[3.13.y.z extended stable] Patch "dm bufio: when done scanning return from __scan immediately" has been added to staging queue

Kamal Mostafa kamal at canonical.com
Tue Oct 21 20:09:28 UTC 2014

This is a note to let you know that I have just added a patch titled

    dm bufio: when done scanning return from __scan immediately

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:


This patch is scheduled to be released in version

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see



>From 8256a933326a1f328be4ce384679532bd122db16 Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <mpatocka at redhat.com>
Date: Wed, 1 Oct 2014 13:29:48 -0400
Subject: dm bufio: when done scanning return from __scan immediately

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

Reported-by: Joe Thornber <thornber at redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
Signed-off-by: Mike Snitzer <snitzer at redhat.com>
Signed-off-by: Kamal Mostafa <kamal at 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;

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