linux-kernel - Re: [PATCH 2/2] nvme: add emulation for zone-append

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Date:   Thu, 20 Aug 2020 08:37:19 +0200
From:   Javier Gonzalez <javier@...igon.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     david.fugate@...ux.intel.com, Christoph Hellwig <hch@....de>,
        Kanchan Joshi <joshi.k@...sung.com>,
        "kbusch@...nel.org" <kbusch@...nel.org>,
        "Damien.LeMoal@....com" <Damien.LeMoal@....com>,
        "sagi@...mberg.me" <sagi@...mberg.me>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "johannes.thumshirn@....com" <johannes.thumshirn@....com>,
        Nitesh Shetty <nj.shetty@...sung.com>,
        SelvaKumar S <selvakuma.s1@...sung.com>
Subject: Re: [PATCH 2/2] nvme: add emulation for zone-append

On 19.08.2020 13:25, Jens Axboe wrote:
>On 8/19/20 12:11 PM, David Fugate wrote:
>> On Tue, 2020-08-18 at 07:12 +0000, Christoph Hellwig wrote:
>>> On Tue, Aug 18, 2020 at 10:59:36AM +0530, Kanchan Joshi wrote:
>>>> If drive does not support zone-append natively, enable emulation
>>>> using
>>>> regular write.
>>>> Make emulated zone-append cmd write-lock the zone, preventing
>>>> concurrent append/write on the same zone.
>>>
>>> I really don't think we should add this.  ZNS and the Linux support
>>> were all designed with Zone Append in mind, and then your company did
>>> the nastiest possible move violating the normal NVMe procedures to
>>> make
>>> it optional.  But that doesn't change the fact the Linux should keep
>>> requiring it, especially with the amount of code added here and how
>>> it
>>> hooks in the fast path.
>>
>> Intel does not support making *optional* NVMe spec features *required*
>> by the NVMe driver.
>
>It's not required, the driver will function quite fine without it. If you
>want to use ZNS it's required. The Linux driver thankfully doesn't need
>any vendor to sign off on what it can or cannot do, or what features
>are acceptable.
>
>> It's forgivable WDC's accepted contribution didn't work with other
>> vendors' devices choosing not to implement the optional Zone Append,
>> but it's not OK to reject contributions remedying this.  Provided
>> there's no glaring technical issues, Samsung's contribution should be
>> accepted to maintain both spec compliance as well as vendor neutrality.
>
>It's *always* ok to reject contributions, if those contributions cause
>maintainability issues, unacceptable slowdowns, or whatever other issue
>that the maintainers of said driver don't want to deal with. Any
>contribution should be judged on merit, not based on political decisions
>or opinions. Obviously this thread reeks of it.
>

I'll reply here, where the discussion diverges from this particular
patch.

We will stop pushing for this emulation. We have a couple of SSDs where
we disabled Append, we implemented support for them, and we wanted to
push the changes upstream. That's it. This is no politics not a
conspiracy against the current ZNS spec. We spent a lot of time working
on this spec and are actually doing a fair amount of work to support
Append other places in the stack. In any case, the fuzz stops here.

Javier