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

Damien Le Moal
2023-06-28T08:11:03Z

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 ?

> 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.

> +}
> +
> +/*
> + * __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.

> +
> + cio->pos_in = pos_in;
> + cio->pos_out = pos_out;
> + /* If there is a error, comp_len will be set to least successfully
> + * completed copied length
> + */
> + cio->comp_len = len;
> + for (rem = len; rem > 0; rem -= copy_len) {
> + copy_len = min(rem, max_copy_len);
> +
> + write_bio = bio_alloc(bdev_out, 0, REQ_OP_COPY_DST, gfp_mask);
> + if (!write_bio)
> + goto err_write_bio_alloc;
> + write_bio->bi_iter.bi_size = copy_len;
> + write_bio->bi_iter.bi_sector = pos_out >> SECTOR_SHIFT;
> +
> + blk_start_plug(&plug);
> + read_bio = blk_next_bio(write_bio, bdev_in, 0, REQ_OP_COPY_SRC,
> + gfp_mask);
> + read_bio->bi_iter.bi_size = copy_len;
> + read_bio->bi_iter.bi_sector = pos_in >> SECTOR_SHIFT;
> + read_bio->bi_end_io = blkdev_copy_offload_read_endio;
> + read_bio->bi_private = cio;
> +
> + atomic_inc(&cio->refcount);
> + submit_bio(read_bio);
> + blk_finish_plug(&plug);
> + pos_in += copy_len;
> + pos_out += copy_len;
> + }
> +
> + return blkdev_copy_wait_io_completion(cio);
> +
> +err_write_bio_alloc:
> + cio->comp_len = min_t(sector_t, cio->comp_len, (len - rem));
> + if (!atomic_read(&cio->refcount)) {
> + kfree(cio);
> + return -ENOMEM;
> + }
> + return blkdev_copy_wait_io_completion(cio);
> +}
> +
> +static inline ssize_t blkdev_copy_sanity_check(
> + struct block_device *bdev_in, loff_t pos_in,
> + struct block_device *bdev_out, loff_t pos_out,
> + size_t len)
> +{
> + unsigned int align = max(bdev_logical_block_size(bdev_out),
> + bdev_logical_block_size(bdev_in)) - 1;
> +
> + if (bdev_read_only(bdev_out))
> + return -EPERM;
> +
> + if ((pos_in & align) || (pos_out & align) || (len & align) || !len ||
> + len >= COPY_MAX_BYTES)
> + return -EINVAL;
> +
> + return 0;
> +}
> +
> +/*
> + * @bdev_in: source block device
> + * @pos_in: source offset
> + * @bdev_out: destination block device
> + * @pos_out: destination offset
> + * @len: length in bytes to be copied
> + * @endio: endio function to be called on completion of copy operation,
> + * for synchronous operation this should be NULL
> + * @private: endio function will be called with this private data, should be
> + * NULL, if operation is synchronous in nature
> + * @gfp_mask: memory allocation flags (for bio_alloc)
> + *
> + * Returns the length of bytes copied or error if encountered
> + *
> + * Description:
> + * Copy source offset from source block device to destination block
> + * device. If copy offload is not supported or fails, fallback to
> + * emulation. Max total length of copy is limited to COPY_MAX_BYTES
> + */
> +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 request_queue *q_in = bdev_get_queue(bdev_in);
> + struct request_queue *q_out = bdev_get_queue(bdev_out);
> + ssize_t ret;
> +
> + ret = blkdev_copy_sanity_check(bdev_in, pos_in, bdev_out, pos_out, len);
> + if (ret)
> + return ret;
> +
> + if (blk_queue_copy(q_in) && blk_queue_copy(q_out))
> + ret = __blkdev_copy_offload(bdev_in, pos_in, bdev_out, pos_out,
> + len, endio, private, gfp_mask);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(blkdev_copy_offload);
> +
> static int __blkdev_issue_write_zeroes(struct block_device *bdev,
> sector_t sector, sector_t nr_sects, gfp_t gfp_mask,
> struct bio **biop, unsigned flags)
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 65e75efa9bd3..bfd86c54df22 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -922,6 +922,9 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
> if (!rq_mergeable(rq) || !bio_mergeable(bio))
> return false;
>
> + if ((req_op(rq) == REQ_OP_COPY_DST) && (bio_op(bio) == REQ_OP_COPY_SRC))
> + return true;
> +
> if (req_op(rq) != bio_op(bio))
> return false;
>
> @@ -951,6 +954,8 @@ enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
> {
> if (blk_discard_mergable(rq))
> return ELEVATOR_DISCARD_MERGE;
> + else if (blk_copy_offload_mergable(rq, bio))
> + return ELEVATOR_COPY_OFFLOAD_MERGE;
> else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
