Re: [PATCH] block: return ELEVATOR_DISCARD_MERGE if possible

[Oleksandr Natalenko <oleksandr@natalenko.name>]

On čtvrtek 29. července 2021 5:42:26 CEST Ming Lei wrote:
> When merging one bio to request, if they are discard IO and the queue
> supports multi-range discard, we need to return ELEVATOR_DISCARD_MERGE
> because both block core and related drivers(nvme, virtio-blk) doesn't
> handle mixed discard io merge(traditional IO merge together with
> discard merge) well.
> 
> Fix the issue by returning ELEVATOR_DISCARD_MERGE in this situation,
> so both blk-mq and drivers just need to handle multi-range discard.
> 
> Reported-by: Oleksandr Natalenko <oleksandr@natalenko.name>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>  block/bfq-iosched.c      |  3 +++
>  block/blk-merge.c        | 16 ----------------
>  block/elevator.c         |  3 +++
>  block/mq-deadline-main.c |  2 ++
>  include/linux/blkdev.h   | 16 ++++++++++++++++
>  5 files changed, 24 insertions(+), 16 deletions(-)
> 
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index 727955918563..673a634eadd9 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -2361,6 +2361,9 @@ static int bfq_request_merge(struct request_queue *q,
> struct request **req, __rq = bfq_find_rq_fmerge(bfqd, bio, q);
>  	if (__rq && elv_bio_merge_ok(__rq, bio)) {
>  		*req = __rq;
> +
> +		if (blk_discard_mergable(__rq))
> +			return ELEVATOR_DISCARD_MERGE;
>  		return ELEVATOR_FRONT_MERGE;
>  	}
> 
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index a11b3b53717e..f8707ff7e2fc 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -705,22 +705,6 @@ static void blk_account_io_merge_request(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;
> -	return false;
> -}
> -
>  static enum elv_merge blk_try_req_merge(struct request *req,
>  					struct request *next)
>  {
> diff --git a/block/elevator.c b/block/elevator.c
> index 52ada14cfe45..a5fe2615ec0f 100644
> --- a/block/elevator.c
> +++ b/block/elevator.c
> @@ -336,6 +336,9 @@ enum elv_merge elv_merge(struct request_queue *q, struct
> request **req, __rq = elv_rqhash_find(q, bio->bi_iter.bi_sector);
>  	if (__rq && elv_bio_merge_ok(__rq, bio)) {
>  		*req = __rq;
> +
> +		if (blk_discard_mergable(__rq))
> +			return ELEVATOR_DISCARD_MERGE;
>  		return ELEVATOR_BACK_MERGE;
>  	}
> 
> diff --git a/block/mq-deadline-main.c b/block/mq-deadline-main.c
> index 6f612e6dc82b..294be0c0db65 100644
> --- a/block/mq-deadline-main.c
> +++ b/block/mq-deadline-main.c
> @@ -677,6 +677,8 @@ static int dd_request_merge(struct request_queue *q,
> struct request **rq,
> 
>  		if (elv_bio_merge_ok(__rq, bio)) {
>  			*rq = __rq;
> +			if (blk_discard_mergable(__rq))
> +				return ELEVATOR_DISCARD_MERGE;
>  			return ELEVATOR_FRONT_MERGE;
>  		}
>  	}
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 3177181c4326..87f00292fd7a 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1521,6 +1521,22 @@ static inline int
> queue_limit_discard_alignment(struct queue_limits *lim, sector return
> offset << SECTOR_SHIFT;
>  }
> 
> +/*
> + * 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;
> +}
> +
>  static inline int bdev_discard_alignment(struct block_device *bdev)
>  {
>  	struct request_queue *q = bdev_get_queue(bdev);

Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>

Also,

Fixes: ?

and possibly:

CC: stable@ # v5.x?

Thanks.

-- 
Oleksandr Natalenko (post-factum)