Re: [PATCH 04/17] block: simplify blk_mq_plug

[Damien Le Moal <damien.lemoal@opensource.wdc.com>]

On 7/4/22 21:44, Christoph Hellwig wrote:
> Drop the unused q argument, and invert the check to move the exception
> into a branch and the regular path as the normal return.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  block/blk-core.c  |  2 +-
>  block/blk-merge.c |  2 +-
>  block/blk-mq.c    |  2 +-
>  block/blk-mq.h    | 18 ++++++++----------
>  4 files changed, 11 insertions(+), 13 deletions(-)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 6bcca0b686de4..bc16e9bae2dc4 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -719,7 +719,7 @@ void submit_bio_noacct(struct bio *bio)
>  
>  	might_sleep();
>  
> -	plug = blk_mq_plug(q, bio);
> +	plug = blk_mq_plug(bio);
>  	if (plug && plug->nowait)
>  		bio->bi_opf |= REQ_NOWAIT;
>  
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 0f5f42ebd0bb0..5abf5aa5a5f0e 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -1051,7 +1051,7 @@ bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
>  	struct blk_plug *plug;
>  	struct request *rq;
>  
> -	plug = blk_mq_plug(q, bio);
> +	plug = blk_mq_plug(bio);
>  	if (!plug || rq_list_empty(plug->mq_list))
>  		return false;
>  
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 15c7c5c4ad222..dc714dff73001 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -2804,7 +2804,7 @@ static void bio_set_ioprio(struct bio *bio)
>  void blk_mq_submit_bio(struct bio *bio)
>  {
>  	struct request_queue *q = bdev_get_queue(bio->bi_bdev);
> -	struct blk_plug *plug = blk_mq_plug(q, bio);
> +	struct blk_plug *plug = blk_mq_plug(bio);
>  	const int is_sync = op_is_sync(bio->bi_opf);
>  	struct request *rq;
>  	unsigned int nr_segs = 1;
> diff --git a/block/blk-mq.h b/block/blk-mq.h
> index 31d75a83a562d..1cc0b17d69229 100644
> --- a/block/blk-mq.h
> +++ b/block/blk-mq.h
> @@ -294,7 +294,6 @@ static inline void blk_mq_clear_mq_map(struct blk_mq_queue_map *qmap)
>  
>  /*
>   * blk_mq_plug() - Get caller context plug
> - * @q: request queue
>   * @bio : the bio being submitted by the caller context
>   *
>   * Plugging, by design, may delay the insertion of BIOs into the elevator in
> @@ -305,23 +304,22 @@ static inline void blk_mq_clear_mq_map(struct blk_mq_queue_map *qmap)
>   * order. While this is not a problem with regular block devices, this ordering
>   * change can cause write BIO failures with zoned block devices as these
>   * require sequential write patterns to zones. Prevent this from happening by
> - * ignoring the plug state of a BIO issuing context if the target request queue
> - * is for a zoned block device and the BIO to plug is a write operation.
> + * ignoring the plug state of a BIO issuing context if is for a zoned block

s/if is/if it is/

> + 8 device and the BIO to plug is a write operation.

s/8/*

>   *
>   * Return current->plug if the bio can be plugged and NULL otherwise
>   */
> -static inline struct blk_plug *blk_mq_plug(struct request_queue *q,
> -					   struct bio *bio)
> +static inline struct blk_plug *blk_mq_plug( struct bio *bio)
>  {
> +	/* Zoned block device write operation case: do not plug the BIO */
> +	if (bdev_is_zoned(bio->bi_bdev) && op_is_write(bio_op(bio)))
> +		return NULL;
> +
>  	/*
>  	 * For regular block devices or read operations, use the context plug
>  	 * which may be NULL if blk_start_plug() was not executed.
>  	 */
> -	if (!bdev_is_zoned(bio->bi_bdev) || !op_is_write(bio_op(bio)))
> -		return current->plug;
> -
> -	/* Zoned block device write operation case: do not plug the BIO */
> -	return NULL;
> +	return current->plug;
>  }
>  
>  /* Free all requests on the list */

With the typos fixed, looks good.

Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>

-- 
Damien Le Moal
Western Digital Research