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dm cache policy mq: implement writeback_work() and mq_{set,clear}_dirty()

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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>
This commit is contained in:
Joe Thornber
2013-10-24 14:10:28 -04:00
committed by Mike Snitzer
parent ffcbcb6720
commit 01911c19be
2 changed files with 132 additions and 21 deletions
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Documentation/device-mapper/cache-policies.txt
+4 -2
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@@ -30,8 +30,10 @@ multiqueue
This policy is the default.
The multiqueue policy has two sets of 16 queues: one set for entries
waiting for the cache and another one for those in the cache.
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).
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