Re: [LSF/MM/BPF BoF] BoF for Zoned Storage

Javier González
2022-03-11T07:21:09Z

On 08.03.2022 05:42, Damien Le Moal wrote:
>On 3/8/22 00:15, Keith Busch wrote:
>> On Mon, Mar 07, 2022 at 03:35:12PM +0100, Javier González wrote:
>>> As I mentioned in the last reply to to Dave, the main concern for me
>>> at the moment is supporting arbitrary zone sizes in the kernel. If we
>>> can agree on a path towards that, we can definitely commit to focus on
>>> ZoneFS and implement support for it on the different places we
>>> maintain in user-space.
>>
>> FWIW, the block layer doesn't require pow2 chunk_sectors anymore, so it
>> looks like that requirement for zone sizes can be relaxed, too.
>
>As long as:
>1) Userspace does not break (really not sure about that one...)
>2) No performance regression: the overhead of using multiplications &
>divisions for sector to zone conversions must be acceptable for ZNS (it
>will not matter for SMR HDDs)

Good. The emulation patches we sent should cover this.

>All in kernel users of zoned devices will need some patching (zonefs,
>btrfs, f2fs). Some will not work anymore (e.g. f2fs) and others will
>need different constraints (btrfs needs 64K aligned zones). Not all
>zoned devices will be usable anymore, and I am not sure if this
>degradation in the support provided is acceptable.

We will do the work for btrfs (already have a prototype) and for zonefs
(we need to look into it). F2FS will use the emulation layer for now;
only !PO2 devices will pay the price. We will add a knob in the block
layer so that F2FS can force enable the emulation.