On Mon, Nov 05, 2018 at 11:23:01AM +0100, Johannes Thumshirn wrote:
> 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.
I probably got this wrong, but I thought a 2M huge page was 512 regular
pages with a compound head, and offsets were from those regular pages
rather than from the head.
Overall though, the patch makes sense to me for this and other reasons.
Acked-by: Keith Busch <keith.busch@xxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Sagi Grimberg <sagi@xxxxxxxxxxx>
> Signed-off-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
> ---
> 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);
> else
> 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));
> }
>
> --
