Re: [PATCH v5 07/14] mm: shmem: allow THP support determination at folio allocation time

[Baolin Wang]

On 6/1/26 8:20 PM, Luiz Capitulino wrote:
> On 2026-06-01 08:09, Baolin Wang wrote:
> > On 5/29/26 10:55 PM, Luiz Capitulino wrote:
> > > In order to enable THP support in shmem today, besides the user
> > > configuration required, the CPU must support PMD-sized pages. This
> > > is the case because of the following has_transparent_hugepage()
> > > usage:
> > >
> > > - shmem_parse_one() and shmem_parse_huge(): Check if THP is built-in and
> > >    if the CPU supports PMD-sized pages
> > >
> > > - shmem_init(): Since the CONFIG_TRANSPARENT_HUGEPAGE guard is outside
> > >    the code block calling has_transparent_hugepage(), the
> > >    has_transparent_hugepage() call is exclusively checking if the CPU
> > >    supports PMD-sized pages
> > >
> > > While it's necessary to check if CONFIG_TRANSPARENT_HUGEPAGE is enabled
> > > in all cases, shmem can determine THP size support at folio allocation
> > > time. Therefore, drop the has_transparent_hugepage() usage listed above
> > > while keeping the CONFIG_TRANSPARENT_HUGEPAGE checks.
> > >
> > > Additionally, we need to check if PMD size order is supported in
> > > shmem_getattr(). Use pgtable_has_pmd_leaves() for that.
> > >
> > > Signed-off-by: Luiz Capitulino <luizcap@xxxxxxxxxx>
> > > ---
> > >   mm/shmem.c | 9 +++++----
> > >   1 file changed, 5 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/mm/shmem.c b/mm/shmem.c
> > > index 88bc0c292f1a..108dc969b92a 100644
> > > --- a/mm/shmem.c
> > > +++ b/mm/shmem.c
> > > @@ -689,7 +689,7 @@ static int shmem_parse_huge(const char *str)
> > >       else
> > >           return -EINVAL;
> > > -    if (!has_transparent_hugepage() &&
> > > +    if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
> > >           huge != SHMEM_HUGE_NEVER && huge != SHMEM_HUGE_DENY)
> > >           return -EINVAL;
> > > @@ -1303,6 +1303,8 @@ static int shmem_getattr(struct mnt_idmap *idmap,
> > >       generic_fillattr(idmap, request_mask, inode, stat);
> > >       orders = shmem_huge_global_enabled(inode, 0, 0, false, NULL, 0);
> > > +    if (!pgtable_has_pmd_leaves())
> > > +        orders &= ~BIT(PMD_ORDER);
> >
> > Ah, you did in this patch, but this change should belong in patch 14?
>
> If we move it, then this patch will add a temporary issue until patch 14
> where shmem_getattr() may report PMD-size for blksize even when the CPU
> doesn't support PMD-sized pages.

OK. I see. Feel free to add:

Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>