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block, dm: don't copy bios for request clones

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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@lst.de>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Christoph Hellwig
2015-05-22 09:14:04 -04:00
committed by Jens Axboe
parent 326e1dbb57
commit 5f1b670d0b
6 changed files with 73 additions and 230 deletions
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6
include/linux/blkdev.h
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@@ -775,11 +775,7 @@ extern void blk_add_request_payload(struct request *rq, struct page *page,
unsigned int len);
extern int blk_rq_check_limits(struct request_queue *q, struct request *rq);
extern int blk_lld_busy(struct request_queue *q);
extern int blk_rq_prep_clone(struct request *rq, struct request *rq_src,
struct bio_set *bs, gfp_t gfp_mask,
int (*bio_ctr)(struct bio *, struct bio *, void *),
void *data);
extern void blk_rq_unprep_clone(struct request *rq);
extern void blk_rq_prep_clone(struct request *rq, struct request *rq_src);
extern int blk_insert_cloned_request(struct request_queue *q,
struct request *rq);
extern void blk_delay_queue(struct request_queue *, unsigned long);