On 05/22/15 22:14, Mike Snitzer wrote: > From: Christoph Hellwig <hch@xxxxxx> > > 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. .. > @@ -128,7 +128,8 @@ static void req_bio_endio(struct request *rq, struct bio *bio, > bio_advance(bio, nbytes); > > /* don't actually finish bio if it's part of flush sequence */ > - if (bio->bi_iter.bi_size == 0 && !(rq->cmd_flags & REQ_FLUSH_SEQ)) > + if (bio->bi_iter.bi_size == 0 && > + !(rq->cmd_flags & (REQ_FLUSH_SEQ|REQ_CLONE))) > bio_endio(bio, error); > } Not completing bios is not sufficient. If you advance the bi_iter to the end, you need to somehow rewind it or the re-submission will be incomplete, that would end up as a data corruption... -- Jun'ichi Nomura, NEC Corporation -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
