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

[Baolin Wang]

On 4/7/26 2:49 PM, Lance Yang wrote:
> On Tue, Apr 07, 2026 at 02:07:27PM +0800, Baolin Wang wrote:
> > Anonymous shmem large order allocations are dynamically controlled via the
> > global THP sysfs knob (/sys/kernel/mm/transparent_hugepage/shmem_enabled)
> > and the per-size mTHP knobs (/sys/kernel/mm/transparent_hugepage/hugepages-<size>kB/shmem_enabled).
> >
> > Therefore, anonymous shmem uses shmem_allowable_huge_orders() to check
> > which large orders are allowed, rather than relying on mapping_max_folio_order().
> > Moreover, mapping_max_folio_order() is intended to control large order
> > allocations only for tmpfs mounts. Clarify this by not setting a large-order
> > range for internal anonymous shmem mappings, to avoid confusion, as discussed
> > in the previous thread[1].
> >
> > [1] https://lore.kernel.org/all/ec927492-4577-4192-8fad-85eb1bb43121@xxxxxxxxxxxxxxxxx/
> > Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> > ---
> > mm/shmem.c | 13 +++++++++++--
> > 1 file changed, 11 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/shmem.c b/mm/shmem.c
> > index 4ecefe02881d..a60fe067969c 100644
> > --- a/mm/shmem.c
> > +++ b/mm/shmem.c
> > @@ -3088,8 +3088,17 @@ static struct inode *__shmem_get_inode(struct mnt_idmap *idmap,
> > 	if (sbinfo->noswap)
> > 		mapping_set_unevictable(inode->i_mapping);
> >
> > -	/* Don't consider 'deny' for emergencies and 'force' for testing */
> > -	if (sbinfo->huge)
> > +	/*
> > +	 * Only set the large order range for tmpfs mounts. The large order
> > +	 * selection for the internal anonymous shmem mount is configured
> > +	 * dynamically via the 'shmem_enabled' interfaces, so there is no
> > +	 * need to set a large order range for the internal anonymous shmem
> > +	 * mapping.
> > +	 *
> > +	 * Note: Don't consider 'deny' for emergencies and 'force' for
> > +	 * testing.
> > +	 */
> > +	if (sbinfo->huge && !(sb->s_flags & SB_KERNMOUNT))
>
> FWIW, SB_KERNMOUNT is broader than "internal anonymous shmem" and covers
> all shm_mnt users too.
>
> So maybe "internal shmem mount" would be a better description of what
> this code is actually checking.

Right, good point. Will fix. Thanks.