From 60e356f381954d79088d0455e357db48cfdd6857 Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Wed, 18 Sep 2013 19:40:42 -0400 Subject: [PATCH] dm-snapshot: fix performance degradation due to small hash size LVM2, since version 2.02.96, creates origin with zero size, then loads the snapshot driver and then loads the origin. Consequently, the snapshot driver sees the origin size zero and sets the hash size to the lower bound 64. Such small hash table causes performance degradation. This patch changes it so that the hash size is determined by the size of snapshot volume, not minimum of origin and snapshot size. It doesn't make sense to set the snapshot size significantly larger than the origin size, so we do not need to take origin size into account when calculating the hash size. Signed-off-by: Mikulas Patocka Signed-off-by: Mike Snitzer Cc: stable@vger.kernel.org --- drivers/md/dm-snap.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c index c434e5aab2df..aec57d76db5d 100644 --- a/drivers/md/dm-snap.c +++ b/drivers/md/dm-snap.c @@ -725,17 +725,16 @@ static int calc_max_buckets(void) */ static int init_hash_tables(struct dm_snapshot *s) { - sector_t hash_size, cow_dev_size, origin_dev_size, max_buckets; + sector_t hash_size, cow_dev_size, max_buckets; /* * Calculate based on the size of the original volume or * the COW volume... */ cow_dev_size = get_dev_size(s->cow->bdev); - origin_dev_size = get_dev_size(s->origin->bdev); max_buckets = calc_max_buckets(); - hash_size = min(origin_dev_size, cow_dev_size) >> s->store->chunk_shift; + hash_size = cow_dev_size >> s->store->chunk_shift; hash_size = min(hash_size, max_buckets); if (hash_size < 64) -- 2.20.1