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

[Ming Lei <ming.lei@xxxxxxxxxx>]

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@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
Cc: Omar Sandoval <osandov@xxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
 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


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