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Tue, 15 Mar 2022 17:46:49 -0700 (PDT) Received: from [10.225.163.101] (unknown [10.225.163.101]) by usg-ed-osssrv.wdc.com (Postfix) with ESMTPSA id 4KJBRp3g6sz1Rvlx; Tue, 15 Mar 2022 17:46:46 -0700 (PDT) Message-ID: Date: Wed, 16 Mar 2022 09:46:44 +0900 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.2 Subject: Re: [PATCH 0/6] power_of_2 emulation support for NVMe ZNS devices Content-Language: en-US To: Luis Chamberlain Cc: Christoph Hellwig , =?UTF-8?Q?Javier_Gonz=c3=a1lez?= , =?UTF-8?Q?Matias_Bj=c3=b8rling?= , Keith Busch , Pankaj Raghav , Adam Manzanares , "jiangbo.365@bytedance.com" , kanchan Joshi , Jens Axboe , Sagi Grimberg , Pankaj Raghav , Kanchan Joshi , "linux-block@vger.kernel.org" , "linux-nvme@lists.infradead.org" References: <20220314104938.hv26bf5vah4x32c2@ArmHalley.local> <20220314195551.sbwkksv33ylhlyx2@ArmHalley.local> <20220315130501.q7fjpqzutadadfu3@ArmHalley.localdomain> <20220315132611.g5ert4tzuxgi7qd5@unifi> <20220315133052.GA12593@lst.de> <62ed2891-f4b2-d63c-553d-8cae49b586bc@opensource.wdc.com> From: Damien Le Moal Organization: Western Digital Research In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220315_174651_025673_A18DD5C1 X-CRM114-Status: GOOD ( 28.82 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On 3/16/22 09:23, Luis Chamberlain wrote: > On Wed, Mar 16, 2022 at 09:07:18AM +0900, Damien Le Moal wrote: >> On 3/16/22 02:00, Luis Chamberlain wrote: >>> On Tue, Mar 15, 2022 at 02:30:52PM +0100, Christoph Hellwig wrote: >>>> On Tue, Mar 15, 2022 at 02:26:11PM +0100, Javier Gonz=C3=A1lez wrote= : >>>>> but we do not see a usage for ZNS in F2FS, as it is a mobile >>>>> file-system. As other interfaces arrive, this work will become natu= ral. >>>>> >>>>> ZoneFS and butrfs are good targets for ZNS and these we can do. I w= ould >>>>> still do the work in phases to make sure we have enough early feedb= ack >>>>> from the community. >>>>> >>>>> Since this thread has been very active, I will wait some time for >>>>> Christoph and others to catch up before we start sending code. >>>> >>>> Can someone summarize where we stand? >>> >>> RFCs should be posted to help review and evaluate direct NPO2 support >>> (not emulation) given we have no vendor willing to take a position th= at >>> NPO2 will *never* be supported on ZNS, and its not clear yet how many >>> vendors other than Samsung actually require NPO2 support. The other >>> reason is existing NPO2 customers currently cake in hacks to Linux to >>> supoport NPO2 support, and so a fragmentation already exists. To help >>> address this it's best to evaluate what the world of NPO2 support wou= ld >>> look like and put the effort to do the work for that and review that. >> >> And again no mentions of all the applications supporting zones assumin= g >> a power of 2 zone size that will break. >=20 > What applications? ZNS does not incur a PO2 requirement. So I really > want to know what applications make this assumption and would break > because all of a sudden say NPO2 is supported. Exactly. What applications ? For ZNS, I cannot say as devices have not been available for long. But neither can you. > Why would that break those ZNS applications? Please keep in mind that there are power of 2 zone sized ZNS devices out there. Applications designed for these devices and optimized to do bit shift arithmetic using the power of 2 size property will break. What the plan for that case ? How will you address these users complaints ? >> Allowing non power of 2 zone size may prevent applications running tod= ay >> to run properly on these non power of 2 zone size devices. *not* nice. >=20 > Applications which want to support ZNS have to take into consideration > that NPO2 is posisble and there existing users of that world today. Which is really an ugly approach. The kernel zone user interface is common to all zoned devices: SMR, ZNS, null_blk, DM (dm-crypt, dm-linear). They all have one point in common: zone size is a power of 2. Zone capacity may differ, but hey, we also unified that by reporting a zone capacity for *ALL* of them. Applications correctly designed for SMR can thus also run on ZNS too. With this in mind, the spectrum of applications that would break on non power of 2 ZNS devices is suddenly much larger. This has always been my concern from the start: allowing non power of 2 zone size fragments userspace support and has the potential to complicate things for application developers. >=20 > You cannot negate their existance. >=20 >> I have yet to see any convincing argument proving that this is not an = issue. >=20 > You are just saying things can break but not clarifying exactly what. > And you have not taken a position to say WD will not ever support NPO2 > on ZNS. And so, you can't negate the prospect of that implied path for > support as a possibility, even if it means work towards the ecosystem > today. Please do not bring in corporate strategy aspects in this discussion. This is a technical discussion and I am not talking as a representative of my employer nor should we ever dicsuss business plans on a public mailing list. I am a kernel developer and maintainer. Keep it technical please. --=20 Damien Le Moal Western Digital Research