[PATCH 0/6] power_of_2 emulation support for NVMe ZNS devices

[Matias Bjørling]

> -----Original Message-----
> From: Javier González <javier at javigon.com>
> Sent: Tuesday, 15 March 2022 14.26
> To: Matias Bjørling <Matias.Bjorling at wdc.com>
> Cc: Damien Le Moal <damien.lemoal at opensource.wdc.com>; Christoph
> Hellwig <hch at lst.de>; Luis Chamberlain <mcgrof at kernel.org>; Keith Busch
> <kbusch at kernel.org>; Pankaj Raghav <p.raghav at samsung.com>; Adam
> Manzanares <a.manzanares at samsung.com>; jiangbo.365 at bytedance.com;
> kanchan Joshi <joshi.k at samsung.com>; Jens Axboe <axboe at kernel.dk>; Sagi
> Grimberg <sagi at grimberg.me>; Pankaj Raghav <pankydev8 at gmail.com>;
> Kanchan Joshi <joshiiitr at gmail.com>; linux-block at vger.kernel.org; linux-
> nvme at lists.infradead.org
> Subject: Re: [PATCH 0/6] power_of_2 emulation support for NVMe ZNS devices
> 
> On 15.03.2022 13:14, Matias Bjørling wrote:
> >> >
> >> >All that said - if there are people willing to do the work and it
> >> >doesn't have a
> >> negative impact on performance, code quality, maintenance complexity,
> etc.
> >> then there isn't anything saying support can't be added - but it does
> >> seem like it’s a lot of work, for little overall benefits to applications and the
> host users.
> >>
> >> Exactly.
> >>
> >> Patches in the block layer are trivial. This is running in production
> >> loads without issues. I have tried to highlight the benefits in
> >> previous benefits and I believe you understand them.
> >>
> >> Support for ZoneFS seems easy too. We have an early POC for btrfs and
> >> it seems it can be done. We sign up for these 2.
> >>
> >> As for F2FS and dm-zoned, I do not think these are targets at the
> >> moment. If this is the path we follow, these will bail out at mkfs time.
> >>
> >> If we can agree on the above, I believe we can start with the code
> >> that enables the existing customers and build support for butrfs and
> >> ZoneFS in the next few months.
> >>
> >> What do you think?
> >
> >I would suggest to do it in a single shot, i.e., a single patchset, which enables
> all the internal users in the kernel (including f2fs and others). That way end-
> users do not have to worry about the difference of PO2/NPO2 zones and it'll
> help reduce the burden on long-term maintenance.
> 
> Thanks for the suggestion Matias. Happy to see that you are open to support
> this. I understand why a patchseries fixing all is attracgive, 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 natural.

We've seen uptake on ZNS on f2fs, so I would argue that its important to have support in as well.

> 
> ZoneFS and butrfs are good targets for ZNS and these we can do. I would still do
> the work in phases to make sure we have enough early feedback from the
> community.

Sure, continuous review is good. But not having support for all the kernel users creates fragmentation. Doing a full switch is greatly preferred, as it avoids this fragmentation, but will also lower the overall maintenance burden, which also was raised as a concern.