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

Nitesh Shetty
2024-05-21T13:08:12Z

[-- Attachment #1: Type: text/plain, Size: 2276 bytes --]

On 20/05/24 04:00PM, Bart Van Assche wrote:
>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.
>
Copy is a composite operation which has two operation read and
write combined, so we chose two operation types which reflects that.

>>+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.
>
We followed the naming convention from discard(bio_attempt_discard_merge)
which does similar thing.
But we are open to renaming, if overall community also feels the same.

>>@@ -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?
>
yes, blk_try_merge returns 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.
>
As described above we need two different opcodes.
As far as function renaming, we followed discard's naming. But open to
any suggestion.

>>+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.
>
Acked

Thank You
Nitesh Shetty

[-- Attachment #2: Type: text/plain, Size: 0 bytes --]