Re: [PATCH V4] block: fix the DISCARD request merge
From: Jens Axboe
Date: Fri Oct 26 2018 - 10:26:03 EST
On 10/26/18 3:28 AM, Jianchao Wang 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.
Looks good to me, but:
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 42a4674..cf817c7a 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -714,6 +714,32 @@ static void blk_account_io_merge(struct request *req)
> + * 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;
> + else
> + return false;
Please get rid of the redundant else.