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SubjectRe: [PATCH 1/1] block: rework flush sequencing for blk-mq
On Fri, Mar 14, 2014 at 10:30:53AM +0100, Hannes Reinecke wrote:
> That was actually one of my plans, move dm-multipath over to use
> blk-mq. But then I'd need to discuss with Jens et al how to best
> achieve this; the current static hctx allocation doesn't play well
> with multipaths dynamic path management.

I'd say it the other way around: the clone + insert hacks in
dm-multipath don't work well with blk-mq. Not allowing non-owned
requests is fundamentally part of the blk-mq model to allow things
like the integrated tag allocator and queue depth limiting or the
preallocated driver specific data.

Instead dm-multipath should alway resubmit the request like it already
does for the slow path for the first step. Longer term we might be able
to operate using a cheaper temporary structure, but I'm not sure that's
going to be worth it.


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