Re: [PATCH v4 0/1] Enforce 4k sectorize by default for mkfs

[Josef Bacik <josef@toxicpanda.com>]

On Thu, Nov 16, 2023 at 11:02:23AM -0500, Neal Gompa wrote:
> The Fedora Asahi SIG[0] is working on bringing up support for
> Apple Silicon Macintosh computers through the Fedora Asahi Remix[1].
> 
> Apple Silicon Macs are unusual in that they currently require 16k
> page sizes, which means that the current default for mkfs.btrfs(8)
> makes a filesystem that is unreadable on x86 PCs and most other ARM
> PCs.
> 
> This is now even more of a problem within Apple Silicon Macs as it is now
> possible to nest 4K Fedora Linux VMs on 16K Fedora Asahi Remix machines to
> enable performant x86 emulation[2] and the host storage needs to be compatible
> for both environments.
> 
> Thus, I'd like to see us finally make the switchover to 4k sectorsize
> for new filesystems by default, regardless of page size.
> 
> The initial test run by Hector Martin[3] at request of Qu Wenruo
> looked promising[4], and we've been running with this behavior on
> Fedora Linux since Fedora Linux 36 (at around 6.2) with no issues.
> 

This is a good change and well documented.  This isn't being ignored, it's just
a policy change that we have to be conservative about considering.  We only in
the last 3 months have added a Apple Silicon machine to our testing
infrastructure (running Fedora Asahi fwiw) to make sure we're getting consistent
subpage-blocksize testing.  Generally speaking it's been fine, we've fixed a few
things and haven't broken anything, but it's still comes with some risks when
compared to the default of using the pagesize.

We will continue to discuss this amongst ourselves and figure out what we think
would be a reasonable timeframe to make this switch and let you know what we're
thinking ASAP.  Thanks,

Josef