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Joe Thornber authored
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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