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authorJoe Thornber <ejt@redhat.com>2013-11-15 10:51:20 +0000
committerMike Snitzer <snitzer@redhat.com>2013-12-10 16:35:14 -0500
commitaf95e7a69b54bca48092e3013a92cfa3043c9c73 (patch)
tree70f0cf1eff5b7fef29b4656c83b0f57d71f838df /Documentation/device-mapper
parent9b7aaa64f96f7ca280d75326fca42f42017b89ef (diff)
downloadlinux-af95e7a69b54bca48092e3013a92cfa3043c9c73.tar.bz2
dm cache policy mq: fix promotions to occur as expected
Micro benchmarks that repeatedly issued IO to a single block were failing to cause a promotion from the origin device to the cache. Fix this by not updating the stats during map() if -EWOULDBLOCK will be returned. The mq policy will only update stats, consider migration, etc, once per tick period (a unit of time established between dm-cache core and the policies). When the IO thread calls the policy's map method, if it would like to migrate the associated block it returns -EWOULDBLOCK, the IO then gets handed over to a worker thread which handles the migration. The worker thread calls map again, to check the migration is still needed (avoids a race among other things). *BUT*, before this fix, if we were still in the same tick period the stats were already updated by the previous map call -- so the migration would no longer be requested. Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
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