From bbcbbd567cc15823a6e9d4e2c5899ea3defa7b6d Mon Sep 17 00:00:00 2001
From: Ming Lei <ming.lei@redhat.com>
Date: Wed, 27 Feb 2019 20:40:12 +0800
Subject: block: optimize blk_bio_segment_split for single-page bvec

Introduce a fast path for single-page bvec IO, then we can avoid
to call bvec_split_segs() unnecessarily.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 block/blk-merge.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index c1ad8abbd9d6..9402a7c3ba22 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -286,10 +286,16 @@ new_segment:
 		bvprv = bv;
 		bvprvp = &bvprv;
 
-		if (bvec_split_segs(q, &bv, &nsegs, &seg_size,
-				    &front_seg_size, &sectors))
+		if (bv.bv_offset + bv.bv_len <= PAGE_SIZE) {
+			nsegs++;
+			seg_size = bv.bv_len;
+			sectors += bv.bv_len >> 9;
+			if (nsegs == 1 && seg_size > front_seg_size)
+				front_seg_size = seg_size;
+		} else if (bvec_split_segs(q, &bv, &nsegs, &seg_size,
+				    &front_seg_size, &sectors)) {
 			goto split;
-
+		}
 	}
 
 	do_split = false;
-- 
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