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Date:   Thu, 5 Jan 2023 09:43:13 -0500
From:   Brian Foster <bfoster@redhat.com>
To:     Sarthak Kukreti <sarthakkukreti@chromium.org>
Cc:     sarthakkukreti@google.com, dm-devel@redhat.com,
        linux-block@vger.kernel.org, linux-ext4@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        Jens Axboe <axboe@kernel.dk>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Stefan Hajnoczi <stefanha@redhat.com>,
        Alasdair Kergon <agk@redhat.com>,
        Mike Snitzer <snitzer@kernel.org>,
        Christoph Hellwig <hch@infradead.org>,
        Theodore Ts'o <tytso@mit.edu>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Bart Van Assche <bvanassche@google.com>,
        Daniil Lunev <dlunev@google.com>,
        "Darrick J. Wong" <djwong@kernel.org>
Subject: Re: [PATCH v2 2/7] dm: Add support for block provisioning
Message-ID: <Y7biAQyLKJDjsAlz@bfoster>
References: <20221229081252.452240-1-sarthakkukreti@chromium.org>
 <20221229081252.452240-3-sarthakkukreti@chromium.org>
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In-Reply-To: <20221229081252.452240-3-sarthakkukreti@chromium.org>
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On Thu, Dec 29, 2022 at 12:12:47AM -0800, Sarthak Kukreti wrote:
> Add support to dm devices for REQ_OP_PROVISION. The default mode
> is to pass through the request and dm-thin will utilize it to provision
> blocks.
> 
> Signed-off-by: Sarthak Kukreti <sarthakkukreti@chromium.org>
> ---
>  drivers/md/dm-crypt.c         |  4 +-
>  drivers/md/dm-linear.c        |  1 +
>  drivers/md/dm-snap.c          |  7 +++
>  drivers/md/dm-table.c         | 25 ++++++++++
>  drivers/md/dm-thin.c          | 90 ++++++++++++++++++++++++++++++++++-
>  drivers/md/dm.c               |  4 ++
>  include/linux/device-mapper.h | 11 +++++
>  7 files changed, 139 insertions(+), 3 deletions(-)
> 
...
> diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
> index 64cfcf46881d..ab3f1abfabaf 100644
> --- a/drivers/md/dm-thin.c
> +++ b/drivers/md/dm-thin.c
...
> @@ -1980,6 +1992,70 @@ static void process_cell(struct thin_c *tc, struct dm_bio_prison_cell *cell)
>  	}
>  }
>  
> +static void process_provision_cell(struct thin_c *tc, struct dm_bio_prison_cell *cell)
> +{
> +	int r;
> +	struct pool *pool = tc->pool;
> +	struct bio *bio = cell->holder;
> +	dm_block_t begin, end;
> +	struct dm_thin_lookup_result lookup_result;
> +
> +	if (tc->requeue_mode) {
> +		cell_requeue(pool, cell);
> +		return;
> +	}
> +
> +	get_bio_block_range(tc, bio, &begin, &end);
> +
> +	while (begin != end) {
> +		r = ensure_next_mapping(pool);
> +		if (r)
> +			/* we did our best */
> +			return;
> +
> +		r = dm_thin_find_block(tc->td, begin, 1, &lookup_result);

Hi Sarthak,

I think we discussed this before.. but remind me if/how we wanted to
handle the case if the thin blocks are shared..? Would a provision op
carry enough information to distinguish an FALLOC_FL_UNSHARE_RANGE
request from upper layers to conditionally provision in that case?

