Commit 8677142710516d986d932d6f1fba7be8382c1fec
Committed by
Jens Axboe
Jens Axboe
1 parent
0fc71e3d65
Exists in
master
and in
7 other branches
block: fix nr_phys_segments miscalculation bug
This fixes the bug reported by Nikanth Karthikesan <knikanth@suse.de>: 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@lab.ntt.co.jp> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Showing 2 changed files with 25 additions and 2 deletions Side-by-side Diff
block/blk-merge.c
| ... | ... | @@ -77,12 +77,20 @@ |
| 77 | 77 | continue; |
| 78 | 78 | } |
| 79 | 79 | new_segment: |
| 80 | + if (nr_phys_segs == 1 && seg_size > rq->bio->bi_seg_front_size) | |
| 81 | + rq->bio->bi_seg_front_size = seg_size; | |
| 82 | + | |
| 80 | 83 | nr_phys_segs++; |
| 81 | 84 | bvprv = bv; |
| 82 | 85 | seg_size = bv->bv_len; |
| 83 | 86 | highprv = high; |
| 84 | 87 | } |
| 85 | 88 | |
| 89 | + if (nr_phys_segs == 1 && seg_size > rq->bio->bi_seg_front_size) | |
| 90 | + rq->bio->bi_seg_front_size = seg_size; | |
| 91 | + if (seg_size > rq->biotail->bi_seg_back_size) | |
| 92 | + rq->biotail->bi_seg_back_size = seg_size; | |
| 93 | + | |
| 86 | 94 | rq->nr_phys_segments = nr_phys_segs; |
| 87 | 95 | } |
| 88 | 96 | |
| ... | ... | @@ -106,7 +114,8 @@ |
| 106 | 114 | if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags)) |
| 107 | 115 | return 0; |
| 108 | 116 | |
| 109 | - if (bio->bi_size + nxt->bi_size > q->max_segment_size) | |
| 117 | + if (bio->bi_seg_back_size + nxt->bi_seg_front_size > | |
| 118 | + q->max_segment_size) | |
| 110 | 119 | return 0; |
| 111 | 120 | |
| 112 | 121 | if (!bio_has_data(bio)) |
| ... | ... | @@ -309,6 +318,8 @@ |
| 309 | 318 | struct request *next) |
| 310 | 319 | { |
| 311 | 320 | int total_phys_segments; |
| 321 | + unsigned int seg_size = | |
| 322 | + req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size; | |
| 312 | 323 | |
| 313 | 324 | /* |
| 314 | 325 | * First check if the either of the requests are re-queued |
| 315 | 326 | |
| ... | ... | @@ -324,8 +335,13 @@ |
| 324 | 335 | return 0; |
| 325 | 336 | |
| 326 | 337 | total_phys_segments = req->nr_phys_segments + next->nr_phys_segments; |
| 327 | - if (blk_phys_contig_segment(q, req->biotail, next->bio)) | |
| 338 | + if (blk_phys_contig_segment(q, req->biotail, next->bio)) { | |
| 339 | + if (req->nr_phys_segments == 1) | |
| 340 | + req->bio->bi_seg_front_size = seg_size; | |
| 341 | + if (next->nr_phys_segments == 1) | |
| 342 | + next->biotail->bi_seg_back_size = seg_size; | |
| 328 | 343 | total_phys_segments--; |
| 344 | + } | |
| 329 | 345 | |
| 330 | 346 | if (total_phys_segments > q->max_phys_segments) |
| 331 | 347 | return 0; |
include/linux/bio.h
| ... | ... | @@ -79,6 +79,13 @@ |
| 79 | 79 | |
| 80 | 80 | unsigned int bi_size; /* residual I/O count */ |
| 81 | 81 | |
| 82 | + /* | |
| 83 | + * To keep track of the max segment size, we account for the | |
| 84 | + * sizes of the first and last mergeable segments in this bio. | |
| 85 | + */ | |
| 86 | + unsigned int bi_seg_front_size; | |
| 87 | + unsigned int bi_seg_back_size; | |
| 88 | + | |
| 82 | 89 | unsigned int bi_max_vecs; /* max bvl_vecs we can hold */ |
| 83 | 90 | |
| 84 | 91 | unsigned int bi_comp_cpu; /* completion CPU */ |