Re: [PATCH v8 2/9] block: Add copy offload support infrastructure

Damien Le Moal
2023-03-29T08:59:03Z

On 3/27/23 17:40, Anuj Gupta wrote:
> From: Nitesh Shetty <nj.shetty@samsung.com>
>
> Introduce blkdev_issue_copy which takes similar arguments as
> copy_file_range and performs copy offload between two bdevs.
> Introduce REQ_COPY copy offload operation flag. Create a read-write
> bio pair with a token as payload and submitted to the device in order.
> Read request populates token with source specific information which
> is then passed with write request.
> This design is courtesy Mikulas Patocka's token based copy
>
> Larger copy will be divided, based on max_copy_sectors limit.
>
> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
> Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
> ---
> block/blk-lib.c | 236 ++++++++++++++++++++++++++++++++++++++
> block/blk.h | 2 +
> include/linux/blk_types.h | 25 ++++
> include/linux/blkdev.h | 3 +
> 4 files changed, 266 insertions(+)
>
> diff --git a/block/blk-lib.c b/block/blk-lib.c
> index e59c3069e835..cbc6882d1e7a 100644
> --- a/block/blk-lib.c
> +++ b/block/blk-lib.c
> @@ -115,6 +115,242 @@ 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
> + * bio_copy_*_write_end_io. IO errors are propagated through cio->io_error.
> + */
> +static int cio_await_completion(struct cio *cio)

Why not simply cio_wait_completion() ?

> +{
> + int ret = 0;

No need for the initialization.

> +
> + if (cio->endio)
> + return 0;
> +
> + if (atomic_read(&cio->refcount)) {
> + __set_current_state(TASK_UNINTERRUPTIBLE);
> + blk_io_schedule();
> + }
> +
> + ret = cio->comp_len;

What about cio->io_error as the top comment mentions ? Looking at struct cio,
there is no io_error field.

> + kfree(cio);
> +
> + return ret;
> +}
> +
> +static void blk_copy_offload_write_end_io(struct bio *bio)
> +{
> + struct copy_ctx *ctx = bio->bi_private;
> + struct cio *cio = ctx->cio;
> + 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);

I do not understand. You set the length only if there was an error ? What about
the OK case ? Is this to handle partial completions ? If yes, then please add a
comment.

> + }
> + __free_page(bio->bi_io_vec[0].bv_page);
> + bio_put(bio);
> +
> + kfree(ctx);
> + if (atomic_dec_and_test(&cio->refcount)) {

Reverse this condition and return early.

> + if (cio->endio) {
> + cio->endio(cio->private, cio->comp_len);
> + kfree(cio);
> + } else
> + blk_wake_io_task(cio->waiter);

Missing curly braces for the else.

> + }
> +}
> +
> +static void blk_copy_offload_read_end_io(struct bio *read_bio)
> +{
> + struct copy_ctx *ctx = read_bio->bi_private;
> + struct cio *cio = ctx->cio;
> + sector_t clen;
> +
> + if (read_bio->bi_status) {
> + clen = (read_bio->bi_iter.bi_sector << SECTOR_SHIFT)
> + - cio->pos_in;
> + cio->comp_len = min_t(sector_t, clen, cio->comp_len);
> + __free_page(read_bio->bi_io_vec[0].bv_page);
> + bio_put(ctx->write_bio);
> + bio_put(read_bio);
> + kfree(ctx);
> + if (atomic_dec_and_test(&cio->refcount)) {
> + if (cio->endio) {
> + cio->endio(cio->private, cio->comp_len);
> + kfree(cio);
> + } else
> + blk_wake_io_task(cio->waiter);

Missing curly braces for the else.

> + }
> + return;

So you do all this only if there was an error ? What about an OK bio completion
(bi_status == BLK_STS_OK) ?

