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

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@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Acked-by: Joe Thornber <ejt@redhat.com>
Cc: stable@vger.kernel.org

3 files changed, 21 insertions, 1 deletions

diff --git a/drivers/md/dm-thin-metadata.c b/drivers/md/dm-thin-metadata.c
index 7da347665552..3bb4506582a9 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 9a368567632f..dd6088a17a65 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 faaf944597ab..d501e436a7d9 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -1357,7 +1357,8 @@ 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)) {