This is backport of the upstream patch
d12067f428c037b4575aaeb2be00847fc214c24a. It should be backported to
stable kernels because this performance problem was seen on the android
4.4 kernel.
commit d12067f428c037b4575aaeb2be00847fc214c24a
Author: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Date: Wed Nov 23 16:52:01 2016 -0500
dm bufio: don't take the lock in dm_bufio_shrink_count
dm_bufio_shrink_count() is called from do_shrink_slab to find out how many
freeable objects are there. The reported value doesn't have to be precise,
so we don't need to take the dm-bufio lock.
Suggested-by: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
---
drivers/md/dm-bufio.c | 16 ++++------------
1 file changed, 4 insertions(+), 12 deletions(-)
Index: linux-stable/drivers/md/dm-bufio.c
===================================================================
--- linux-stable.orig/drivers/md/dm-bufio.c 2018-07-04 15:25:41.000000000 +0200
+++ linux-stable/drivers/md/dm-bufio.c 2018-07-04 15:33:59.000000000 +0200
@@ -1574,19 +1574,11 @@ dm_bufio_shrink_scan(struct shrinker *sh
static unsigned long
dm_bufio_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
{
- struct dm_bufio_client *c;
- unsigned long count;
- unsigned long retain_target;
+ struct dm_bufio_client *c = container_of(shrink, struct dm_bufio_client, shrinker);
+ unsigned long count = READ_ONCE(c->n_buffers[LIST_CLEAN]) +
+ READ_ONCE(c->n_buffers[LIST_DIRTY]);
+ unsigned long retain_target = get_retain_buffers(c);
- c = container_of(shrink, struct dm_bufio_client, shrinker);
- if (sc->gfp_mask & __GFP_FS)
- dm_bufio_lock(c);
- else if (!dm_bufio_trylock(c))
- return 0;
-
- count = c->n_buffers[LIST_CLEAN] + c->n_buffers[LIST_DIRTY];
- retain_target = get_retain_buffers(c);
- dm_bufio_unlock(c);
return (count < retain_target) ? 0 : (count - retain_target);
}
