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

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Message-ID: <20200818181124.2ys5urtkodpkamsr@MacBook-Pro.localdomain>
Date:   Tue, 18 Aug 2020 20:11:24 +0200
From:   Javier Gonzalez <javier@...igon.com>
To:     Matias Bjørling <mb@...htnvm.io>
Cc:     Christoph Hellwig <hch@....de>, axboe@...nel.dk,
        Damien.LeMoal@....com, SelvaKumar S <selvakuma.s1@...sung.com>,
        sagi@...mberg.me, Kanchan Joshi <joshi.k@...sung.com>,
        johannes.thumshirn@....com, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, kbusch@...nel.org,
        Nitesh Shetty <nj.shetty@...sung.com>
Subject: Re: [PATCH 2/2] nvme: add emulation for zone-append

On 18.08.2020 12:51, Matias Bjørling wrote:
>On 18/08/2020 11.50, Javier Gonzalez wrote:
>>On 18.08.2020 09:12, 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.
>>
>>I understand that the NVMe process was agitated and that the current ZNS
>>implementation in Linux relies in append support from the device
>>perspective. However, the current TP does allow for not implementing
>>append, and a number of customers are requiring the use of normal
>>writes, which we want to support.
>
>There is a lot of things that is specified in NVMe, but not 
>implemented in the Linux kernel. That your company is not able to 
>efficiently implement the Zone Append command (this is the only reason 
>I can think of that make you and your company cause such a fuss), 

This comment is out of place and I will choose to ignore it.

>shouldn't mean that everyone else has to suffer.

This is not a quirk, nor a software work-around, This is a design
decision affecting the storage stack of several OEMs. As such, I would
like to find a way to implement this functionality.

Last time we discussed this in the mailing list, you among others
pointed to append emulation as the best way to enable this path and here
we are. Can you explained what changed?

>
>In any case, SPDK offers adequate support and can be used today.

We take the SPDK discussion in the appropriate mailing lists and slack
channels.