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

[Pankaj Raghav <p.raghav@samsung.com>]

On 2022-03-10 10:47, Christoph Hellwig wrote:
> This is complete bonkers.  IFF we have a good reason to support non
> power of two zones size (and I'd like to see evidence for that) we'll

non power of 2 support is important to the users and that is why we
started this effort to do that. I have also CCed Bo from Bytedance based
on their request.

> need to go through all the layers to support it.  But doing this emulation
> is just idiotic and will at tons of code just to completely confuse users.
> 

I agree with your point to create the non power of 2 support through all
the layers but this is the first step.

One of the early feedback that we got from Damien is to not break the
existing kernel and userspace applications that are written with the po2
assumption.

The following are the steps we have in the pipeline:
- Remove the constraint in the block layer
- Start migrating the Kernel applications such as btrfs so that it also
works on non power of 2 devices.

Of course, we wanted to post RFCs to the steps mentioned above so that
there could be a public discussion about the issues.

> Well, apparently whoever produces these drives never cared about supporting
> Linux as the power of two requirement goes back to SMR HDDs, which also
> don't have that requirement in the spec (and even allow non-uniform zone
> size), but Linux decided that we want this for sanity.
> 
> Do these drives even support Zone Append?

Yes, these drives are intended for Linux users that would use the zoned
block device. Append is supported but holes in the LBA space (due to
diff in zone cap and zone size) is still a problem for these users.
-- 
Regards,
Pankaj