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authorJoe Thornber <ejt@redhat.com>2014-10-22 14:30:58 +0100
committerMike Snitzer <snitzer@redhat.com>2014-11-10 15:25:29 -0500
commitb155aa0e5a81ea1f05ff7aced0ec8e34c980c19e (patch)
tree56f73848b2e70f8a9eb4d97d51b742fc93c3ad0f /Documentation/device-mapper
parent41abc4e1af369bb5438eaee398e3beee690cc8ca (diff)
dm cache policy mq: tweak algorithm that decides when to promote a block
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>
Diffstat (limited to 'Documentation/device-mapper')
-rw-r--r--Documentation/device-mapper/cache-policies.txt6
1 files changed, 3 insertions, 3 deletions
diff --git a/Documentation/device-mapper/cache-policies.txt b/Documentation/device-mapper/cache-policies.txt
index 66c2774c0c64..7746e5dbfd40 100644
--- a/Documentation/device-mapper/cache-policies.txt
+++ b/Documentation/device-mapper/cache-policies.txt
@@ -58,9 +58,9 @@ 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.
-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. The read, write and discard promote adjustment
+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