From b155aa0e5a81ea1f05ff7aced0ec8e34c980c19e Mon Sep 17 00:00:00 2001 From: Joe Thornber Date: Wed, 22 Oct 2014 14:30:58 +0100 Subject: 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 Signed-off-by: Mike Snitzer --- Documentation/device-mapper/cache-policies.txt | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'Documentation/device-mapper') 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 -- cgit v1.2.3