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

[Pavel Begunkov <asml.silence@gmail.com>]

On 8/22/24 07:50, Christoph Hellwig wrote:
> 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.

Fair enough, but I believe it's more reasonable to have a separate
cmd for it instead of silently falling back.

-- 
Pavel Begunkov