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Subject[PATCH] block: respect virtual boundary mask in bvecs
With drivers like iSer we are seeing a lot of bio splitting and smaller I/Os
being submitted to the driver.

The root cause of this issue that the virtual boundary mask code does not take
into consideration that some of the memory segments in the SG list may have
come from a huge memory page that is being managed in the SG list as 4K
blocks. This means that many of the segments in the SG list will have an
offset into the page that is not 0 but will be a multiple of 4K.

Cc: Jan Kara <>
Cc: Sagi Grimberg <>
Signed-off-by: Johannes Thumshirn <>
block/blk-merge.c | 2 +-
block/blk.h | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 6b5ad275ed56..208658a901c6 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -46,7 +46,7 @@ static inline bool bio_will_gap(struct request_queue *q,
bio_get_first_bvec(prev_rq->bio, &pb);
bio_get_first_bvec(prev, &pb);
- if (pb.bv_offset)
+ if (pb.bv_offset & queue_virt_boundary(q))
return true;

diff --git a/block/blk.h b/block/blk.h
index a1841b8ff129..c85e53f21cdd 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -169,7 +169,7 @@ static inline bool biovec_phys_mergeable(struct request_queue *q,
static inline bool __bvec_gap_to_prev(struct request_queue *q,
struct bio_vec *bprv, unsigned int offset)
- return offset ||
+ return (offset & queue_virt_boundary(q)) ||
((bprv->bv_offset + bprv->bv_len) & queue_virt_boundary(q));

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