Re: [PATCH 5/5] nvme: support for zoned namespaces

From: "Javier González" <javier@javigon.com>
To: "Matias Bjørling" <mb@lightnvm.io>
Cc: "Jens Axboe" <axboe@kernel.dk>,
	"Niklas Cassel" <niklas.cassel@wdc.com>,
	"Damien Le Moal" <damien.lemoal@wdc.com>,
	"Ajay Joshi" <ajay.joshi@wdc.com>,
	"Sagi Grimberg" <sagi@grimberg.me>,
	"Keith Busch" <keith.busch@wdc.com>,
	"Dmitry Fomichev" <dmitry.fomichev@wdc.com>,
	"Aravind Ramesh" <aravind.ramesh@wdc.com>,
	linux-nvme@lists.infradead.org, linux-block@vger.kernel.org,
	"Hans Holmberg" <hans.holmberg@wdc.com>,
	"Judy Brock" <judy.brock@samsung.com>,
	"Christoph Hellwig" <hch@lst.de>,
	"Matias Bjørling" <matias.bjorling@wdc.com>
Subject: Re: [PATCH 5/5] nvme: support for zoned namespaces
Date: Wed, 17 Jun 2020 20:28:41 +0200	[thread overview]
Message-ID: <20200617182841.jnbxgshi7bawfzls@mpHalley.localdomain> (raw)
In-Reply-To: <f1bc34e0-c059-6127-d69f-e31c91ce6a9f@lightnvm.io>

On 17.06.2020 19:57, Matias Bjørling wrote:
>On 17/06/2020 16.42, Javier González wrote:
>>On 17.06.2020 09:43, Christoph Hellwig wrote:
>>>On Tue, Jun 16, 2020 at 12:41:42PM +0200, Javier González wrote:
>>>>On 16.06.2020 08:34, Keith Busch wrote:
>>>>>Add support for NVM Express Zoned Namespaces (ZNS) Command Set defined
>>>>>in NVM Express TP4053. Zoned namespaces are discovered based on their
>>>>>Command Set Identifier reported in the namespaces Namespace
>>>>>Identification Descriptor list. A successfully discovered Zoned
>>>>>Namespace will be registered with the block layer as a host managed
>>>>>zoned block device with Zone Append command support. A namespace that
>>>>>does not support append is not supported by the driver.
>>>>
>>>>Why are we enforcing the append command? Append is optional on the
>>>>current ZNS specification, so we should not make this mandatory in the
>>>>implementation. See specifics below.
>>>
>>>Because Append is the way to go and we've moved the Linux zoned block
>>>I/O stack to required it, as should have been obvious to anyone
>>>following linux-block in the last few months.  I also have to say I'm
>>>really tired of the stupid politics tha your company started in the
>>>NVMe working group, and will say that these do not matter for Linux
>>>development at all.  If you think it is worthwhile to support devices
>>>without Zone Append you can contribute support for them on top of this
>>>series by porting the SCSI Zone Append Emulation code to NVMe.
>>>
>>>And I'm not even going to read the rest of this thread as I'm on a
>>>vacation that I badly needed because of the Samsung TWG bullshit.
>>
>>My intention is to support some Samsung ZNS devices that will not enable
>>append. I do not think this is an unreasonable thing to do. How / why
>>append ended up being an optional feature in the ZNS TP is orthogonal to
>>this conversation. Bullshit or not, it ends up on devices that we would
>>like to support one way or another.
>
>I do not believe any of us have said that it is unreasonable to 
>support. We've only asked that you make the patches for it.
>
>All of us have communicated why Zone Append is a great addition to the 
>Linux kernel. Also, as Christoph points out, this has not been a 
>secret for the past couple of months, and as Martin pointed out, have 
>been a wanted feature for the past decade in the Linux community.

>
>I do want to politely point out, that you've got a very clear signal 
>from the key storage maintainers. Each of them is part of the planet's 
>best of the best and most well-respected software developers, that 
>literally have built the storage stack that most of the world depends 
>on. The storage stack that recently sent manned rockets into space. 
>They each unanimously said that the Zone Append command is the right 
>approach for the Linux kernel to reduce the overhead of I/O tracking 
>for zoned block devices. It may be worth bringing this information to 
>your engineering organization, and also potentially consider Zone 
>Append support for devices that you intend to used with the Linux 
>kernel storage stack.

I understand and I have never said the opposite. Append is a great
addition that we also have been working on for several months (see
patches additions from today). We just have a couple of use cases where
append is not required and I would like to make sure that they are
supported.

At the end of the day, the only thing I have disagreed on is that the
NVMe driver rejects ZNS SSDs that do not support append, as opposed to
doing this instead when an in-kernel user wants to utilize the drive
(e.g., formatting a FS with zoned support) This would allow _today_
ioctl() passthru to work for normal writes.

I still believe the above would be a more inclusive solution with the
current ZNS specification, but I can see that the general consensus is
different.

So we will go back, apply the feedback that we got and return with an
approach that better fits the ecosystem.

>
>Another approach, is to use SPDK, and bypass the Linux kernel. This 
>might even be an advantage, your customers does not have to wait on 
>the Linux distribution being released with a long term release, before 
>they can even get started and deploy in volume. I.e., they will 
>actually get faster to market, and your company will be able to sell 
>more drives.

I think I will refrain from discussing our business strategy on an open
mailing list. Appreciate the feedback though. Very insightful.

Thanks,
Javier

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