Re: [PATCH v3 1/2] block: adapt blk_mq_plug() to not plug for writes that require a zone lock

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

On 9/29/22 16:47, Pankaj Raghav wrote:
> The current implementation of blk_mq_plug() disables plugging for all
> operations that involves a transfer to the device as we just check if
> the last bit in op_is_write() function.
> 
> Modify blk_mq_plug() to disable plugging only for REQ_OP_WRITE and
> REQ_OP_WRITE_ZEROS as they might require a zone lock.
> 
> Suggested-by: Christoph Hellwig <hch@lst.de>
> Suggested-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>

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

> ---
>  block/blk-mq.h         | 3 ++-
>  block/blk-zoned.c      | 9 +++------
>  include/linux/blkdev.h | 9 +++++++++
>  3 files changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/block/blk-mq.h b/block/blk-mq.h
> index 8ca453ac243d..0b2870839cdd 100644
> --- a/block/blk-mq.h
> +++ b/block/blk-mq.h
> @@ -312,7 +312,8 @@ static inline void blk_mq_clear_mq_map(struct blk_mq_queue_map *qmap)
>  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)))
> +	if (IS_ENABLED(CONFIG_BLK_DEV_ZONED) &&
> +	    bdev_op_is_zoned_write(bio->bi_bdev, bio_op(bio)))
>  		return NULL;
>  
>  	/*
> diff --git a/block/blk-zoned.c b/block/blk-zoned.c
> index a264621d4905..db829401d8d0 100644
> --- a/block/blk-zoned.c
> +++ b/block/blk-zoned.c
> @@ -63,13 +63,10 @@ bool blk_req_needs_zone_write_lock(struct request *rq)
>  	if (!rq->q->disk->seq_zones_wlock)
>  		return false;
>  
> -	switch (req_op(rq)) {
> -	case REQ_OP_WRITE_ZEROES:
> -	case REQ_OP_WRITE:
> +	if (bdev_op_is_zoned_write(rq->q->disk->part0, req_op(rq)))
>  		return blk_rq_zone_is_seq(rq);
> -	default:
> -		return false;
> -	}
> +
> +	return false;
>  }
>  EXPORT_SYMBOL_GPL(blk_req_needs_zone_write_lock);
>  
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 8038c5fbde40..74bc30c680d6 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1300,6 +1300,15 @@ static inline bool bdev_is_zoned(struct block_device *bdev)
>  	return false;
>  }
>  
> +static inline bool bdev_op_is_zoned_write(struct block_device *bdev,
> +					  blk_opf_t op)
> +{
> +	if (!bdev_is_zoned(bdev))
> +		return false;
> +
> +	return op == REQ_OP_WRITE || op == REQ_OP_WRITE_ZEROES;
> +}
> +
>  static inline sector_t bdev_zone_sectors(struct block_device *bdev)
>  {
>  	struct request_queue *q = bdev_get_queue(bdev);

-- 
Damien Le Moal
Western Digital Research