Messages in this thread | | | Date | Fri, 10 May 2013 11:22:24 +0100 | From | Joe Thornber <> | Subject | Re: [dm-devel] [PATCH 2/2] dmcache: Implement a flush message |
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On Thu, May 09, 2013 at 01:47:51PM -0700, Darrick J. Wong wrote: > Create a new 'flush' message that causes the dmcache to write all of its > metadata out to disk. This enables us to ensure that the disk reflects > whatever's in memory without having to tear down the cache device. This helps > me in the case where I have a cached ro fs that I can't umount and therefore > can't tear down the cache device, but want to save the cache metadata anyway. > The command syntax is as follows: > > # dmsetup message mycache 0 flush now
Nack.
[Ignoring the ugly 'now' parameter.]
I think you're in danger of hiding the real issue. Which is if the target's destructor and post suspend is not being called then, as far as dm-cache is concerned this is a crash. Any open transactions will be lost as it automatically rolls back.
We need to understand more why this is happening. It's actually harmless atm for dm-cache, because we're forced to commit before using a new migration. But for dm-thin you can lose writes. Why are you never tearing down your dm devices?
- Joe
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