[dm-devel] [PATCH v3] block, dm: don't copy bios for request clones

[Hannes Reinecke]

On 04/28/2015 02:59 AM, Mike Snitzer wrote:
> From: Christoph Hellwig <hch at lst.de>
> 
> Currently dm-multipath has to clone the bios for every request sent
> to the lower devices, which wastes cpu cycles and ties down memory.
> 
> This patch instead adds a new REQ_CLONE flag that instructs req_bio_endio
> to not complete bios attached to a request, which we set on clone
> requests similar to bios in a flush sequence.  With this change I/O
> errors on a path failure only get propagated to dm-multipath, which
> can then either resubmit the I/O or complete the bios on the original
> request.
> 
> I've done some basic testing of this on a Linux target with ALUA support,
> and it survives path failures during I/O nicely.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> Signed-off-by: Mike Snitzer <snitzer at redhat.com>
Reviewed-by: Hannes Reinecke <hare at suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		               zSeries & Storage
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