> + }
> +
> + schedule_work(&ctx->dispatch_work);
> + bio_put(read_bio);
> +}
> +
> +static void blk_copy_dispatch_work_fn(struct work_struct *work)
> +{
> + struct copy_ctx *ctx = container_of(work, struct copy_ctx,
> + dispatch_work);
> +
> + submit_bio(ctx->write_bio);
> +}
> +
> +/*
> + * __blk_copy_offload - Use device's native copy offload feature.
> + * we perform copy operation by sending 2 bio.
> + * 1. First we send a read bio with REQ_COPY flag along with a token and source
> + * and length. Once read bio reaches driver layer, device driver adds all the
> + * source info to token and does a fake completion.
> + * 2. Once read operation completes, we issue write with REQ_COPY flag with same
> + * token. In driver layer, token info is used to form a copy offload command.
> + *
> + * returns the length of bytes copied or negative error value
> + */
> +static int __blk_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)
> +{
> + struct cio *cio;
> + struct copy_ctx *ctx;
> + struct bio *read_bio, *write_bio;
> + struct page *token;
> + sector_t copy_len;
> + sector_t rem, max_copy_len;
> +
> + cio = kzalloc(sizeof(struct cio), GFP_KERNEL);
> + if (!cio)
> + return -ENOMEM;
> + atomic_set(&cio->refcount, 0);
> + cio->waiter = current;
> + cio->endio = end_io;
> + cio->private = private;
> +
> + max_copy_len = min(bdev_max_copy_sectors(bdev_in),
> + bdev_max_copy_sectors(bdev_out)) << SECTOR_SHIFT;
> +
> + cio->pos_in = pos_in;
> + cio->pos_out = pos_out;
> + cio->comp_len = len;
> + for (rem = len; rem > 0; rem -= copy_len) {
> + copy_len = min(rem, max_copy_len);
> +
> + token = alloc_page(gfp_mask);
> + if (unlikely(!token))
> + goto err_token;
> +
> + ctx = kzalloc(sizeof(struct copy_ctx), gfp_mask);
> + if (!ctx)
> + goto err_ctx;
> + read_bio = bio_alloc(bdev_in, 1, REQ_OP_READ | REQ_COPY
> + | REQ_SYNC | REQ_NOMERGE, gfp_mask);
> + if (!read_bio)
> + goto err_read_bio;
> + write_bio = bio_alloc(bdev_out, 1, REQ_OP_WRITE
> + | REQ_COPY | REQ_SYNC | REQ_NOMERGE, gfp_mask);
> + if (!write_bio)
> + goto err_write_bio;
> +
> + ctx->cio = cio;
> + ctx->write_bio = write_bio;
> + INIT_WORK(&ctx->dispatch_work, blk_copy_dispatch_work_fn);
> +
> + __bio_add_page(read_bio, token, PAGE_SIZE, 0);
> + read_bio->bi_iter.bi_size = copy_len;
> + read_bio->bi_iter.bi_sector = pos_in >> SECTOR_SHIFT;
> + read_bio->bi_end_io = blk_copy_offload_read_end_io;
> + read_bio->bi_private = ctx;
> +
> + __bio_add_page(write_bio, token, PAGE_SIZE, 0);
> + write_bio->bi_iter.bi_size = copy_len;
> + write_bio->bi_end_io = blk_copy_offload_write_end_io;
> + write_bio->bi_iter.bi_sector = pos_out >> SECTOR_SHIFT;
> + write_bio->bi_private = ctx;
> +
> + atomic_inc(&cio->refcount);
> + submit_bio(read_bio);
> + pos_in += copy_len;
> + pos_out += copy_len;
> + }
> +
> + /* Wait for completion of all IO's*/
> + return cio_await_completion(cio);
> +
> +err_write_bio:
> + bio_put(read_bio);
> +err_read_bio:
> + kfree(ctx);
> +err_ctx:
> + __free_page(token);
> +err_token:
> + cio->comp_len = min_t(sector_t, cio->comp_len, (len - rem));

Why ? cio_wait_completion() return that, no ?

