linux-kernel - Re: Please further explain Linux's "zoned storage" roadmap [was: Re: [PATCH v14 00/13] support zoned block devices with non-power-of-2 zone sizes]

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Message-ID: <b393c127-b773-8296-a559-83606077aa1c@samsung.com>
Date:   Thu, 22 Sep 2022 13:53:02 +0200
From:   Pankaj Raghav <p.raghav@...sung.com>
To:     Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Mike Snitzer <snitzer@...hat.com>, <axboe@...nel.dk>,
        <hch@....de>, Keith Busch <kbusch@...nel.org>
CC:     <agk@...hat.com>, <snitzer@...nel.org>, <bvanassche@....org>,
        <pankydev8@...il.com>, <gost.dev@...sung.com>,
        <linux-kernel@...r.kernel.org>, <linux-nvme@...ts.infradead.org>,
        <linux-block@...r.kernel.org>, <dm-devel@...hat.com>,
        <Johannes.Thumshirn@....com>, <jaegeuk@...nel.org>,
        <matias.bjorling@....com>
Subject: Re: Please further explain Linux's "zoned storage" roadmap [was:
 Re: [PATCH v14 00/13] support zoned block devices with non-power-of-2 zone
 sizes]

Thanks a lot Damien for the summary. Your feedback has made this series
much better.

> Pankaj patch series is all about supporting ZNS devices that have a zone
> size that is not a power of 2 number of LBAs as some vendors want to
> produce such drives. There is no such move happening in the SMR world as
> all users are happy with the current zone sizes which match the kernel
> support (which currently requires power-of-2 number of LBAs for the zone
> size).
> 
> I do not think we have yet reached a consensus on if we really want to
> accept any zone size for zoned storage. I personally am not a big fan of
> removing the existing constraint as that makes the code somewhat heavier
> (multiplication & divisions instead of bit shifts) without introducing any
> benefit to the user that I can see (or agree with). And there is also a
> risk of forcing onto the users to redesign/change their code to support
> different devices in the same system. That is never nice to fragment
> support like this for the same device class. This is why several people,
> including me, requested something like dm-po2zoned, to avoid breaking user
> applications if non-power-of-2 zone size drives support is merged. Better
> than nothing for sure, but not ideal either. That is only my opinion.
> There are different opinions out there.

I appreciate that you have explained the different perspectives. We have
covered this written and orally, and it seems to me that we have a good
coverage of the arguments in the list.

At this point, I would like to ask the opinion of Jens, Christoph and
Keith. Do you think we are missing anything in the series? Can this be
queued up for 6.1 (after I send the next version with a minor fix suggested
by Mike)?

--
Regards,
Pankaj