dm bufio: when done scanning return from __scan immediately

When __scan frees the required number of buffer entries that the
shrinker requested (nr_to_scan becomes zero) it must return.  Before
this fix the __scan code exited only the inner loop and continued in the
outer loop -- which could result in reduced performance due to extra
buffers being freed (e.g. unnecessarily evicted thinp metadata needing
to be synchronously re-read into bufio's cache).

Also, move dm_bufio_cond_resched to __scan's inner loop, so that
iterating the bufio client's lru lists doesn't result in scheduling
latency.

Reported-by: Joe Thornber <thornber@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org # 3.2+

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index eab64bcaab66..9ea5b6041eb2 100644
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -1473,9 +1473,9 @@ static long __scan(struct dm_bufio_client *c, unsigned long nr_to_scan,
                 list_for_each_entry_safe_reverse(b, tmp, &c->lru[l], lru_list) {
                         freed += __cleanup_old_buffer(b, gfp_mask, 0);
                         if (!--nr_to_scan)
-                                break;
+                                return freed;
+                        dm_bufio_cond_resched();
                 }
-                dm_bufio_cond_resched();
         }
         return freed;
 }