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authorChristoph Hellwig <hch@lst.de>2019-05-21 09:01:40 +0200
committerJens Axboe <axboe@kernel.dk>2019-05-23 10:25:26 -0600
commiteded341c085bebdd653f8086c02179098cb81748 (patch)
treea454ef941f258d1d0e7ec4c6bd7d5580d9192e51 /block
parenta0934fd2b1208458e55fc4b48f55889809fce666 (diff)
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block: don't decrement nr_phys_segments for physically contigous segments
Currently ll_merge_requests_fn, unlike all other merge functions, reduces nr_phys_segments by one if the last segment of the previous, and the first segment of the next segement are contigous. While this seems like a nice solution to avoid building smaller than possible requests it causes a mismatch between the segments actually present in the request and those iterated over by the bvec iterators, including __rq_for_each_bio. This can for example mistrigger the single segment optimization in the nvme-pci driver, and might lead to mismatching nr_phys_segments number when recalculating the number of request when inserting a cloned request. We could possibly work around this by making the bvec iterators take the front and back segment size into account, but that would require moving them from the bio to the bio_iter and spreading this mess over all users of bvecs. Or we could simply remove this optimization under the assumption that most users already build good enough bvecs, and that the bio merge patch never cared about this optimization either. The latter is what this patch does. dff824b2aadb ("nvme-pci: optimize mapping of small single segment requests"). Reviewed-by: Ming Lei <ming.lei@redhat.com> Reviewed-by: Hannes Reinecke <hare@suse.com> Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
-rw-r--r--block/blk-merge.c23
1 files changed, 1 insertions, 22 deletions
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 21e87a714a73..80a5a0facb87 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -358,7 +358,6 @@ static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
unsigned front_seg_size;
struct bio *fbio, *bbio;
struct bvec_iter iter;
- bool new_bio = false;
if (!bio)
return 0;
@@ -379,31 +378,12 @@ static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
nr_phys_segs = 0;
for_each_bio(bio) {
bio_for_each_bvec(bv, bio, iter) {
- if (new_bio) {
- if (seg_size + bv.bv_len
- > queue_max_segment_size(q))
- goto new_segment;
- if (!biovec_phys_mergeable(q, &bvprv, &bv))
- goto new_segment;
-
- seg_size += bv.bv_len;
-
- if (nr_phys_segs == 1 && seg_size >
- front_seg_size)
- front_seg_size = seg_size;
-
- continue;
- }
-new_segment:
bvec_split_segs(q, &bv, &nr_phys_segs, &seg_size,
&front_seg_size, NULL, UINT_MAX);
- new_bio = false;
}
bbio = bio;
- if (likely(bio->bi_iter.bi_size)) {
+ if (likely(bio->bi_iter.bi_size))
bvprv = bv;
- new_bio = true;
- }
}
fbio->bi_seg_front_size = front_seg_size;
@@ -725,7 +705,6 @@ static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
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 > queue_max_segments(q))