This is a note to let you know that I've just added the patch titled
dm-snapshot: fix performance degradation due to small hash size
to the 3.11-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
dm-snapshot-fix-performance-degradation-due-to-small-hash-size.patch
and it can be found in the queue-3.11 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 60e356f381954d79088d0455e357db48cfdd6857 Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Date: Wed, 18 Sep 2013 19:40:42 -0400
Subject: dm-snapshot: fix performance degradation due to small hash size
From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
commit 60e356f381954d79088d0455e357db48cfdd6857 upstream.
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 <mpatocka@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/md/dm-snap.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
--- 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)
Patches currently in stable-queue which might be from mpatocka@xxxxxxxxxx are
queue-3.11/dm-snapshot-fix-performance-degradation-due-to-small-hash-size.patch
queue-3.11/dm-snapshot-workaround-for-a-false-positive-lockdep-warning.patch
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