Re: [PATCH v10 03/13] khugepaged: generalize hugepage_vma_revalidate for mTHP support

[Nico Pache <npache@redhat.com>]

On Wed, Aug 20, 2025 at 7:25 AM Lorenzo Stoakes
<lorenzo.stoakes@oracle.com> wrote:
>
> On Tue, Aug 19, 2025 at 07:41:55AM -0600, Nico Pache wrote:
> > For khugepaged to support different mTHP orders, we must generalize this
> > to check if the PMD is not shared by another VMA and the order is enabled.
> >
> > To ensure madvise_collapse can support working on mTHP orders without the
> > PMD order enabled, we need to convert hugepage_vma_revalidate to take a
> > bitmap of orders.
> >
> > No functional change in this patch.
> >
> > Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> > Acked-by: David Hildenbrand <david@redhat.com>
> > Co-developed-by: Dev Jain <dev.jain@arm.com>
> > Signed-off-by: Dev Jain <dev.jain@arm.com>
> > Signed-off-by: Nico Pache <npache@redhat.com>
>
> LGTM (modulo nit/query below) so:
>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Thanks :)
>
> > ---
> >  mm/khugepaged.c | 13 ++++++++-----
> >  1 file changed, 8 insertions(+), 5 deletions(-)
> >
> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > index b7b98aebb670..2d192ec961d2 100644
> > --- a/mm/khugepaged.c
> > +++ b/mm/khugepaged.c
> > @@ -917,7 +917,7 @@ static int collapse_find_target_node(struct collapse_control *cc)
> >  static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
> >                                  bool expect_anon,
> >                                  struct vm_area_struct **vmap,
> > -                                struct collapse_control *cc)
> > +                                struct collapse_control *cc, unsigned long orders)
> >  {
> >       struct vm_area_struct *vma;
> >       enum tva_type type = cc->is_khugepaged ? TVA_KHUGEPAGED :
> > @@ -930,9 +930,10 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
> >       if (!vma)
> >               return SCAN_VMA_NULL;
> >
> > +     /* Always check the PMD order to insure its not shared by another VMA */
>
> NIT: ensure not insure.
ack, ill fix that!
>
> >       if (!thp_vma_suitable_order(vma, address, PMD_ORDER))
> >               return SCAN_ADDRESS_RANGE;
> > -     if (!thp_vma_allowable_order(vma, vma->vm_flags, type, PMD_ORDER))
> > +     if (!thp_vma_allowable_orders(vma, vma->vm_flags, type, orders))
> >               return SCAN_VMA_CHECK;
> >       /*
> >        * Anon VMA expected, the address may be unmapped then
> > @@ -1134,7 +1135,8 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
> >               goto out_nolock;
> >
> >       mmap_read_lock(mm);
> > -     result = hugepage_vma_revalidate(mm, address, true, &vma, cc);
> > +     result = hugepage_vma_revalidate(mm, address, true, &vma, cc,
> > +                                      BIT(HPAGE_PMD_ORDER));
>
> Shouldn't this be PMD order? Seems equivalent.
Yeah i'm actually not sure why we have both... they seem to be the
same thing, but perhaps there is some reason for having two...
>
> >       if (result != SCAN_SUCCEED) {
> >               mmap_read_unlock(mm);
> >               goto out_nolock;
> > @@ -1168,7 +1170,8 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
> >        * mmap_lock.
> >        */
> >       mmap_write_lock(mm);
> > -     result = hugepage_vma_revalidate(mm, address, true, &vma, cc);
> > +     result = hugepage_vma_revalidate(mm, address, true, &vma, cc,
> > +                                      BIT(HPAGE_PMD_ORDER));
> >       if (result != SCAN_SUCCEED)
> >               goto out_up_write;
> >       /* check if the pmd is still valid */
> > @@ -2807,7 +2810,7 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
> >                       mmap_read_lock(mm);
> >                       mmap_locked = true;
> >                       result = hugepage_vma_revalidate(mm, addr, false, &vma,
> > -                                                      cc);
> > +                                                      cc, BIT(HPAGE_PMD_ORDER));
> >                       if (result  != SCAN_SUCCEED) {
> >                               last_fail = result;
> >                               goto out_nolock;
> > --
> > 2.50.1
> >
>