On Sat, Oct 20, 2018 at 10:29:37PM +0800, Jianchao Wang wrote:
> There are two cases when handle DISCARD merge
> - max_discard_segments == 1
> bios need to be contiguous
> - max_discard_segments > 1
> Only nvme right now. 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>
> ---
>
> 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 | 24 +++++++++++++++++++-----
> 1 file changed, 19 insertions(+), 5 deletions(-)
>
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 42a4674..8f22374 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -734,8 +734,15 @@ static struct request *attempt_merge(struct request_queue *q,
> /*
> * not contiguous
> */
> - if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
> - return NULL;
> + if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next)) {
> + /*
> + * When max_discard_segments is bigger than 1 (only nvme right
> + * now), needn't consider the contiguity.
> + */
> + if (!(req_op(req) == REQ_OP_DISCARD &&
> + queue_max_discard_segments(q) > 1))
> + return NULL;
> + }
>
> if (rq_data_dir(req) != rq_data_dir(next)
> || req->rq_disk != next->rq_disk
> @@ -757,10 +764,17 @@ static struct request *attempt_merge(struct request_queue *q,
> * If we are allowed to merge, then append bio list
> * from next to rq and release next. merge_requests_fn
> * will have updated segment counts, update sector
> - * counts here. Handle DISCARDs separately, as they
> - * have separate settings.
> + * counts here.
> + * Two cases of Handling DISCARD:
> + * - max_discard_segments == 1
> + * The bios need to be contiguous.
> + * - max_discard_segments > 1
> + * Only nvme right now. It takes every bio as a
> + * range and send them to controller together. The ranges
> + * needn't to be contiguous.
> */
> - if (req_op(req) == REQ_OP_DISCARD) {
> + if (req_op(req) == REQ_OP_DISCARD &&
> + queue_max_discard_segments(q) > 1) {
> if (!req_attempt_discard_merge(q, req, next))
> return NULL;
Looks fine,
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
The above may be changed to 'if (blk_try_merge(req) == ELEVATOR_DISCARD_MERGE)'
or sort of in future, which may has document benefit at least, since
ELEVATOR_DISCARD_MERGE means multi-segment discard merge.
Thanks,
Ming
