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Date:   Fri, 30 Sep 2022 19:14:21 -0700
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Subject: Re: [PATCH v15 00/13] support zoned block devices with non-power-of-2
 zone sizes
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To:     Damien Le Moal <damien.lemoal@opensource.wdc.com>,
        Jens Axboe <axboe@kernel.dk>,
        Pankaj Raghav <p.raghav@samsung.com>, hch@lst.de,
        Keith Busch <kbusch@kernel.org>
Cc:     jaegeuk@kernel.org, agk@redhat.com, gost.dev@samsung.com,
        snitzer@kernel.org, linux-kernel@vger.kernel.org, hare@suse.de,
        matias.bjorling@wdc.com, Johannes.Thumshirn@wdc.com,
        linux-block@vger.kernel.org, linux-nvme@lists.infradead.org,
        pankydev8@gmail.com, dm-devel@redhat.com,
        "Martin K. Petersen" <martin.petersen@oracle.com>
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 <bb2b3784-422f-fc82-e5be-e4d24412e21f@opensource.wdc.com>
From:   Bart Van Assche <bvanassche@acm.org>
In-Reply-To: <bb2b3784-422f-fc82-e5be-e4d24412e21f@opensource.wdc.com>
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On 9/30/22 17:45, Damien Le Moal wrote:
> On 10/1/22 04:38, Bart Van Assche wrote:
>> Since this has not been mentioned in the cover letter, I want to add
>> that in the near future we will need these patches for Android devices.
>> JEDEC is working on supporting zoned storage for UFS devices, the
>> storage devices used in all modern Android phones. Although it would be
>> possible to make the offset between zone starts a power of two by
>> inserting gap zones between data zones, UFS vendors asked not to do this
>> and hence need support for zone sizes that are not a power of two. An
>> advantage of not having to deal with gap zones is better filesystem
>> performance since filesystem extents cannot span gap zones. Having to
>> split filesystem extents because of gap zones reduces filesystem
>> performance.
> 
> As mentioned many times, my opinion is that a good implementation should
> *not* have any extent span zone boundaries. So personally, I do not
> consider such argument as a valid justification for the non-power-of-2
> zone size support.

Hi Damien,

Although the filesystem extent issue probably can be solved in software, 
the argument that UFS vendors strongly prefer not to have gap zones and 
hence need support for zone sizes that are not a power of two remains.

Thanks,

Bart.