> + return cio_await_completion(cio);
> +}
> +
> +static inline int blk_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 >= MAX_COPY_TOTAL_LENGTH)
> + return -EINVAL;
> +
> + return 0;
> +}
> +
> +static inline bool blk_check_copy_offload(struct request_queue *q_in,
> + struct request_queue *q_out)
> +{
> + return blk_queue_copy(q_in) && blk_queue_copy(q_out);
> +}

Not a very useful helper.

> +
> +/*
> + * @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
> + * @end_io: end_io function to be called on completion of copy operation,
> + * for synchronous operation this should be NULL
> + * @private: end_io 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 a negative error value
> + *
> + * Description:
> + * Copy source offset from source block device to destination block
> + * device. length of a source range cannot be zero. Max total length of
> + * copy is limited to MAX_COPY_TOTAL_LENGTH
> + */
> +int blkdev_issue_copy(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)
> +{
> + struct request_queue *q_in = bdev_get_queue(bdev_in);
> + struct request_queue *q_out = bdev_get_queue(bdev_out);
> + int ret = -EINVAL;
> +
> + ret = blk_copy_sanity_check(bdev_in, pos_in, bdev_out, pos_out, len);
> + if (ret)
> + return ret;
> +
> + if (blk_check_copy_offload(q_in, q_out))
> + ret = __blk_copy_offload(bdev_in, pos_in, bdev_out, pos_out,
> + len, end_io, private, gfp_mask);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(blkdev_issue_copy);
> +
> 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.h b/block/blk.h
> index d65d96994a94..684b8fa121db 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -311,6 +311,8 @@ 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/include/linux/blk_types.h b/include/linux/blk_types.h
> index a0e339ff3d09..7f586c4b9954 100644
> --- a/include/linux/blk_types.h
> +++ b/include/linux/blk_types.h
> @@ -423,6 +423,7 @@ enum req_flag_bits {
> */
> /* for REQ_OP_WRITE_ZEROES: */
> __REQ_NOUNMAP, /* do not free blocks when zeroing */
> + __REQ_COPY, /* copy request */
>
> __REQ_NR_BITS, /* stops here */
> };
> @@ -452,6 +453,7 @@ enum req_flag_bits {
>
> #define REQ_DRV (__force blk_opf_t)(1ULL << __REQ_DRV)
> #define REQ_SWAP (__force blk_opf_t)(1ULL << __REQ_SWAP)
> +#define REQ_COPY ((__force blk_opf_t)(1ULL << __REQ_COPY))
>
> #define REQ_FAILFAST_MASK \
> (REQ_FAILFAST_DEV | REQ_FAILFAST_TRANSPORT | REQ_FAILFAST_DRIVER)
> @@ -478,6 +480,11 @@ 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_COPY);

No need for the parenthesis.

> +}
> +
> /*
> * Check if the bio or request is one that needs special treatment in the
> * flush state machine.
> @@ -537,4 +544,22 @@ struct blk_rq_stat {
> u64 batch;
> };
>
> +typedef void (cio_iodone_t)(void *private, int comp_len);

Not really needed I think.

> +
> +struct cio {
> + struct task_struct *waiter; /* waiting task (NULL if none) */
> + atomic_t refcount;
> + loff_t pos_in;
> + loff_t pos_out;
> + size_t comp_len;
> + cio_iodone_t *endio; /* applicable for async operation */
> + void *private; /* applicable for async operation */
> +};
> +
> +struct copy_ctx {
> + struct cio *cio;
> + struct work_struct dispatch_work;
> + struct bio *write_bio;
> +};
> +
> #endif /* __LINUX_BLK_TYPES_H */
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 200338f2ec2e..1bb43697d43d 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1054,6 +1054,9 @@ 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);
> +int blkdev_issue_copy(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