Re: [PATCH 36/43] xfs: disable reflink for zoned file systems

Darrick J. Wong
2024-12-17T17:10:56Z

On Sun, Dec 15, 2024 at 07:26:54AM +0100, Christoph Hellwig wrote:
> On Fri, Dec 13, 2024 at 03:12:47PM -0800, Darrick J. Wong wrote:
> > On Wed, Dec 11, 2024 at 09:55:01AM +0100, Christoph Hellwig wrote:
> > > While the zoned on-disk format supports reflinks, the GC code currently
> > > always unshares reflinks when moving blocks to new zones, thus making the
> > > feature unusuable. Disable reflinks until the GC code is refcount aware.
> >
> > This goes back to the question I had in the gc patch -- can we let
> > userspace do its own reflink-aware freespace copygc, and only use the
> > in-kernel gc if userspace doesn't respond fast enough? I imagine
> > someone will want to share used blocks on zoned storage at some point.
>
> I'm pretty sure we could, if we're willing to deal with worse decision
> making, worse performance and potential for deadlocks while dealing with
> a bigger and more complicated code base. But why?

Mostly intellectual curiosity on my part about self-reorganizing
filesystems. The zonegc you've already written is good enough for now,
though the no-reflink requirement feels a bit onerous.

But hey, it's not like I have numbers showing that a userspace
copy-dedupe gc strategy is any better, so I'll not hold up this whole
series on account of that.

--D