Re: [PATCH 2/5] null_blk: introduce zone capacity for zoned device

From: Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com>
To: Keith Busch <Keith.Busch@wdc.com>,
	"linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
Cc: Damien Le Moal <Damien.LeMoal@wdc.com>,
	Matias Bjorling <Matias.Bjorling@wdc.com>,
	Christoph Hellwig <hch@lst.de>, Sagi Grimberg <sagi@grimberg.me>,
	Jens Axboe <axboe@kernel.dk>,
	Aravind Ramesh <Aravind.Ramesh@wdc.com>
Subject: Re: [PATCH 2/5] null_blk: introduce zone capacity for zoned device
Date: Mon, 15 Jun 2020 23:46:25 +0000	[thread overview]
Message-ID: <BYAPR04MB4965573D0109F13F1E6BA8D1869C0@BYAPR04MB4965.namprd04.prod.outlook.com> (raw)
In-Reply-To: 20200615233424.13458-3-keith.busch@wdc.com

Apart from couple of nits this looks good.

Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>

On 6/15/20 4:35 PM, Keith Busch wrote:

> From: Aravind Ramesh <aravind.ramesh@wdc.com>
> 
> Allow emulation of a zoned device with a per zone capacity smaller than
> the zone size as as defined in the Zoned Namespace (ZNS) Command Set
> specification. The zone capacity defaults to the zone size if not
> specified and must be smaller than the zone size otherwise.
> 
> Signed-off-by: Aravind Ramesh <aravind.ramesh@wdc.com>
> ---
>   drivers/block/null_blk.h       |  2 ++
>   drivers/block/null_blk_main.c  |  9 ++++++++-
>   drivers/block/null_blk_zoned.c | 17 +++++++++++++++--
>   3 files changed, 25 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/block/null_blk.h b/drivers/block/null_blk.h
> index 81b311c9d781..7eadf190528c 100644
> --- a/drivers/block/null_blk.h
> +++ b/drivers/block/null_blk.h
> @@ -44,11 +44,13 @@ struct nullb_device {
>   	unsigned int nr_zones;
>   	struct blk_zone *zones;
>   	sector_t zone_size_sects;
> +	sector_t zone_capacity_sects;
>   
>   	unsigned long size; /* device size in MB */
>   	unsigned long completion_nsec; /* time in ns to complete a request */
>   	unsigned long cache_size; /* disk cache size in MB */
>   	unsigned long zone_size; /* zone size in MB if device is zoned */
> +	unsigned long zone_capacity; /* zone cap in MB if device is zoned */
>   	unsigned int zone_nr_conv; /* number of conventional zones */
>   	unsigned int submit_queues; /* number of submission queues */
>   	unsigned int home_node; /* home node for the device */
> diff --git a/drivers/block/null_blk_main.c b/drivers/block/null_blk_main.c
> index 87b31f9ca362..54c5b5df399d 100644
> --- a/drivers/block/null_blk_main.c
> +++ b/drivers/block/null_blk_main.c
> @@ -200,6 +200,10 @@ static unsigned long g_zone_size = 256;
>   module_param_named(zone_size, g_zone_size, ulong, S_IRUGO);
>   MODULE_PARM_DESC(zone_size, "Zone size in MB when block device is zoned. Must be power-of-two: Default: 256");
>   
> +static unsigned long g_zone_capacity;
> +module_param_named(zone_capacity, g_zone_capacity, ulong, 0444);
> +MODULE_PARM_DESC(zone_capacity, "Zone capacity in MB when block device is zoned. Can be less than or equal to zone size. Default: Zone size");
> +
>   static unsigned int g_zone_nr_conv;
>   module_param_named(zone_nr_conv, g_zone_nr_conv, uint, 0444);
>   MODULE_PARM_DESC(zone_nr_conv, "Number of conventional zones when block device is zoned. Default: 0");
> @@ -341,6 +345,7 @@ NULLB_DEVICE_ATTR(mbps, uint, NULL);
>   NULLB_DEVICE_ATTR(cache_size, ulong, NULL);
>   NULLB_DEVICE_ATTR(zoned, bool, NULL);
>   NULLB_DEVICE_ATTR(zone_size, ulong, NULL);
