dm_thin_device *td)
 {
 	bool r;
diff --git a/drivers/md/dm-thin-metadata.h b/drivers/md/dm-thin-metadata.h
index 2edf5db..c6d123b 100644
--- a/drivers/md/dm-thin-metadata.h
+++ b/drivers/md/dm-thin-metadata.h
@@ -161,6 +161,8 @@ int dm_thin_remove_block(struct dm_thin_device *td, dm_block_t block);
  */
 bool dm_thin_changed_this_transaction(struct dm_thin_device *td);

+bool dm_pool_changed_this_transaction(struct dm_pool_metadata *pmd);
+
 bool dm_thin_aborted_changes(struct dm_thin_device *td);

 int dm_thin_get_highest_mapped_block(struct dm_thin_device *td,
diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 0a9b087..9189838 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -1346,7 +1346,8 @@ static void process_deferred_bios(struct pool *pool)
 	bio_list_init(&pool->deferred_flush_bios);
 	spin_unlock_irqrestore(&pool->lock, flags);

-	if (bio_list_empty(&bios) && !need_commit_due_to_time(pool))
+	if (bio_list_empty(&bios) &&
+	    !(dm_pool_changed_this_transaction(pool->pmd) && need_commit_due_to_time(pool)))
 		return;

 	if (commit(pool)) {
--
1.9.0