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

Damien Le Moal
2022-03-11T07:39:20Z

On 3/11/22 16:21, Javier González wrote:
> 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.

No. The FS has no business changing the device.

--
Damien Le Moal
Western Digital Research