linux-kernel - Re: [PATCH v3 08/10] dm: Add support for copy offload.

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Date:   Tue, 22 Feb 2022 11:00:31 -0500
From:   Mike Snitzer <snitzer@...hat.com>
To:     Nitesh Shetty <nj.shetty@...sung.com>
Cc:     javier@...igon.com, chaitanyak@...dia.com,
        linux-block@...r.kernel.org, linux-scsi@...r.kernel.org,
        dm-devel@...hat.com, linux-nvme@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, axboe@...nel.dk,
        msnitzer@...hat.com, bvanassche@....org,
        martin.petersen@...cle.com, hare@...e.de, kbusch@...nel.org,
        hch@....de, Frederick.Knight@...app.com, osandov@...com,
        lsf-pc@...ts.linux-foundation.org, djwong@...nel.org,
        josef@...icpanda.com, clm@...com, dsterba@...e.com, tytso@....edu,
        jack@...e.com, joshi.k@...sung.com, arnav.dawn@...sung.com,
        nitheshshetty@...il.com, Alasdair Kergon <agk@...hat.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        James Smart <james.smart@...adcom.com>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 08/10] dm: Add support for copy offload.

On Mon, Feb 14 2022 at  2:59P -0500,
Nitesh Shetty <nj.shetty@...sung.com> 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@...sung.com>
> ---
>  drivers/md/dm-table.c         | 45 +++++++++++++++++++++++++++++++++++
>  drivers/md/dm.c               |  6 +++++
>  include/linux/device-mapper.h |  5 ++++
>  3 files changed, 56 insertions(+)
> 
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index e43096cfe9e2..8dc9ae6a6a86 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -1903,6 +1903,38 @@ 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 !blk_queue_copy(q);
> +}
> +
> +static bool dm_table_supports_copy(struct dm_table *t)
> +{
> +	struct dm_target *ti;
> +	unsigned int i;
> +
> +	for (i = 0; i < dm_table_get_num_targets(t); i++) {
> +		ti = dm_table_get_target(t, i);
> +
> +		if (!ti->copy_supported)
> +			return false;
> +
> +		/*
> +		 * target provides copy support (as implied by setting
> +		 * 'copy_supported') and it relies on _all_ data devices having copy support.
> +		 */
> +		if (ti->copy_supported &&
> +		    (!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)
>  {
> @@ -2000,6 +2032,19 @@ int dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
>  	} else
>  		blk_queue_flag_set(QUEUE_FLAG_DISCARD, q);
>  
> +	if (!dm_table_supports_copy(t)) {
> +		blk_queue_flag_clear(QUEUE_FLAG_COPY, q);
> +		/* Must also clear discard limits... */

copy-and-paste mistake: s/discard/copy/ ^

> +		q->limits.max_copy_sectors = 0;
> +		q->limits.max_hw_copy_sectors = 0;
> +		q->limits.max_copy_range_sectors = 0;
> +		q->limits.max_hw_copy_range_sectors = 0;
> +		q->limits.max_copy_nr_ranges = 0;
> +		q->limits.max_hw_copy_nr_ranges = 0;
> +	} else {
> +		blk_queue_flag_set(QUEUE_FLAG_COPY, q);
> +	}
> +
>  	if (dm_table_supports_secure_erase(t))
>  		blk_queue_flag_set(QUEUE_FLAG_SECERASE, q);
>  
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index ab9cc91931f9..3b4cd49c489d 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -1372,6 +1372,12 @@ static int __split_and_process_non_flush(struct clone_info *ci)
>  	if (__process_abnormal_io(ci, ti, &r))
>  		return r;
>  
> +	if ((unlikely(op_is_copy(ci->bio->bi_opf)) &&
> +				max_io_len(ti, ci->sector) < ci->sector_count)) {
> +		DMERR("%s: Error IO size(%u) is greater than maximum target size(%llu)\n",
> +				__func__, ci->sector_count, max_io_len(ti, ci->sector));
> +		return -EIO;
> +	}
>  	len = min_t(sector_t, max_io_len(ti, ci->sector), ci->sector_count);
>  
>  	r = __clone_and_map_data_bio(ci, ti, ci->sector, &len);

There isn't a need for __func__ prefix here.

You'll also need to rebase on latest dm-5.18 (or wait until 5.18 merge
window opens) because there has been some conflicting changes since
you posted.

> diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
> index b26fecf6c8e8..acfd4018125a 100644
> --- a/include/linux/device-mapper.h
> +++ b/include/linux/device-mapper.h
> @@ -362,6 +362,11 @@ struct dm_target {
>  	 * zone append operations using regular writes.
>  	 */
>  	bool emulate_zone_append:1;
> +
> +	/*
> +	 * copy offload is supported
> +	 */
> +	bool copy_supported:1;
>  };

Would prefer this be "copy_offload_supported".

>  
>  void *dm_per_bio_data(struct bio *bio, size_t data_size);
> -- 
> 2.30.0-rc0
>