Re: [dm-devel] [PATCH v15 00/13] support zoned block devices with non-power-of-2 zone sizes

From: Can Guo <quic_cang@quicinc.com>
To: Pankaj Raghav <p.raghav@samsung.com>, <snitzer@kernel.org>,
	<axboe@kernel.dk>, <agk@redhat.com>, <hch@lst.de>,
	<damien.lemoal@opensource.wdc.com>
Cc: bvanassche@acm.org, pankydev8@gmail.com, gost.dev@samsung.com,
	linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
	linux-block@vger.kernel.org, dm-devel@redhat.com,
	Johannes.Thumshirn@wdc.com, jaegeuk@kernel.org,
	matias.bjorling@wdc.com
Subject: Re: [dm-devel] [PATCH v15 00/13] support zoned block devices with non-power-of-2 zone sizes
Date: Wed, 4 Jan 2023 13:29:37 +0800	[thread overview]
Message-ID: <3b4e4a73-7870-750a-8a39-58735843b0aa@quicinc.com> (raw)
In-Reply-To: <20220923173618.6899-1-p.raghav@samsung.com>

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Hi Pankaj,

On 9/24/2022 1:36 AM, Pankaj Raghav wrote:
> Hi Jens,
>    Please consider this patch series for the 6.1 release.
>
> - Background and Motivation:
>
> The zone storage implementation in Linux, introduced since v4.10, first
> targetted SMR drives which have a power of 2 (po2) zone size alignment
> requirement. The po2 zone size was further imposed implicitly by the
> block layer's blk_queue_chunk_sectors(), used to prevent IO merging
> across chunks beyond the specified size, since v3.16 through commit
> 762380ad9322 ("block: add notion of a chunk size for request merging").
> But this same general block layer po2 requirement for blk_queue_chunk_sectors()
> was removed on v5.10 through commit 07d098e6bbad ("block: allow 'chunk_sectors'
> to be non-power-of-2").
>
> NAND, which is the media used in newer zoned storage devices, does not
> naturally align to po2. In these devices, zone capacity(cap) is not the
> same as the po2 zone size. When the zone cap != zone size, then unmapped
> LBAs are introduced to cover the space between the zone cap and zone size.
> po2 requirement does not make sense for these type of zone storage devices.
> This patch series aims to remove these unmapped LBAs for zoned devices when
> zone cap is npo2. This is done by relaxing the po2 zone size constraint
> in the kernel and allowing zoned device with npo2 zone sizes if zone cap
> == zone size.

I came across function sd_zbc_check_capacity() in sd_zbc.c, it still 
errors out in case of npo2.

I don't see this series touching sd_zbc.c. Is there plan or existing 
change to relax this check?

if(!*is_power_of_2* 
<https://elixir.bootlin.com/linux/v6.2-rc2/C/ident/is_power_of_2>(*zone_blocks* 
<https://elixir.bootlin.com/linux/v6.2-rc2/C/ident/zone_blocks>)){

*sd_printk* 
<https://elixir.bootlin.com/linux/v6.2-rc2/C/ident/sd_printk>(*KERN_ERR* 
<https://elixir.bootlin.com/linux/v6.2-rc2/C/ident/KERN_ERR>,sdkp,

"Zone size %llu is not a power of two.\n",

*zone_blocks* 
<https://elixir.bootlin.com/linux/v6.2-rc2/C/ident/zone_blocks>);

return-*EINVAL* <https://elixir.bootlin.com/linux/v6.2-rc2/C/ident/EINVAL>;

}

Thanks.

Regards,

Can Guo.

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