Re: [PATCH v13 2/9] block: Add copy offload support infrastructure

Nitesh Shetty
2023-06-29T07:48:13Z

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On 23/06/28 03:45PM, Damien Le Moal wrote:
>On 6/28/23 03:36, Nitesh Shetty wrote:
>> Introduce blkdev_copy_offload which takes similar arguments as
>> copy_file_range and performs copy offload between two bdevs.
>
>I am confused... I thought it was discussed to only allow copy offload only
>within a single bdev for now... Did I missi something ?
>

Yes, you are right. copy is supported within single bdev only.
We will update this.

>> Introduce REQ_OP_COPY_DST, REQ_OP_COPY_SRC operation.
>> Issue REQ_OP_COPY_DST with destination info along with taking a plug.
>> This flows till request layer and waits for src bio to get merged.
>> Issue REQ_OP_COPY_SRC with source info and this bio reaches request
>> layer and merges with dst request.
>> For any reason, if request comes to driver with either only one of src/dst
>> info we fail the copy offload.
>>
>> Larger copy will be divided, based on max_copy_sectors limit.
>>
>> Suggested-by: Christoph Hellwig <hch@lst.de>
>> Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
>> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
>> ---
>> block/blk-core.c | 5 ++
>> block/blk-lib.c | 177 ++++++++++++++++++++++++++++++++++++++
>> block/blk-merge.c | 21 +++++
>> block/blk.h | 9 ++
>> block/elevator.h | 1 +
>> include/linux/bio.h | 4 +-
>> include/linux/blk_types.h | 21 +++++
>> include/linux/blkdev.h | 4 +
>> 8 files changed, 241 insertions(+), 1 deletion(-)
>>
>> diff --git a/block/blk-core.c b/block/blk-core.c
>> index 99d8b9812b18..e6714391c93f 100644
>> --- a/block/blk-core.c
>> +++ b/block/blk-core.c
>> @@ -796,6 +796,11 @@ void submit_bio_noacct(struct bio *bio)
>> if (!q->limits.max_write_zeroes_sectors)
>> goto not_supported;
>> break;
>> + case REQ_OP_COPY_SRC:
>> + case REQ_OP_COPY_DST:
>> + if (!blk_queue_copy(q))
>> + goto not_supported;
>> + break;
>> default:
>> break;
>> }
>> diff --git a/block/blk-lib.c b/block/blk-lib.c
>> index e59c3069e835..10c3eadd5bf6 100644
>> --- a/block/blk-lib.c
>> +++ b/block/blk-lib.c
>> @@ -115,6 +115,183 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
>> }
>> EXPORT_SYMBOL(blkdev_issue_discard);
>>
>> +/*
>> + * For synchronous copy offload/emulation, wait and process all in-flight BIOs.
>> + * This must only be called once all bios have been issued so that the refcount
>> + * can only decrease. This just waits for all bios to make it through
>> + * blkdev_copy_(offload/emulate)_(read/write)_endio.
>> + */
>> +static ssize_t blkdev_copy_wait_io_completion(struct cio *cio)
>> +{
>> + ssize_t ret;
>> +
>> + if (cio->endio)
>> + return 0;
>> +
>> + if (atomic_read(&cio->refcount)) {
>> + __set_current_state(TASK_UNINTERRUPTIBLE);
>> + blk_io_schedule();
>> + }
>> +
>> + ret = cio->comp_len;
>> + kfree(cio);
>> +
>> + return ret;
>> +}
>> +
>> +static void blkdev_copy_offload_read_endio(struct bio *bio)
>> +{
>> + struct cio *cio = bio->bi_private;
>> + sector_t clen;
>> +
>> + if (bio->bi_status) {
>> + clen = (bio->bi_iter.bi_sector << SECTOR_SHIFT) - cio->pos_out;
>> + cio->comp_len = min_t(sector_t, clen, cio->comp_len);
>> + }
>> + bio_put(bio);
>> +
>> + if (!atomic_dec_and_test(&cio->refcount))
>> + return;
>> + if (cio->endio) {
>> + cio->endio(cio->private, cio->comp_len);
>> + kfree(cio);
>> + } else
>> + blk_wake_io_task(cio->waiter);
>
>Curly brackets around else missing.
>

Acked.

>> +}
>> +
>> +/*
>> + * __blkdev_copy_offload - Use device's native copy offload feature.
>> + * we perform copy operation by sending 2 bio.
>> + * 1. We take a plug and send a REQ_OP_COPY_DST bio along with destination
>> + * sector and length. Once this bio reaches request layer, we form a request and
>> + * wait for src bio to arrive.
>> + * 2. We issue REQ_OP_COPY_SRC bio along with source sector and length. Once
>> + * this bio reaches request layer and find a request with previously sent
>> + * destination info we merge the source bio and return.
>> + * 3. Release the plug and request is sent to driver
>> + *
>> + * Returns the length of bytes copied or error if encountered
>> + */
>> +static ssize_t __blkdev_copy_offload(
>> + struct block_device *bdev_in, loff_t pos_in,
>> + struct block_device *bdev_out, loff_t pos_out,
>> + size_t len, cio_iodone_t endio, void *private, gfp_t gfp_mask)
>> +{
>> + struct cio *cio;
>> + struct bio *read_bio, *write_bio;
>> + sector_t rem, copy_len, max_copy_len;
>> + struct blk_plug plug;
>> +
>> + cio = kzalloc(sizeof(struct cio), GFP_KERNEL);
>> + if (!cio)
>> + return -ENOMEM;
>> + atomic_set(&cio->refcount, 0);
>> + cio->waiter = current;
>> + cio->endio = endio;
>> + cio->private = private;
>> +
>> + max_copy_len = min(bdev_max_copy_sectors(bdev_in),
>> + bdev_max_copy_sectors(bdev_out)) << SECTOR_SHIFT;
>
>According to patch 1, this can end up being 0, so the loop below will be infinite.
>

Agreed. As you suggested earlier, once we remove copy_offload parameter
and checking copy_max_sector to identify copy offload capabilty should
solve this.

Thank you,
Nitesh Shetty

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