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 (file)
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -1315,7 +1315,7 @@ static void process_shared_bio(struct thin_c *tc, struct bio *bio,
        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;