Re: [PATCH v2 6/7] block: implement async wire write zeroes

[Christoph Hellwig <hch@infradead.org>]

On Thu, Aug 22, 2024 at 04:35:56AM +0100, Pavel Begunkov wrote:
> Add another io_uring cmd for block layer implementing asynchronous write
> zeroes. It reuses helpers we've added for async discards, and inherits
> the code structure as well as all considerations in regards to page
> cache races.

Most comments from discard apply here as well.

> +static int blkdev_queue_cmd(struct io_uring_cmd *cmd, struct block_device *bdev,
> +			    uint64_t start, uint64_t len, sector_t limit,
> +			    blk_opf_t opf)

This feels a little over generic as it doesn't just queue any random
command.

> +static int blkdev_cmd_write_zeroes(struct io_uring_cmd *cmd,
> +				   struct block_device *bdev,
> +				   uint64_t start, uint64_t len, bool nowait)
> +{
> +	blk_opf_t opf = REQ_OP_WRITE_ZEROES | REQ_NOUNMAP;
> +
> +	if (nowait)
> +		opf |= REQ_NOWAIT;
> +	return blkdev_queue_cmd(cmd, bdev, start, len,
> +				bdev_write_zeroes_sectors(bdev), opf);

So no support for fallback to Write of zero page here?  That's probably
the case where the async offload is needed most.

> +struct bio *blk_alloc_write_zeroes_bio(struct block_device *bdev,
> +					sector_t *sector, sector_t *nr_sects,
> +					gfp_t gfp_mask);

Please keep this in block/blk.h, no need to expose it to the entire
kernel.