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path: root/Documentation/device-mapper/cache-policies.txt
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2016-05-05dm cache: update cache-policies.txt now that mq is an alias for smqMike Snitzer
Also fix some typos and make all "smq" and "mq" references consistently lowercase. Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2016-03-10dm cache: make the 'mq' policy an alias for 'smq'Joe Thornber
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>
2015-06-17dm cache: switch the "default" cache replacement policy from mq to smqMike Snitzer
The Stochastic multiqueue (SMQ) policy (vs MQ) offers the promise of less memory utilization, improved performance and increased adaptability in the face of changing workloads. SMQ also does not have any cumbersome tuning knobs. Users may switch from "mq" to "smq" simply by appropriately reloading a DM table that is using the cache target. Doing so will cause all of the mq policy's hints to be dropped. Also, performance of the cache may degrade slightly until smq recalculates the origin device's hotspots that should be cached. In the future the "mq" policy will just silently make use of "smq" and the mq code will be removed. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Acked-by: Joe Thornber <ejt@redhat.com>
2014-11-10dm cache policy mq: simplify ability to promote sequential IO to the cacheMike Snitzer
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>
2014-11-10dm cache policy mq: tweak algorithm that decides when to promote a blockJoe Thornber
Rather than maintaining a separate promote_threshold variable that we periodically update we now use the hit count of the oldest clean block. Also add a fudge factor to discourage demoting dirty blocks. With some tests this has a sizeable difference, because the old code was too eager to demote blocks. For example, device-mapper-test-suite's git_extract_cache_quick test goes from taking 190 seconds, to 142 (linear on spindle takes 250). Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2014-01-07dm cache policy mq: introduce three promotion threshold tunablesJoe Thornber
Internally the mq policy maintains a promotion threshold variable. If the hit count of a block not in the cache goes above this threshold it gets promoted to the cache. This patch introduces three new tunables that allow you to tweak the promotion threshold by adding a small value. These adjustments depend on the io type: read_promote_adjustment: READ io, default 4 write_promote_adjustment: WRITE io, default 8 discard_promote_adjustment: READ/WRITE io to a discarded block, default 1 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. Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2013-11-09dm cache policy mq: implement writeback_work() and mq_{set,clear}_dirty()Joe Thornber
There are now two multiqueues for in cache blocks. A clean one and a dirty one. writeback_work comes from the dirty one. Demotions come from the clean one. There are two benefits: - Performance improvement, since demoting a clean block is a noop. - The cache cleans itself when io load is light. Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2013-03-01dm cache: add cleaner policyHeinz Mauelshagen
A simple cache policy that writes back all data to the origin. This is used to decommission a dm cache by emptying it. Signed-off-by: Heinz Mauelshagen <mauelshagen@redhat.com> Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2013-03-01dm cache: add mq policyJoe Thornber
A cache policy that uses a multiqueue ordered by recent hit count to select which blocks should be promoted and demoted. This is meant to be a general purpose policy. It prioritises reads over writes. Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>