Re: [PATCH 2/2] xfs: disable large folio support in xfile_create

Darrick J. Wong
2024-02-08T16:04:12Z

On Wed, Feb 07, 2024 at 05:56:21PM -0800, Andrew Morton wrote:
> On Thu, 11 Jan 2024 18:22:50 -0800 "Darrick J. Wong" <djwong@kernel.org> wrote:
>
> > On Thu, Jan 11, 2024 at 10:45:53PM +0000, Matthew Wilcox wrote:
> > > On Thu, Jan 11, 2024 at 02:00:53PM -0800, Andrew Morton wrote:
> > > > On Wed, 10 Jan 2024 12:04:51 -0800 "Darrick J. Wong" <djwong@kernel.org> wrote:
> > > >
> > > > > > > Fixing this will require a bit of an API change, and prefeably sorting out
> > > > > > > the hwpoison story for pages vs folio and where it is placed in the shmem
> > > > > > > API. For now use this one liner to disable large folios.
> > > > > > >
> > > > > > > Reported-by: Darrick J. Wong <djwong@kernel.org>
> > > > > > > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > > > > >
> > > > > > Can someone who knows more about shmem.c than I do please review
> > > > > > https://lore.kernel.org/linux-xfs/20240103084126.513354-4-hch@lst.de/
> > > > > > so that I can feel slightly more confident as hch and I sort through the
> > > > > > xfile.c issues?
> > > > > >
> > > > > > For this patch,
> > > > > > Reviewed-by: Darrick J. Wong <djwong@kernel.org>
> > > > >
> > > > > ...except that I'm still getting 2M THPs even with this enabled, so I
> > > > > guess either we get to fix it now, or create our own private tmpfs mount
> > > > > so that we can pass in huge=never, similar to what i915 does. :(
> > > >
> > > > What is "this"? Are you saying that $Subject doesn't work, or that the
> > > > above-linked please-review patch doesn't work?
> > >
> > > shmem pays no attention to the mapping_large_folio_support() flag,
> > > so the proposed fix doesn't work. It ought to, but it has its own way
> > > of doing it that predates mapping_large_folio_support existing.
> >
> > Yep. It turned out to be easier to fix xfile.c to deal with large
> > folios than I thought it would be. Or so I think. We'll see what
> > happens on fstestscloud overnight.
>
> Where do we stand with this? Should I merge these two patches into
> 6.8-rcX, cc:stable?

This patchset doesn't actually fix the problem, so no, let's not merge
it.

For 6.9 we'll make xfile.c clean w.r.t. large folios:
https://lore.kernel.org/linux-xfs/20240129143502.189370-1-hch@lst.de/

I don't think we need a 6.8 backport since xfile.c is only used by an
experimental feature that is default n in kconfig.

--D