linux-kernel - Re: [PATCH v12 mm-new 11/15] khugepaged: introduce collapse_allowable

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Message-ID: <CAA1CXcDG8=89uPcptkRv23JfmczAGp6_KQMQOFhQ6Uivo-33kw@mail.gmail.com>
Date: Fri, 7 Nov 2025 11:01:23 -0700
From: Nico Pache <npache@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
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Subject: Re: [PATCH v12 mm-new 11/15] khugepaged: introduce
 collapse_allowable_orders helper function

On Thu, Nov 6, 2025 at 11:51 AM Lorenzo Stoakes
<lorenzo.stoakes@...cle.com> wrote:
>
> On Wed, Oct 22, 2025 at 12:37:13PM -0600, Nico Pache wrote:
> > Add collapse_allowable_orders() to generalize THP order eligibility. The
> > function determines which THP orders are permitted based on collapse
> > context (khugepaged vs madv_collapse).
> >
> > This consolidates collapse configuration logic and provides a clean
> > interface for future mTHP collapse support where the orders may be
> > different.
> >
> > Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> > Signed-off-by: Nico Pache <npache@...hat.com>
>
> With nits below adddressed, LGTM so:
>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

Thank you!

> > ---
> >  mm/khugepaged.c | 15 ++++++++++++---
> >  1 file changed, 12 insertions(+), 3 deletions(-)
> >
> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > index 0dbbe04c31fe..89a105124790 100644
> > --- a/mm/khugepaged.c
> > +++ b/mm/khugepaged.c
> > @@ -489,7 +489,16 @@ static unsigned int collapse_max_ptes_none(unsigned int order, bool full_scan)
> >       max_ptes_none = min(khugepaged_max_ptes_none, HPAGE_PMD_NR/2 - 1);
> >
> >       return max_ptes_none >> (HPAGE_PMD_ORDER - order);
> > +}
> > +
> > +/* Check what orders are allowed based on the vma and collapse type */
> > +static unsigned long collapse_allowable_orders(struct vm_area_struct *vma,
> > +                     vm_flags_t vm_flags, bool is_khugepaged)
> > +{
> > +     enum tva_type tva_flags = is_khugepaged ? TVA_KHUGEPAGED : TVA_FORCED_COLLAPSE;
> > +     unsigned long orders = BIT(HPAGE_PMD_ORDER);
>
> Nit, but can const-ify.

It becomes a function of is_khugepaged in a later patch.

>
> >
> > +     return thp_vma_allowable_orders(vma, vm_flags, tva_flags, orders);
> >  }
> >
> >  void khugepaged_enter_vma(struct vm_area_struct *vma,
> > @@ -497,7 +506,7 @@ void khugepaged_enter_vma(struct vm_area_struct *vma,
> >  {
> >       if (!mm_flags_test(MMF_VM_HUGEPAGE, vma->vm_mm) &&
> >           hugepage_pmd_enabled()) {
> > -             if (thp_vma_allowable_order(vma, vm_flags, TVA_KHUGEPAGED, PMD_ORDER))
> > +             if (collapse_allowable_orders(vma, vm_flags, true))
>
> If we have a 'mystery meat' boolean parameter can we always use the convention of:
>
> collapse_allowable_orders(vma, vm_flags, /*is_khugepaged=*/true)
>
> Please? Same goes for other invocations obviously.

Sounds good! I'll fix those up.

Thanks,
-- Nico

>
>
> >                       __khugepaged_enter(vma->vm_mm);
> >       }
> >  }
> > @@ -2567,7 +2576,7 @@ static unsigned int collapse_scan_mm_slot(unsigned int pages, int *result,
> >                       progress++;
> >                       break;
> >               }
> > -             if (!thp_vma_allowable_order(vma, vma->vm_flags, TVA_KHUGEPAGED, PMD_ORDER)) {
> > +             if (!collapse_allowable_orders(vma, vma->vm_flags, true)) {
> >  skip:
> >                       progress++;
> >                       continue;
> > @@ -2873,7 +2882,7 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
> >       BUG_ON(vma->vm_start > start);
> >       BUG_ON(vma->vm_end < end);
> >
> > -     if (!thp_vma_allowable_order(vma, vma->vm_flags, TVA_FORCED_COLLAPSE, PMD_ORDER))
> > +     if (!collapse_allowable_orders(vma, vma->vm_flags, false))
> >               return -EINVAL;
> >
> >       cc = kmalloc(sizeof(*cc), GFP_KERNEL);
> > --
> > 2.51.0
> >
>