| Message ID | 20170807124330.10698-1-f.gruenbichler@proxmox.com |
|---|---|
| State | New |
| Headers | show |
On Mon, Aug 07, 2017 at 02:43:30PM +0200, Fabian Grünbichler wrote: > From: Ming Lei <ming.lei@redhat.com> > > BugLink: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1709073 > > Commit 729204ef49ec("block: relax check on sg gap") allows us to merge > bios, if both are physically contiguous. This change can merge a huge > number of small bios, through mkfs for example, mkfs.ntfs running time > can be decreased to ~1/10. > > But if one rq starts with a non-aligned buffer (the 1st bvec's bv_offset > is non-zero) and if we allow the merge, it is quite difficult to respect > sg gap limit, especially the max segment size, or we risk having an > unaligned virtual boundary. This patch tries to avoid the issue by > disallowing a merge, if the req starts with an unaligned buffer. > > Also add comments to explain why the merged segment can't end in > unaligned virt boundary. > > Fixes: 729204ef49ec ("block: relax check on sg gap") > Tested-by: Johannes Thumshirn <jthumshirn@suse.de> > Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de> > Signed-off-by: Ming Lei <ming.lei@redhat.com> > > Rewrote parts of the commit message and comments. > > Signed-off-by: Jens Axboe <axboe@fb.com> > (cherry picked from commit 5a8d75a1b8c99bdc926ba69b7b7dbe4fae81a5af) > Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com> Clean upstream cherry pick, looks reasonable. Acked-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
Applied to zesty/master-next branch fixing the BugLink to the format "http://bugs.launchpad.net/bugs/<bug-id>". Thanks.
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index e36a23d0ae31..758ff0e75cce 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -1639,12 +1639,36 @@ static inline bool bios_segs_mergeable(struct request_queue *q, return true; } -static inline bool bio_will_gap(struct request_queue *q, struct bio *prev, - struct bio *next) +static inline bool bio_will_gap(struct request_queue *q, + struct request *prev_rq, + struct bio *prev, + struct bio *next) { if (bio_has_data(prev) && queue_virt_boundary(q)) { struct bio_vec pb, nb; + /* + * don't merge if the 1st bio starts with non-zero + * offset, otherwise it is quite difficult to respect + * sg gap limit. We work hard to merge a huge number of small + * single bios in case of mkfs. + */ + if (prev_rq) + bio_get_first_bvec(prev_rq->bio, &pb); + else + bio_get_first_bvec(prev, &pb); + if (pb.bv_offset) + return true; + + /* + * We don't need to worry about the situation that the + * merged segment ends in unaligned virt boundary: + * + * - if 'pb' ends aligned, the merged segment ends aligned + * - if 'pb' ends unaligned, the next bio must include + * one single bvec of 'nb', otherwise the 'nb' can't + * merge with 'pb' + */ bio_get_last_bvec(prev, &pb); bio_get_first_bvec(next, &nb); @@ -1657,12 +1681,12 @@ static inline bool bio_will_gap(struct request_queue *q, struct bio *prev, static inline bool req_gap_back_merge(struct request *req, struct bio *bio) { - return bio_will_gap(req->q, req->biotail, bio); + return bio_will_gap(req->q, req, req->biotail, bio); } static inline bool req_gap_front_merge(struct request *req, struct bio *bio) { - return bio_will_gap(req->q, bio, req->bio); + return bio_will_gap(req->q, NULL, bio, req->bio); } int kblockd_schedule_work(struct work_struct *work);