dm bufio: don't take the lock in dm_bufio_shrink_count

commit d12067f428c037b4575aaeb2be00847fc214c24a upstream.

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@google.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index 57b01bc..c837def 100644 (file)
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -1598,19 +1598,11 @@ dm_bufio_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
 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;
-
-       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;
+       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);
 
-       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);
 }