dm bufio: update last_accessed when relinking a buffer

commit eb76faf53b1ff7a77ce3f78cc98ad392ac70c2a0 upstream.

The 'last_accessed' member of the dm_buffer structure was only set when
the the buffer was created.  This led to each buffer being discarded
after dm_bufio_max_age time even if it was used recently.  In practice
this resulted in all thinp metadata being evicted soon after being read
-- this is particularly problematic for metadata intensive workloads
like multithreaded small random IO.

'last_accessed' is now updated each time the buffer is moved to the head
of the LRU list, so the buffer is now properly discarded if it was not
used in dm_bufio_max_age time.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index 910d2f8..8abd681 100644 (file)
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -468,6 +468,7 @@ static void __relink_lru(struct dm_buffer *b, int dirty)
        b->list_mode = dirty;
        list_del(&b->lru_list);
        list_add(&b->lru_list, &c->lru[dirty]);
        b->list_mode = dirty;
        list_del(&b->lru_list);
        list_add(&b->lru_list, &c->lru[dirty]);

+       b->last_accessed = jiffies;

 }
 
 /*----------------------------------------------------------------
 }
 
 /*----------------------------------------------------------------