> +NULLB_DEVICE_ATTR(zone_capacity, ulong, NULL);
>   NULLB_DEVICE_ATTR(zone_nr_conv, uint, NULL);
>   
>   static ssize_t nullb_device_power_show(struct config_item *item, char *page)
> @@ -457,6 +462,7 @@ static struct configfs_attribute *nullb_device_attrs[] = {
>   	&nullb_device_attr_badblocks,
>   	&nullb_device_attr_zoned,
>   	&nullb_device_attr_zone_size,
> +	&nullb_device_attr_zone_capacity,
>   	&nullb_device_attr_zone_nr_conv,
>   	NULL,
>   };
> @@ -510,7 +516,7 @@ nullb_group_drop_item(struct config_group *group, struct config_item *item)
>   
>   static ssize_t memb_group_features_show(struct config_item *item, char *page)
>   {
> -	return snprintf(page, PAGE_SIZE, "memory_backed,discard,bandwidth,cache,badblocks,zoned,zone_size,zone_nr_conv\n");
> +	return snprintf(page, PAGE_SIZE, "memory_backed,discard,bandwidth,cache,badblocks,zoned,zone_size,zone_capacity,zone_nr_conv\n");
This line is becoming ridiculously long even for new 100 char limit. 
Maybe we should do a cleanup patch for feature to string conversion.
>   }
>   
>   CONFIGFS_ATTR_RO(memb_group_, features);
> @@ -571,6 +577,7 @@ static struct nullb_device *null_alloc_dev(void)
>   	dev->use_per_node_hctx = g_use_per_node_hctx;
>   	dev->zoned = g_zoned;
>   	dev->zone_size = g_zone_size;
> +	dev->zone_capacity = g_zone_capacity;
>   	dev->zone_nr_conv = g_zone_nr_conv;
>   	return dev;
>   }
> diff --git a/drivers/block/null_blk_zoned.c b/drivers/block/null_blk_zoned.c
> index 624aac09b005..b05832eb21b2 100644
> --- a/drivers/block/null_blk_zoned.c
> +++ b/drivers/block/null_blk_zoned.c
> @@ -28,7 +28,17 @@ int null_init_zoned_dev(struct nullb_device *dev, struct request_queue *q)
>   		return -EINVAL;
>   	}
>   
> +	if (!dev->zone_capacity)
> +		dev->zone_capacity = dev->zone_size;
> +
> +	if (dev->zone_capacity > dev->zone_size) {
> +		pr_err("null_blk: zone capacity %lu more than its size %lu\n",
> +					dev->zone_capacity, dev->zone_size);
> +		return -EINVAL;
> +	}
> +
>   	dev->zone_size_sects = dev->zone_size << ZONE_SIZE_SHIFT;
> +	dev->zone_capacity_sects = dev->zone_capacity << ZONE_SIZE_SHIFT;
Do we really need zone_capacity_sects ? As far as I can see its is not 
used into fast path, correct me if I'm wrong.
>   	dev->nr_zones = dev_size >>
>   				(SECTOR_SHIFT + ilog2(dev->zone_size_sects));
>   	dev->zones = kvmalloc_array(dev->nr_zones, sizeof(struct blk_zone),
> @@ -60,7 +70,7 @@ int null_init_zoned_dev(struct nullb_device *dev, struct request_queue *q)
>   
>   		zone->start = zone->wp = sector;
>   		zone->len = dev->zone_size_sects;
> -		zone->capacity = zone->len;
> +		zone->capacity = dev->zone_capacity_sects;
We can just dev->zone_capacity << ZONE_SIZE_SHIFT here.
>   		zone->type = BLK_ZONE_TYPE_SEQWRITE_REQ;
>   		zone->cond = BLK_ZONE_COND_EMPTY;
>   
> @@ -187,6 +197,9 @@ static blk_status_t null_zone_write(struct nullb_cmd *cmd, sector_t sector,
>   			return BLK_STS_IOERR;
>   		}
>   
> +		if (zone->wp + nr_sectors > zone->start + zone->capacity)
> +			return BLK_STS_IOERR;
> +
>   		if (zone->cond != BLK_ZONE_COND_EXP_OPEN)
>   			zone->cond = BLK_ZONE_COND_IMP_OPEN;
>   
> @@ -195,7 +208,7 @@ static blk_status_t null_zone_write(struct nullb_cmd *cmd, sector_t sector,
>   			return ret;
>   
>   		zone->wp += nr_sectors;
> -		if (zone->wp == zone->start + zone->len)
> +		if (zone->wp == zone->start + zone->capacity)
>   			zone->cond = BLK_ZONE_COND_FULL;
>   		return BLK_STS_OK;
>   	default:
> 