Re: [PATCH 1/2] block: modify blk_mq_plug() to allow only reads for zoned block devices

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

On 9/26/22 03:53, Pankaj Raghav wrote:
> Modify blk_mq_plug() to allow plugging only for read operations in zoned
> block devices as there are alternative IO paths in the linux block
> layer which can end up doing a write via driver private requests in
> sequential write zones.
> 
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> ---
>   block/blk-mq.h | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/block/blk-mq.h b/block/blk-mq.h
> index 8ca453ac243d..005343df64ca 100644
> --- a/block/blk-mq.h
> +++ b/block/blk-mq.h
> @@ -305,14 +305,15 @@ static inline void blk_mq_clear_mq_map(struct blk_mq_queue_map *qmap)
>    * 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 it is for a zoned block
> - * device and the BIO to plug is a write operation.
> + * device and the BIO to plug is not a read operation.
> + *
>    *
>    * Return current->plug if the bio can be plugged and NULL otherwise
>    */
>   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)))
> +	/* Allow plugging only for read operations in zoned block devices */

nit: s/in/with

> +	if (bdev_is_zoned(bio->bi_bdev) && bio_op(bio) != REQ_OP_READ)
>   		return NULL;
>   
>   	/*

Otherwise, looks good to me.

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

-- 
Damien Le Moal
Western Digital Research