diff options
| author | Mike Snitzer | 2014-10-30 10:02:01 -0400 |
|---|---|---|
| committer | Mike Snitzer | 2014-11-10 15:25:30 -0500 |
| commit | f1afb36a6102b52949c2c6d8eb250eddcce3fc5f (patch) | |
| tree | f8e7143d1118635d88c6989ebb80654c109756f9 | |
| parent | b155aa0e5a81ea1f05ff7aced0ec8e34c980c19e (diff) | |
dm cache policy mq: simplify ability to promote sequential IO to the cache
Before, if the user wanted sequential IO to be promoted to the cache
they'd have to set sequential_threshold to some nebulous large value.
Now, the user may easily disable sequential IO detection (and sequential
IO's implicit bypass of the cache) by setting sequential_threshold to 0.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
| -rw-r--r-- | Documentation/device-mapper/cache-policies.txt | 16 | ||||
| -rw-r--r-- | drivers/md/dm-cache-policy-mq.c | 7 |
2 files changed, 15 insertions, 8 deletions
diff --git a/Documentation/device-mapper/cache-policies.txt b/Documentation/device-mapper/cache-policies.txt index 7746e5dbfd40..0d124a971801 100644 --- a/Documentation/device-mapper/cache-policies.txt +++ b/Documentation/device-mapper/cache-policies.txt @@ -47,16 +47,22 @@ Message and constructor argument pairs are: 'discard_promote_adjustment <value>' The sequential threshold indicates the number of contiguous I/Os -required before a stream is treated as sequential. The random threshold +required before a stream is treated as sequential. Once a stream is +considered sequential it will bypass the cache. The random threshold is the number of intervening non-contiguous I/Os that must be seen before the stream is treated as random again. The sequential and random thresholds default to 512 and 4 respectively. -Large, sequential ios are probably better left on the origin device -since spindles tend to have good bandwidth. The io_tracker counts -contiguous I/Os to try to spot when the io is in one of these sequential -modes. +Large, sequential I/Os are probably better left on the origin device +since spindles tend to have good sequential I/O bandwidth. The +io_tracker counts contiguous I/Os to try to spot when the I/O is in one +of these sequential modes. But there are use-cases for wanting to +promote sequential blocks to the cache (e.g. fast application startup). +If sequential threshold is set to 0 the sequential I/O detection is +disabled and sequential I/O will no longer implicitly bypass the cache. +Setting the random threshold to 0 does _not_ disable the random I/O +stream detection. Internally the mq policy determines a promotion threshold. If the hit count of a block not in the cache goes above this threshold it gets diff --git a/drivers/md/dm-cache-policy-mq.c b/drivers/md/dm-cache-policy-mq.c index 334d098d720d..13f547a4eeb6 100644 --- a/drivers/md/dm-cache-policy-mq.c +++ b/drivers/md/dm-cache-policy-mq.c @@ -865,7 +865,8 @@ static int map(struct mq_policy *mq, dm_oblock_t oblock, if (e && in_cache(mq, e)) r = cache_entry_found(mq, e, result); - else if (iot_pattern(&mq->tracker) == PATTERN_SEQUENTIAL) + else if (mq->tracker.thresholds[PATTERN_SEQUENTIAL] && + iot_pattern(&mq->tracker) == PATTERN_SEQUENTIAL) result->op = POLICY_MISS; else if (e) @@ -1290,7 +1291,7 @@ bad_pre_cache_init: static struct dm_cache_policy_type mq_policy_type = { .name = "mq", - .version = {1, 2, 0}, + .version = {1, 3, 0}, .hint_size = 4, .owner = THIS_MODULE, .create = mq_create @@ -1298,7 +1299,7 @@ static struct dm_cache_policy_type mq_policy_type = { static struct dm_cache_policy_type default_policy_type = { .name = "default", - .version = {1, 2, 0}, + .version = {1, 3, 0}, .hint_size = 4, .owner = THIS_MODULE, .create = mq_create, |