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

[Matthew Wilcox]

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 at 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 at kernel.org>
> > > > Signed-off-by: Christoph Hellwig <hch at 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 at 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.