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block: optimize __blk_segment_map_sg() for single-page bvec

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Introduce a fast path for single-page bvec IO, then blk_bvec_map_sg()
can be avoided.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2019-02-27 20:40:11 +08:00 committed by Jens Axboe
parent 4d633062c1
commit 48d7727cae
1 changed files with 7 additions and 2 deletions
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9
block/blk-merge.c
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@ -447,7 +447,7 @@ static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
return biovec_phys_mergeable(q, &end_bv, &nxt_bv); return biovec_phys_mergeable(q, &end_bv, &nxt_bv);
} }
static struct scatterlist *blk_next_sg(struct scatterlist **sg, static inline struct scatterlist *blk_next_sg(struct scatterlist **sg,
struct scatterlist *sglist) struct scatterlist *sglist)
{ {
if (!*sg) if (!*sg)
@ -512,7 +512,12 @@ __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
(*sg)->length += nbytes; (*sg)->length += nbytes;
} else { } else {
new_segment: new_segment:
(*nsegs) += blk_bvec_map_sg(q, bvec, sglist, sg); if (bvec->bv_offset + bvec->bv_len <= PAGE_SIZE) {
*sg = blk_next_sg(sg, sglist);
sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
(*nsegs) += 1;
} else
(*nsegs) += blk_bvec_map_sg(q, bvec, sglist, sg);
} }
*bvprv = *bvec; *bvprv = *bvec;
} }