[PATCH V4 12/45] blk-merge: compute bio->bi_seg_front_size efficiently

Ming Lei
2017-12-18T12:26:02Z

It is enough to check and compute bio->bi_seg_front_size just
after the 1st segment is found, but current code checks that
for each bvec, which is inefficient.

This patch follows the way in __blk_recalc_rq_segments()
for computing bio->bi_seg_front_size, and it is more efficient
and code becomes more readable too.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
block/blk-merge.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index f5dedd57dff6..a476337a8ff4 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -146,22 +146,21 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
bvprvp = &bvprv;
sectors += bv.bv_len >> 9;

- if (nsegs == 1 && seg_size > front_seg_size)
- front_seg_size = seg_size;
continue;
}
new_segment:
if (nsegs == queue_max_segments(q))
goto split;

+ if (nsegs == 1 && seg_size > front_seg_size)
+ front_seg_size = seg_size;
+
nsegs++;
bvprv = bv;
bvprvp = &bvprv;
seg_size = bv.bv_len;
sectors += bv.bv_len >> 9;

- if (nsegs == 1 && seg_size > front_seg_size)
- front_seg_size = seg_size;
}

do_split = false;
@@ -174,6 +173,8 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
bio = new;
}

+ if (nsegs == 1 && seg_size > front_seg_size)
+ front_seg_size = seg_size;
bio->bi_seg_front_size = front_seg_size;
if (seg_size > bio->bi_seg_back_size)
bio->bi_seg_back_size = seg_size;
--
2.9.5