[PATCH 3.13 075/105] dm bufio: when done scanning return from __scan immediately

Kamal Mostafa
2014-10-27T19:06:52Z

From: Mikulas Patocka <mpatocka@redhat.com>

commit 0e825862f3c04cee40e25f55680333728a4ffa9b upstream.

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>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
drivers/md/dm-bufio.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index bb8d23d..a42efc7 100644
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -1456,9 +1456,9 @@ 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;
}
--
1.9.1