linux-kernel - Re: [PATCH v8 7/9] dm: Add support for copy offload.

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Message-ID: <3b9adeb6-4295-6e6a-9e93-7c5a06441830@opensource.wdc.com>
Date:   Wed, 29 Mar 2023 17:59:49 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     Anuj Gupta <anuj20.g@...sung.com>, Jens Axboe <axboe@...nel.dk>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...nel.org>, dm-devel@...hat.com,
        Keith Busch <kbusch@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        James Smart <james.smart@...adcom.com>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>
Cc:     bvanassche@....org, hare@...e.de, ming.lei@...hat.com,
        joshi.k@...sung.com, nitheshshetty@...il.com, gost.dev@...sung.com,
        Nitesh Shetty <nj.shetty@...sung.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v8 7/9] dm: Add support for copy offload.

On 3/27/23 17:40, Anuj Gupta wrote:
> From: Nitesh Shetty <nj.shetty@...sung.com>
> 

Drop the period at the end of the patch title.

> 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         | 42 +++++++++++++++++++++++++++++++++++
>  drivers/md/dm.c               |  7 ++++++
>  include/linux/device-mapper.h |  5 +++++
>  3 files changed, 54 insertions(+)
> 
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 7899f5fb4c13..45e894b9e3be 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -1863,6 +1863,39 @@ 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 < 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)
>  {
> @@ -1945,6 +1978,15 @@ int dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
>  		q->limits.discard_misaligned = 0;
>  	}
>  
> +	if (!dm_table_supports_copy(t)) {
> +		blk_queue_flag_clear(QUEUE_FLAG_COPY, q);
> +		/* Must also clear copy limits... */

Not a useful comment. The code is clear.

> +		q->limits.max_copy_sectors = 0;
> +		q->limits.max_copy_sectors_hw = 0;
> +	} else {
> +		blk_queue_flag_set(QUEUE_FLAG_COPY, q);
> +	}
> +
>  	if (!dm_table_supports_secure_erase(t))
>  		q->limits.max_secure_erase_sectors = 0;
>  
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 2d0f934ba6e6..08ec51000af8 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -1693,6 +1693,13 @@ 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 7975483816e4..44969a20295e 100644
> --- a/include/linux/device-mapper.h
> +++ b/include/linux/device-mapper.h
> @@ -380,6 +380,11 @@ 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);

-- 
Damien Le Moal
Western Digital Research