linux-kernel - Re: [PATCH v20 02/12] Add infrastructure for copy offload in block and request layer.

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Date: Mon, 20 May 2024 16:00:34 -0700
From: Bart Van Assche <bvanassche@....org>
To: Nitesh Shetty <nj.shetty@...sung.com>, Jens Axboe <axboe@...nel.dk>,
 Jonathan Corbet <corbet@....net>, Alasdair Kergon <agk@...hat.com>,
 Mike Snitzer <snitzer@...nel.org>, Mikulas Patocka <mpatocka@...hat.com>,
 Keith Busch <kbusch@...nel.org>, Christoph Hellwig <hch@....de>,
 Sagi Grimberg <sagi@...mberg.me>, Chaitanya Kulkarni <kch@...dia.com>,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>
Cc: martin.petersen@...cle.com, david@...morbit.com, hare@...e.de,
 damien.lemoal@...nsource.wdc.com, anuj20.g@...sung.com, joshi.k@...sung.com,
 nitheshshetty@...il.com, gost.dev@...sung.com, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 dm-devel@...ts.linux.dev, linux-nvme@...ts.infradead.org,
 linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v20 02/12] Add infrastructure for copy offload in block
 and request layer.

On 5/20/24 03:20, Nitesh Shetty wrote:
> Upon arrival of source bio we merge these two bio's and send
> corresponding request down to device driver.

bios with different operation types must not be merged.

> +static enum bio_merge_status bio_attempt_copy_offload_merge(struct request *req,
> +							    struct bio *bio)
> +{
> +	if (req->__data_len != bio->bi_iter.bi_size)
> +		return BIO_MERGE_FAILED;
> +
> +	req->biotail->bi_next = bio;
> +	req->biotail = bio;
> +	req->nr_phys_segments++;
> +	req->__data_len += bio->bi_iter.bi_size;
> +
> +	return BIO_MERGE_OK;
> +}

This function appends a bio to a request. Hence, the name of this function is
wrong.

> @@ -1085,6 +1124,8 @@ static enum bio_merge_status blk_attempt_bio_merge(struct request_queue *q,
>   		break;
>   	case ELEVATOR_DISCARD_MERGE:
>   		return bio_attempt_discard_merge(q, rq, bio);
> +	case ELEVATOR_COPY_OFFLOAD_MERGE:
> +		return bio_attempt_copy_offload_merge(rq, bio);
>   	default:
>   		return BIO_MERGE_NONE;
>   	}

Is any code added in this patch series that causes an I/O scheduler to return
ELEVATOR_COPY_OFFLOAD_MERGE?

> +static inline bool blk_copy_offload_mergable(struct request *req,
> +					     struct bio *bio)
> +{
> +	return (req_op(req) == REQ_OP_COPY_DST &&
> +		bio_op(bio) == REQ_OP_COPY_SRC);
> +}

bios with different operation types must not be merged. Please rename this function.

> +static inline bool op_is_copy(blk_opf_t op)
> +{
> +	return ((op & REQ_OP_MASK) == REQ_OP_COPY_SRC ||
> +		(op & REQ_OP_MASK) == REQ_OP_COPY_DST);
> +}

The above function is not used in this patch. Please introduce new functions in the
patch in which these are used for the first time.

Thanks,

Bart.