Re: [PATCH v20 09/12] dm: Add support for copy offload

Hannes Reinecke
2024-05-21T07:11:25Z

On 5/20/24 12:20, Nitesh Shetty wrote:
> Before enabling copy for dm target, check if underlying devices and
> dm target support copy. Avoid split happening inside dm target.
> Fail early if the request needs split, currently splitting copy
> request is not supported.
>
> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
> ---
> drivers/md/dm-table.c | 37 +++++++++++++++++++++++++++++++++++
> drivers/md/dm.c | 7 +++++++
> include/linux/device-mapper.h | 3 +++
> 3 files changed, 47 insertions(+)
>
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index cc66a27c363a..d58c67ecd794 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -1899,6 +1899,38 @@ static bool dm_table_supports_nowait(struct dm_table *t)
> return true;
> }
>
> +static int device_not_copy_capable(struct dm_target *ti, struct dm_dev *dev,
> + sector_t start, sector_t len, void *data)
> +{
> + struct request_queue *q = bdev_get_queue(dev->bdev);
> +
> + return !q->limits.max_copy_sectors;
> +}
> +
> +static bool dm_table_supports_copy(struct dm_table *t)
> +{
> + struct dm_target *ti;
> + unsigned int i;
> +
> + for (i = 0; i < t->num_targets; i++) {
> + ti = dm_table_get_target(t, i);
> +
> + if (!ti->copy_offload_supported)
> + return false;
> +
> + /*
> + * target provides copy support (as implied by setting
> + * 'copy_offload_supported')
> + * and it relies on _all_ data devices having copy support.
> + */
> + if (!ti->type->iterate_devices ||
> + ti->type->iterate_devices(ti, device_not_copy_capable, NULL))
> + return false;
> + }
> +
> + return true;
> +}
> +
> static int device_not_discard_capable(struct dm_target *ti, struct dm_dev *dev,
> sector_t start, sector_t len, void *data)
> {
> @@ -1975,6 +2007,11 @@ int dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
> limits->discard_misaligned = 0;
> }
>
> + if (!dm_table_supports_copy(t)) {
> + limits->max_copy_sectors = 0;
> + limits->max_copy_hw_sectors = 0;
> + }
> +
> if (!dm_table_supports_write_zeroes(t))
> limits->max_write_zeroes_sectors = 0;
>
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 597dd7a25823..070b41b83a97 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -1717,6 +1717,13 @@ static blk_status_t __split_and_process_bio(struct clone_info *ci)
> if (unlikely(ci->is_abnormal_io))
> return __process_abnormal_io(ci, ti);
>
> + if ((unlikely(op_is_copy(ci->bio->bi_opf)) &&
> + max_io_len(ti, ci->sector) < ci->sector_count)) {
> + DMERR("Error, IO size(%u) > max target size(%llu)\n",
> + ci->sector_count, max_io_len(ti, ci->sector));
> + return BLK_STS_IOERR;
> + }
> +
> /*
> * Only support bio polling for normal IO, and the target io is
> * exactly inside the dm_io instance (verified in dm_poll_dm_io)
> diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
> index 82b2195efaca..6868941bc7d9 100644
> --- a/include/linux/device-mapper.h
> +++ b/include/linux/device-mapper.h
> @@ -397,6 +397,9 @@ struct dm_target {
> * bio_set_dev(). NOTE: ideally a target should _not_ need this.
> */
> bool needs_bio_set_dev:1;
> +
> + /* copy offload is supported */
> + bool copy_offload_supported:1;
> };
>
> void *dm_per_bio_data(struct bio *bio, size_t data_size);

Errm. Not sure this will work. DM tables might be arbitrarily, requiring
us to _split_ the copy offload request according to the underlying
component devices. But we explicitly disallowed a split in one of the
earlier patches.
Or am I wrong?

Cheers,

Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
hare@suse.de +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
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