This is against the latest git (b922df7383749a1c0b7ea64c50fa839263d3816b). = From: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx> Subject: [PATCH] block: fix nr_phys_segments miscalculation bug This fixes the bug reported by Nikanth Karthikesan <knikanth@xxxxxxx>: http://lkml.org/lkml/2008/10/2/203 The root cause of the bug is that blk_phys_contig_segment miscalculates q->max_segment_size. blk_phys_contig_segment checks: req->biotail->bi_size + next_req->bio->bi_size > q->max_segment_size But blk_recalc_rq_segments might expect that req->biotail and the previous bio in the req are supposed be merged into one segment. blk_recalc_rq_segments might also expect that next_req->bio and the next bio in the next_req are supposed be merged into one segment. In such case, we merge two requests that can't be merged here. Later, blk_rq_map_sg gives more segments than it should. We need to keep track of segment size in blk_recalc_rq_segments and use it to see if two requests can be merged. This patch implements it in the similar way that we used to do for hw merging (virtual merging). Signed-off-by: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx> --- block/blk-merge.c | 20 ++++++++++++++++++-- include/linux/bio.h | 7 +++++++ 2 files changed, 25 insertions(+), 2 deletions(-) diff --git a/block/blk-merge.c b/block/blk-merge.c index 908d3e1..8681cd6 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -77,12 +77,20 @@ void blk_recalc_rq_segments(struct request *rq) continue; } new_segment: + if (nr_phys_segs == 1 && seg_size > rq->bio->bi_seg_front_size) + rq->bio->bi_seg_front_size = seg_size; + nr_phys_segs++; bvprv = bv; seg_size = bv->bv_len; highprv = high; } + if (nr_phys_segs == 1 && seg_size > rq->bio->bi_seg_front_size) + rq->bio->bi_seg_front_size = seg_size; + if (seg_size > rq->biotail->bi_seg_back_size) + rq->biotail->bi_seg_back_size = seg_size; + rq->nr_phys_segments = nr_phys_segs; } @@ -106,7 +114,8 @@ static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio, if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags)) return 0; - if (bio->bi_size + nxt->bi_size > q->max_segment_size) + if (bio->bi_seg_back_size + nxt->bi_seg_front_size > + q->max_segment_size) return 0; if (!bio_has_data(bio)) @@ -309,6 +318,8 @@ static int ll_merge_requests_fn(struct request_queue *q, struct request *req, struct request *next) { int total_phys_segments; + unsigned int seg_size = + req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size; /* * First check if the either of the requests are re-queued @@ -324,8 +335,13 @@ static int ll_merge_requests_fn(struct request_queue *q, struct request *req, return 0; total_phys_segments = req->nr_phys_segments + next->nr_phys_segments; - if (blk_phys_contig_segment(q, req->biotail, next->bio)) + if (blk_phys_contig_segment(q, req->biotail, next->bio)) { + if (req->nr_phys_segments == 1) + req->bio->bi_seg_front_size = seg_size; + if (next->nr_phys_segments == 1) + next->biotail->bi_seg_back_size = seg_size; total_phys_segments--; + } if (total_phys_segments > q->max_phys_segments) return 0; diff --git a/include/linux/bio.h b/include/linux/bio.h index ff5b4cf..dc3cec3 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h @@ -79,6 +79,13 @@ struct bio { unsigned int bi_size; /* residual I/O count */ + /* + * To keep track of the max segment size, we account for the + * sizes of the first and last mergeable segments in this bio. + */ + unsigned int bi_seg_front_size; + unsigned int bi_seg_back_size; + unsigned int bi_max_vecs; /* max bvl_vecs we can hold */ unsigned int bi_comp_cpu; /* completion CPU */ -- 1.5.5.GIT -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