> return ELEVATOR_BACK_MERGE;
> else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
> @@ -1053,6 +1058,20 @@ static enum bio_merge_status bio_attempt_discard_merge(struct request_queue *q,
> return BIO_MERGE_FAILED;
> }
>
> +static enum bio_merge_status bio_attempt_copy_offload_merge(
> + struct request_queue *q, 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 = blk_rq_nr_phys_segments(req) + 1;
> + req->__data_len += bio->bi_iter.bi_size;
> +
> + return BIO_MERGE_OK;
> +}
> +
> static enum bio_merge_status blk_attempt_bio_merge(struct request_queue *q,
> struct request *rq,
> struct bio *bio,
> @@ -1073,6 +1092,8 @@ 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(q, rq, bio);
> default:
> return BIO_MERGE_NONE;
> }
> diff --git a/block/blk.h b/block/blk.h
> index 608c5dcc516b..440bfa148461 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -156,6 +156,13 @@ static inline bool blk_discard_mergable(struct request *req)
> return false;
> }
>
> +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));
> +}
> +
> static inline unsigned int blk_rq_get_max_segments(struct request *rq)
> {
> if (req_op(rq) == REQ_OP_DISCARD)
> @@ -303,6 +310,8 @@ static inline bool bio_may_exceed_limits(struct bio *bio,
> break;
> }
>
> + if (unlikely(op_is_copy(bio->bi_opf)))
> + return false;
> /*
> * All drivers must accept single-segments bios that are <= PAGE_SIZE.
> * This is a quick and dirty check that relies on the fact that
> diff --git a/block/elevator.h b/block/elevator.h
> index 7ca3d7b6ed82..eec442bbf384 100644
> --- a/block/elevator.h
> +++ b/block/elevator.h
> @@ -18,6 +18,7 @@ enum elv_merge {
> ELEVATOR_FRONT_MERGE = 1,
> ELEVATOR_BACK_MERGE = 2,
> ELEVATOR_DISCARD_MERGE = 3,
> + ELEVATOR_COPY_OFFLOAD_MERGE = 4,
> };
>
> struct blk_mq_alloc_data;
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index c4f5b5228105..a2673f24e493 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -57,7 +57,9 @@ static inline bool bio_has_data(struct bio *bio)
> bio->bi_iter.bi_size &&
> bio_op(bio) != REQ_OP_DISCARD &&
> bio_op(bio) != REQ_OP_SECURE_ERASE &&
> - bio_op(bio) != REQ_OP_WRITE_ZEROES)
> + bio_op(bio) != REQ_OP_WRITE_ZEROES &&
> + bio_op(bio) != REQ_OP_COPY_DST &&
> + bio_op(bio) != REQ_OP_COPY_SRC)
> return true;
>
> return false;
> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> index 0bad62cca3d0..336146798e56 100644
> --- a/include/linux/blk_types.h
> +++ b/include/linux/blk_types.h
> @@ -394,6 +394,9 @@ enum req_op {
> /* reset all the zone present on the device */
> REQ_OP_ZONE_RESET_ALL = (__force blk_opf_t)17,
>
> + REQ_OP_COPY_SRC = (__force blk_opf_t)18,
> + REQ_OP_COPY_DST = (__force blk_opf_t)19,
> +
> /* Driver private requests */
> REQ_OP_DRV_IN = (__force blk_opf_t)34,
> REQ_OP_DRV_OUT = (__force blk_opf_t)35,
> @@ -482,6 +485,12 @@ static inline bool op_is_write(blk_opf_t op)
> return !!(op & (__force blk_opf_t)1);
> }
>
> +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));
> +}
> +
> /*
> * Check if the bio or request is one that needs special treatment in the
> * flush state machine.
> @@ -541,4 +550,16 @@ struct blk_rq_stat {
> u64 batch;
> };
>
> +typedef void (cio_iodone_t)(void *private, int comp_len);
> +
> +struct cio {
> + struct task_struct *waiter; /* waiting task (NULL if none) */
> + loff_t pos_in;
> + loff_t pos_out;
> + ssize_t comp_len;
> + cio_iodone_t *endio; /* applicable for async operation */
> + void *private; /* applicable for async operation */
> + atomic_t refcount;
> +};
> +
> #endif /* __LINUX_BLK_TYPES_H */
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 6098665953e6..963f5c97dec0 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1043,6 +1043,10 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
> sector_t nr_sects, gfp_t gfp_mask, struct bio **biop);
> int blkdev_issue_secure_erase(struct block_device *bdev, sector_t sector,
> sector_t nr_sects, gfp_t gfp);
> +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 end_io, void *private, gfp_t gfp_mask);
>
> #define BLKDEV_ZERO_NOUNMAP (1 << 0) /* do not free blocks */
> #define BLKDEV_ZERO_NOFALLBACK (1 << 1) /* don't write explicit zeroes */

--
Damien Le Moal
Western Digital Research