dm thin: avoid unnecessarily breaking sharing for flushes
There's no need to break sharing, triggering a copy, for a write that has no
data (i.e. a flush).
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 423df92..7510cb3 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -1315,7 +1315,7 @@
if (bio_detain(pool->prison, &key, bio, &cell))
return;
- if (bio_data_dir(bio) == WRITE)
+ if (bio_data_dir(bio) == WRITE && bio->bi_size)
break_sharing(tc, bio, block, &key, lookup_result, cell);
else {
struct dm_thin_endio_hook *h = dm_get_mapinfo(bio)->ptr;