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

Bart Van Assche
2024-05-20T23:00:54Z

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.