Brian

> +		switch (r) {
> +		case 0:
> +			begin++;
> +			break;
> +		case -ENODATA:
> +			bio_inc_remaining(bio);
> +			provision_block(tc, bio, begin, cell);
> +			begin++;
> +			break;
> +		default:
> +			DMERR_LIMIT(
> +				"%s: dm_thin_find_block() failed: error = %d",
> +				__func__, r);
> +			cell_defer_no_holder(tc, cell);
> +			bio_io_error(bio);
> +			begin++;
> +			break;
> +		}
> +	}
> +	bio_endio(bio);
> +	cell_defer_no_holder(tc, cell);
> +}
> +
> +static void process_provision_bio(struct thin_c *tc, struct bio *bio)
> +{
> +	dm_block_t begin, end;
> +	struct dm_cell_key virt_key;
> +	struct dm_bio_prison_cell *virt_cell;
> +
> +	get_bio_block_range(tc, bio, &begin, &end);
> +	if (begin == end) {
> +		bio_endio(bio);
> +		return;
> +	}
> +
> +	build_key(tc->td, VIRTUAL, begin, end, &virt_key);
> +	if (bio_detain(tc->pool, &virt_key, bio, &virt_cell))
> +		return;
> +
> +	process_provision_cell(tc, virt_cell);
> +}
> +
>  static void process_bio(struct thin_c *tc, struct bio *bio)
>  {
>  	struct pool *pool = tc->pool;
> @@ -2200,6 +2276,8 @@ static void process_thin_deferred_bios(struct thin_c *tc)
>  
>  		if (bio_op(bio) == REQ_OP_DISCARD)
>  			pool->process_discard(tc, bio);
> +		else if (bio_op(bio) == REQ_OP_PROVISION)
> +			process_provision_bio(tc, bio);
>  		else
>  			pool->process_bio(tc, bio);
>  
> @@ -2716,7 +2794,8 @@ static int thin_bio_map(struct dm_target *ti, struct bio *bio)
>  		return DM_MAPIO_SUBMITTED;
>  	}
>  
> -	if (op_is_flush(bio->bi_opf) || bio_op(bio) == REQ_OP_DISCARD) {
> +	if (op_is_flush(bio->bi_opf) || bio_op(bio) == REQ_OP_DISCARD ||
> +	    bio_op(bio) == REQ_OP_PROVISION) {
>  		thin_defer_bio_with_throttle(tc, bio);
>  		return DM_MAPIO_SUBMITTED;
>  	}
> @@ -3355,6 +3434,8 @@ static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv)
>  	pt->low_water_blocks = low_water_blocks;
>  	pt->adjusted_pf = pt->requested_pf = pf;
>  	ti->num_flush_bios = 1;
> +	ti->num_provision_bios = 1;
> +	ti->provision_supported = true;
>  
>  	/*
>  	 * Only need to enable discards if the pool should pass
> @@ -4053,6 +4134,7 @@ static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)
>  		blk_limits_io_opt(limits, pool->sectors_per_block << SECTOR_SHIFT);
>  	}
>  
> +
>  	/*
>  	 * pt->adjusted_pf is a staging area for the actual features to use.
>  	 * They get transferred to the live pool in bind_control_target()
> @@ -4243,6 +4325,9 @@ static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv)
>  		ti->num_discard_bios = 1;
>  	}
>  
> +	ti->num_provision_bios = 1;
> +	ti->provision_supported = true;
> +
>  	mutex_unlock(&dm_thin_pool_table.mutex);
>  
>  	spin_lock_irq(&tc->pool->lock);
> @@ -4457,6 +4542,7 @@ static void thin_io_hints(struct dm_target *ti, struct queue_limits *limits)
>  
>  	limits->discard_granularity = pool->sectors_per_block << SECTOR_SHIFT;
>  	limits->max_discard_sectors = 2048 * 1024 * 16; /* 16G */
> +	limits->max_provision_sectors = 2048 * 1024 * 16; /* 16G */
>  }
>  
>  static struct target_type thin_target = {
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index e1ea3a7bd9d9..4d19bae9da4a 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -1587,6 +1587,7 @@ static bool is_abnormal_io(struct bio *bio)
>  		case REQ_OP_DISCARD:
>  		case REQ_OP_SECURE_ERASE:
>  		case REQ_OP_WRITE_ZEROES:
> +		case REQ_OP_PROVISION:
>  			return true;
>  		default:
>  			break;
> @@ -1611,6 +1612,9 @@ static blk_status_t __process_abnormal_io(struct clone_info *ci,
>  	case REQ_OP_WRITE_ZEROES:
>  		num_bios = ti->num_write_zeroes_bios;
>  		break;
> +	case REQ_OP_PROVISION:
> +		num_bios = ti->num_provision_bios;
> +		break;
>  	default:
>  		break;
>  	}
> diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
> index 04c6acf7faaa..b4d97d5d75b8 100644
> --- a/include/linux/device-mapper.h
> +++ b/include/linux/device-mapper.h
> @@ -333,6 +333,12 @@ struct dm_target {
>  	 */
>  	unsigned num_write_zeroes_bios;
>  
> +	/*
> +	 * The number of PROVISION bios that will be submitted to the target.
> +	 * The bio number can be accessed with dm_bio_get_target_bio_nr.
> +	 */
> +	unsigned num_provision_bios;
> +
>  	/*
>  	 * The minimum number of extra bytes allocated in each io for the
>  	 * target to use.
> @@ -357,6 +363,11 @@ struct dm_target {
>  	 */
>  	bool discards_supported:1;
>  
> +	/* Set if this target needs to receive provision requests regardless of
> +	 * whether or not its underlying devices have support.
> +	 */
> +	bool provision_supported:1;
> +
>  	/*
>  	 * Set if we need to limit the number of in-flight bios when swapping.
>  	 */
> -- 
> 2.37.3
>