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

[Damien Le Moal <damien.lemoal@opensource.wdc.com>]

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)

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.

-- 
Damien Le Moal
Western Digital Research