dm cache policy smq: only demote entries in bottom half of the clean multiqueue

Heavy IO load may mean there are very few clean blocks in the cache, and
we risk demoting entries that get hit a lot.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm-cache-policy-smq.c b/drivers/md/dm-cache-policy-smq.c
index 72479bd61e118e51c4bada036901ebe1bc4b1091..a177559f2049fc24afb2fcf2a92e2ab10d7ebec4 100644 (file)
--- a/drivers/md/dm-cache-policy-smq.c
+++ b/drivers/md/dm-cache-policy-smq.c
@@ -1190,7 +1190,7 @@ static void queue_demotion(struct smq_policy *mq)
        if (unlikely(WARN_ON_ONCE(!mq->migrations_allowed)))
                return;
 
-       e = q_peek(&mq->clean, mq->clean.nr_levels, true);
+       e = q_peek(&mq->clean, mq->clean.nr_levels / 2, true);
        if (!e) {
                if (!clean_target_met(mq, false))
                        queue_writeback(mq);