Re: [PATCH v12 mm-new 11/15] khugepaged: introduce collapse_allowable_orders helper function

Nico Pache
2025-11-07T18:02:02Z

On Thu, Nov 6, 2025 at 11:51 AM Lorenzo Stoakes
<lorenzo.stoakes@oracle.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@linux.alibaba.com>
> > Signed-off-by: Nico Pache <npache@redhat.com>
>
> With nits below adddressed, LGTM so:
>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.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
> >
>