From af95e7a69b54bca48092e3013a92cfa3043c9c73 Mon Sep 17 00:00:00 2001 From: Joe Thornber Date: Fri, 15 Nov 2013 10:51:20 +0000 Subject: [PATCH] dm cache policy mq: fix promotions to occur as expected Micro benchmarks that repeatedly issued IO to a single block were failing to cause a promotion from the origin device to the cache. Fix this by not updating the stats during map() if -EWOULDBLOCK will be returned. The mq policy will only update stats, consider migration, etc, once per tick period (a unit of time established between dm-cache core and the policies). When the IO thread calls the policy's map method, if it would like to migrate the associated block it returns -EWOULDBLOCK, the IO then gets handed over to a worker thread which handles the migration. The worker thread calls map again, to check the migration is still needed (avoids a race among other things). *BUT*, before this fix, if we were still in the same tick period the stats were already updated by the previous map call -- so the migration would no longer be requested. Signed-off-by: Joe Thornber Signed-off-by: Mike Snitzer --- drivers/md/dm-cache-policy-mq.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/drivers/md/dm-cache-policy-mq.c b/drivers/md/dm-cache-policy-mq.c index 416b7b752a6e..64780ad73bb0 100644 --- a/drivers/md/dm-cache-policy-mq.c +++ b/drivers/md/dm-cache-policy-mq.c @@ -730,15 +730,18 @@ static int pre_cache_entry_found(struct mq_policy *mq, struct entry *e, int r = 0; bool updated = updated_this_tick(mq, e); - requeue_and_update_tick(mq, e); - if ((!discarded_oblock && updated) || - !should_promote(mq, e, discarded_oblock, data_dir)) + !should_promote(mq, e, discarded_oblock, data_dir)) { + requeue_and_update_tick(mq, e); result->op = POLICY_MISS; - else if (!can_migrate) + + } else if (!can_migrate) r = -EWOULDBLOCK; - else + + else { + requeue_and_update_tick(mq, e); r = pre_cache_to_cache(mq, e, result); + } return r; }