On Sat, Oct 27, 2018 at 7:50 PM Jianchao Wang
<jianchao.w.wang@xxxxxxxxxx> wrote:
>
> There are two cases when handle DISCARD merge.
> If max_discard_segments == 1, the bios/requests need to be contiguous
> to merge. If max_discard_segments > 1, it takes every bio as a range
> and different range needn't to be contiguous.
>
> But now, attempt_merge screws this up. It always consider contiguity
> for DISCARD for the case max_discard_segments > 1 and cannot merge
> contiguous DISCARD for the case max_discard_segments == 1, because
> rq_attempt_discard_merge always returns false in this case.
> This patch fixes both of the two cases above.
>
> Signed-off-by: Jianchao Wang <jianchao.w.wang@xxxxxxxxxx>
> ---
>
> V5:
> - get rid of the redundant 'else' in blk_discard_mergable
>
> V4:
> - introduce blk_try_req_merge as suggestion of Christoph.
>
> V3:
> - Introduce blk_discard_mergable into attempt_merge and
> blk_try_merge.
> - Some comment changes.
>
> V2:
> - Add max_discard_segments > 1 checking in attempt_merge.
> - Change patch title and comment.
> - Add more comment in attempt_merge
>
> block/blk-merge.c | 46 ++++++++++++++++++++++++++++++++++++----------
> 1 file changed, 36 insertions(+), 10 deletions(-)
>
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 42a4674..6b5ad27 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -714,6 +714,31 @@ static void blk_account_io_merge(struct request *req)
> part_stat_unlock();
> }
> }
> +/*
> + * Two cases of handling DISCARD merge:
> + * If max_discard_segments > 1, the driver takes every bio
> + * as a range and send them to controller together. The ranges
> + * needn't to be contiguous.
> + * Otherwise, the bios/requests will be handled as same as
> + * others which should be contiguous.
> + */
> +static inline bool blk_discard_mergable(struct request *req)
> +{
> + if (req_op(req) == REQ_OP_DISCARD &&
> + queue_max_discard_segments(req->q) > 1)
> + return true;
> + return false;
> +}
> +
> +enum elv_merge blk_try_req_merge(struct request *req, struct request *next)
> +{
> + if (blk_discard_mergable(req))
> + return ELEVATOR_DISCARD_MERGE;
> + else if (blk_rq_pos(req) + blk_rq_sectors(req) == blk_rq_pos(next))
> + return ELEVATOR_BACK_MERGE;
> +
> + return ELEVATOR_NO_MERGE;
> +}
>
> /*
> * For non-mq, this has to be called with the request spinlock acquired.
> @@ -731,12 +756,6 @@ static struct request *attempt_merge(struct request_queue *q,
> if (req_op(req) != req_op(next))
> return NULL;
>
> - /*
> - * not contiguous
> - */
> - if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
> - return NULL;
> -
> if (rq_data_dir(req) != rq_data_dir(next)
> || req->rq_disk != next->rq_disk
> || req_no_special_merge(next))
> @@ -760,11 +779,19 @@ static struct request *attempt_merge(struct request_queue *q,
> * counts here. Handle DISCARDs separately, as they
> * have separate settings.
> */
> - if (req_op(req) == REQ_OP_DISCARD) {
> +
> + switch (blk_try_req_merge(req, next)) {
> + case ELEVATOR_DISCARD_MERGE:
> if (!req_attempt_discard_merge(q, req, next))
> return NULL;
> - } else if (!ll_merge_requests_fn(q, req, next))
> + break;
> + case ELEVATOR_BACK_MERGE:
> + if (!ll_merge_requests_fn(q, req, next))
> + return NULL;
> + break;
> + default:
> return NULL;
> + }
>
> /*
> * If failfast settings disagree or any of the two is already
> @@ -888,8 +915,7 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
>
> enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
> {
> - if (req_op(rq) == REQ_OP_DISCARD &&
> - queue_max_discard_segments(rq->q) > 1)
> + if (blk_discard_mergable(rq))
> return ELEVATOR_DISCARD_MERGE;
> else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
> return ELEVATOR_BACK_MERGE;
> --
> 2.7.4
>
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
--
Ming Lei
