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author | Joe Thornber <ejt@redhat.com> | 2016-02-10 10:18:10 +0000 |
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committer | Mike Snitzer <snitzer@redhat.com> | 2016-03-10 17:12:08 -0500 |
commit | 9ed84698fdda63de93c68150c4f63673cc3d7b54 (patch) | |
tree | 3722d66694317bf32b99444fd31a52ec7e5825ed /Documentation | |
parent | e233d800a9648f2c0802aa23250d9c8af57bab43 (diff) | |
download | linux-9ed84698fdda63de93c68150c4f63673cc3d7b54.tar.gz linux-9ed84698fdda63de93c68150c4f63673cc3d7b54.tar.bz2 linux-9ed84698fdda63de93c68150c4f63673cc3d7b54.zip |
dm cache: make the 'mq' policy an alias for 'smq'
smq seems to be performing better than the old mq policy in all
situations, as well as using a quarter of the memory.
Make 'mq' an alias for 'smq' when choosing a cache policy. The tunables
that were present for the old mq are faked, and have no effect. mq
should be considered deprecated now.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/device-mapper/cache-policies.txt | 39 |
1 files changed, 2 insertions, 37 deletions
diff --git a/Documentation/device-mapper/cache-policies.txt b/Documentation/device-mapper/cache-policies.txt index d9246a32e673..e5062ad18717 100644 --- a/Documentation/device-mapper/cache-policies.txt +++ b/Documentation/device-mapper/cache-policies.txt @@ -28,51 +28,16 @@ Overview of supplied cache replacement policies multiqueue (mq) --------------- -This policy has been deprecated in favor of the smq policy (see below). +This policy is now an alias for smq (see below). -The multiqueue policy has three sets of 16 queues: one set for entries -waiting for the cache and another two for those in the cache (a set for -clean entries and a set for dirty entries). +The following tunables are accepted, but have no effect: -Cache entries in the queues are aged based on logical time. Entry into -the cache is based on variable thresholds and queue selection is based -on hit count on entry. The policy aims to take different cache miss -costs into account and to adjust to varying load patterns automatically. - -Message and constructor argument pairs are: 'sequential_threshold <#nr_sequential_ios>' 'random_threshold <#nr_random_ios>' 'read_promote_adjustment <value>' 'write_promote_adjustment <value>' 'discard_promote_adjustment <value>' -The sequential threshold indicates the number of contiguous I/Os -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 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 -promoted to the cache. The read, write and discard promote adjustment -tunables allow you to tweak the promotion threshold by adding a small -value based on the io type. They default to 4, 8 and 1 respectively. -If you're trying to quickly warm a new cache device you may wish to -reduce these to encourage promotion. Remember to switch them back to -their defaults after the cache fills though. - Stochastic multiqueue (smq) --------------------------- |