Re: [PATCH v2] mm: shmem: don't set large-order range for internal shmem mount

[Baolin Wang]

On 4/15/26 10:36 PM, David Hildenbrand (Arm) wrote:
> On 4/15/26 12:05, Baolin Wang wrote:
> > On 4/15/26 5:54 PM, David Hildenbrand (Arm) wrote:
> > > > Yes, that makes sense.
> > > >
> > > > However, it’s also possible that the mapping does not support large
> > > > folios, yet anonymous shmem can still allocate large folios via the
> > > > sysfs interfaces. That doesn't make sense, right?
> > >
> > > That's what I am saying: if there could be large folios in there, then
> > > let's tell the world.
> > >
> > > Getting in a scenario where the mapping claims to not support large
> > > folios, but then we have large folios in there is inconsistent, not?
> > >
> > > [...]
> > >
> > > > For the current anonymous shmem (tmpfs is already clear, no questions),
> > > > I don’t think there will be any "will never have/does never allow"
> > > > cases, because it can be changed dynamically via the sysfs interfaces.
> > >
> > > Right. It's about non-anon shmem with huge=off.
> > >
> > > > If we still want that logic, then for anonymous shmem we can treat it as
> > > > always "might have large folios".
> >
> > OK. To resolve the confusion about 1, the logic should be changed as
> > follows. Does that make sense to you?
> >
> > if (sbinfo->huge || (sb->s_flags & SB_KERNMOUNT))
> >      mapping_set_large_folios(inode->i_mapping);
>
> I think that's better.

Thanks for your valuable input.

But has Willy says, maybe we can just
> unconditionally set it and have it even simpler.

However, for tmpfs mounts, we should still respect the 'huge=' mount 
option. See commit 5a90c155defa ("tmpfs: don't enable large folios if 
not supported").