[dm-devel] dm-cache selective promotion of block
Mike Snitzer
snitzer at redhat.com
Thu Dec 17 21:18:06 UTC 2015
On Thu, Dec 17 2015 at 2:11pm -0500,
Mahmoud Hanafi <mahmoud.hanafi at nasa.gov> wrote:
> We are experimenting with dm-cache and would like to be able to
> promote a range of block and pin them in the cache device.
>
> Are there any tool that can be used for this?
There isn't an interface to do that right now. But it _should_ be
possible to add a DM message to easily promote an origin block range.
Pinning isn't something we really do at this point so that'd require
more work.
But it could look something like this:
dmsetup message <cache_dev> 0 promote_oblocks <start> <end>
dmsetup message <cache_dev> 0 pin_oblocks <start> <end>
and:
dmsetup message <cache_dev> 0 demote_oblocks <start> <end>
dmsetup message <cache_dev> 0 unpin_oblocks <start> <end>
(where <start> and <end> are in either cache_block_size units or 512b
sectors... not sure which would be best, sectors is a bit more
approachable)
I could see this getting a bit cumbersome, not to mention the smq cache
policy really _should_ promote if it makes sense to cache a block, but
we'll certainly need Joe's thoughts on this.
Mike
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