diff options
| author | Joe Thornber <ejt@redhat.com> | 2013-11-15 10:51:20 +0000 |
|---|---|---|
| committer | Mike Snitzer <snitzer@redhat.com> | 2013-12-10 16:35:14 -0500 |
| commit | af95e7a69b54bca48092e3013a92cfa3043c9c73 (patch) | |
| tree | 70f0cf1eff5b7fef29b4656c83b0f57d71f838df | |
| parent | 9b7aaa64f96f7ca280d75326fca42f42017b89ef (diff) | |
| download | linux-af95e7a69b54bca48092e3013a92cfa3043c9c73.tar.bz2 | |
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 <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
| -rw-r--r-- | drivers/md/dm-cache-policy-mq.c | 13 |
1 files 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; } |