Re: [PATCH v2 07/10] mm/shmem_luo: Retrieve tmpfs files onto a tmpfs mount chosen by userspace

[David Matlack]

On 2026-10-28 06:02 PM, Pasha Tatashin wrote:

> > +/*
> > + * Whether @inode is on the internal shmem mount, which is used by
> > + * shmem_file_setup() and thus by memfd_create().
> > + */
> > +bool shmem_inode_on_internal_mount(const struct inode *inode)
> > +{
> > +	return inode->i_sb == shm_mnt->mnt_sb;
> > +}
> 
> Please fix the warning reported by kernel test robot.

Will do.

The prototype for shmem_inode_on_internal_mount() is in mm/internal.h,
which mm/shmem.c only includes if CONFIG_SHMEM=y, but the robot was
building without CONFIG_SHMEM. I've moved the definition of this
function into CONFIG_SHMEM in v3 to fix this.

> Looking at this together with Pratyush's mapping-freeze series ([PATCH
> 0/3] mm: allow freezing mappings), I think we should extend the mapping
> freeze lifecycle from preserve() -> retrieve() to preserve() ->
> finish().
>
> When retrieve() returns an fd, its mapping should still come out frozen
> and only become fully user-owned/mutable once a successful session
> finish() happens. That keeps the index -> folio mapping invariant across
> the entire live update until every fd in the session (e.g. vmfd,
> iommufd, vfiofd that depend on the memfd) has been retrieved, passed
> can_finish(), and been finalized together in finish().
>
> (Doesn't have to block this series, we can do it on top or as part of
> Pratyush's AS_FROZEN series.), but I think we must fix it either here or
> there.)

Ok that sounds reasonable. Should we do that as part of Pratyush's
series then?

Pratyuh's series replaces shmem_freeze() with mapping_set_frozen(), so
retrieve() would freeze the new file and finish() would unfreeze it.
That should work the same for memfds and tmpfs files..

BTW, this tmpfs series does a lot of renames and code motion so it
conflicts with Pratyush's series. How should we order these?