[PATCH 2/6] block: don't merge adjacent bvecs to one segment in bio blk_queue_split

[Ming Lei <ming.lei@redhat.com>]

For normal filesystem IO, each page is added via blk_add_page(),
in which bvec(page) merge has been handled already, and basically
not possible to merge two adjacent bvecs in one bio.

So not try to merge two adjacent bvecs in blk_queue_split(), also add
check if one page is mergeable to current bvec in bio_add_page() for
avoiding to break XEN.

Cc: ris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: xen-devel@lists.xenproject.org
Cc: Omar Sandoval <osandov@fb.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/bio.c       |  2 ++
 block/blk-merge.c | 17 -----------------
 2 files changed, 2 insertions(+), 17 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 71a78d9fb8b7..d8f48188937c 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -776,6 +776,8 @@ bool __bio_try_merge_page(struct bio *bio, struct page *page,
 
 		if (vec_end_addr + 1 != page_addr + off)
 			return false;
+		if (xen_domain() && !xen_biovec_phys_mergeable(bv, page))
+			return false;
 		if (same_page && (vec_end_addr & PAGE_MASK) != page_addr)
 			return false;
 
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 1c9d4f0f96ea..aa9164eb7187 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -267,23 +267,6 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
 			goto split;
 		}
 
-		if (bvprvp) {
-			if (seg_size + bv.bv_len > queue_max_segment_size(q))
-				goto new_segment;
-			if (!biovec_phys_mergeable(q, bvprvp, &bv))
-				goto new_segment;
-
-			seg_size += bv.bv_len;
-			bvprv = bv;
-			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 == max_segs)
 			goto split;
 
-- 
2.9.5