From 5f60ae1d686f025445fdf09f546d4d055d255ce9 Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Fri, 18 Mar 2016 12:41:53 +0800 Subject: [PATCH] block: loose check on sg gap If the last bvec of the 1st bio and the 1st bvec of the next bio are contineous physically, and the latter can be merged to last segment of the 1st bio, we should think they don't violate sg gap(or virt boundary) limit. Vitaly reported lots of unmergeable small bios are observed when running mkfs.ntfs on Hyper-V virtual storage, and performance becomes quite low, so this patch is figured out for fix the performance issue. Reported-by: Vitaly Kuznetsov Cc: Keith Busch Signed-off-by: Ming Lei --- include/linux/blkdev.h | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-) diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 7e5d7e0..3962527 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -1394,6 +1394,25 @@ static inline bool bvec_gap_to_prev(struct request_queue *q, return __bvec_gap_to_prev(q, bprv, offset); } +/* + * Check if the two bvecs from two bios can be merged to one segment. + * If yes, no need to check gap between the two bios since the 1st bio + * and the 1st bvec in the 2nd bio can be handled in one segment. + */ +static inline bool bios_segs_mergeable(struct request_queue *q, + struct bio *prev, struct bio_vec *prev_last_bv, + struct bio_vec *next_first_bv) +{ + if (!BIOVEC_PHYS_MERGEABLE(prev_last_bv, next_first_bv)) + return false; + if (!BIOVEC_SEG_BOUNDARY(q, prev_last_bv, next_first_bv)) + return false; + if (prev->bi_seg_back_size + next_first_bv->bv_len > + queue_max_segment_size(q)) + return false; + return true; +} + static inline bool bio_will_gap(struct request_queue *q, struct bio *prev, struct bio *next) { @@ -1403,7 +1422,8 @@ static inline bool bio_will_gap(struct request_queue *q, struct bio *prev, bio_get_last_bvec(prev, &pb); bio_get_first_bvec(next, &nb); - return __bvec_gap_to_prev(q, &pb, nb.bv_offset); + if (!bios_segs_mergeable(q, prev, &pb, &nb)) + return __bvec_gap_to_prev(q, &pb, nb.bv_offset); } return false; -- 1.9.1