Re: [PATCH v7 13/13] dm: add non power of 2 zoned target

From: Damien Le Moal <damien.lemoal@opensource.wdc.com>
To: Pankaj Raghav <p.raghav@samsung.com>,
	hch@lst.de, snitzer@redhat.com, axboe@kernel.dk
Cc: bvanassche@acm.org, linux-kernel@vger.kernel.org,
	jiangbo.365@bytedance.com, hare@suse.de, pankydev8@gmail.com,
	dm-devel@redhat.com, jonathan.derrick@linux.dev,
	gost.dev@samsung.com, dsterba@suse.com, jaegeuk@kernel.org,
	linux-nvme@lists.infradead.org, Johannes.Thumshirn@wdc.com,
	linux-block@vger.kernel.org,
	Damien Le Moal <damien.lemoal@wdc.com>
Subject: Re: [PATCH v7 13/13] dm: add non power of 2 zoned target
Date: Fri, 17 Jun 2022 15:12:01 +0900	[thread overview]
Message-ID: <e0dc08fd-cd00-240d-edc4-5799d51aa5a8@opensource.wdc.com> (raw)
In-Reply-To: <4746a000-2220-211e-1bd6-79c15c18a85c@samsung.com>

On 6/17/22 14:45, Pankaj Raghav wrote:
> On 2022-06-17 01:49, Damien Le Moal wrote:
>>>> Why do you need to change dm_set_zones_restrictions() at all ?
>>>>
>>> When the device mapper is created, the q->limits gets inherited from the
>>> underlying device. The chunk sectors of the target and the device will
>>> be the same but we want the chunk sector of the target to be different
>>> (rounded to po2) compared to the underlying device's chunk sector. This
>>> needs to be done only for the dm-po2z target and not for other targets
>>> that uses npo2 zoned devices (like dm-linear). So to perform this
>>> operation in a target independent way in dm-zone.c, I chose to always
>>> revalidate npo2 zoned device and update the chunk sector and nr_zones in
>>> dm_zone_revalidate_cb based on the zone information from the target.
>>> This allows to set the limits correctly for dm-po2z target.
>>
>> But DM revalidate will be called for the target AFTER it is setup (after
>> its gendisk is added). So how can DM revalidate see the incorrect zone
>> size ? If that is the case, then the target constructor is broken or
>> missing something. DM revalidate zone is generic and only allocates the
>> zone bitmaps for the target device. There should be not need at all to
>> touch that function.
>>
> I think this is a cleaner approach using features flag and io_hints
> instead of messing with the revalidate zone function:
> 
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 135c0cc190fb..c97a71e0473f 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -1618,6 +1618,9 @@ static int device_not_matches_zone_sectors(struct
> dm_target *ti, struct dm_dev *
>  	if (!blk_queue_is_zoned(q))
>  		return 0;
> 
> +	if(dm_target_supports_emulated_zone_size(ti->type))
> +		return 0;
> +

This should be in validate_hardware_zoned_model(), not here.

>  	return blk_queue_zone_sectors(q) != *zone_sectors;
>  }
> 
> diff --git a/drivers/md/dm-zoned-npo2-target.c
> b/drivers/md/dm-zoned-npo2-target.c
> index dad135964e09..b203be808f09 100644
> --- a/drivers/md/dm-zoned-npo2-target.c
> +++ b/drivers/md/dm-zoned-npo2-target.c
> @@ -187,6 +187,12 @@ static int dmz_npo2_end_io(struct dm_target *ti,
> struct bio *bio,
>  	return DM_ENDIO_DONE;
>  }
> 
> +static void dmz_npo2_io_hints(struct dm_target *ti, struct queue_limits
> *limits)
> +{
> +	struct dmz_npo2_target *dmh = ti->private;
> +	limits->chunk_sectors = dmh->zsze_po2;
> +}
> +
>  static int dmz_npo2_map(struct dm_target *ti, struct bio *bio)
>  {
>  	struct dmz_npo2_target *dmh = ti->private;
> @@ -233,12 +239,13 @@ static int dmz_npo2_iterate_devices(struct
> dm_target *ti,
>  static struct target_type dmz_npo2_target = {
>  	.name = "zoned-npo2",
>  	.version = { 1, 0, 0 },
> -	.features = DM_TARGET_ZONED_HM,
> +	.features = DM_TARGET_ZONED_HM | DM_TARGET_EMULATED_ZONE_SIZE,
>  	.map = dmz_npo2_map,
>  	.end_io = dmz_npo2_end_io,
>  	.report_zones = dmz_npo2_report_zones,
>  	.iterate_devices = dmz_npo2_iterate_devices,
>  	.module = THIS_MODULE,
> +	.io_hints = dmz_npo2_io_hints,
>  	.ctr = dmz_npo2_ctr,
>  };
> 
> diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
> index c2a3758c4aaa..9f3a4d98a22a 100644
> --- a/include/linux/device-mapper.h
> +++ b/include/linux/device-mapper.h
> @@ -283,6 +283,15 @@ struct target_type {
>  #define dm_target_supports_mixed_zoned_model(type) (false)
>  #endif
> 
> +#ifdef CONFIG_BLK_DEV_ZONED
> +#define DM_TARGET_EMULATED_ZONE_SIZE	0x00000400

Make it general: DM_TARGET_EMULATED_ZONES

> +#define dm_target_supports_emulated_zone_size(type) \
> +	((type)->features & DM_TARGET_EMULATED_ZONE_SIZE)
> +#else
> +#define DM_TARGET_EMULATED_ZONE_SIZE	0x00000000
> +#define dm_target_supports_emulated_zone_size(type) (false)
> +#endif
> +
>  struct dm_target {
>  	struct dm_table *table;
>  	struct target_type *type;
> 

-- 
Damien Le Moal
Western Digital Research