linux-kernel - Re: [PATCH v13 mm-new 05/16] khugepaged: introduce is_mthp

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Message-ID: <CAA1CXcC9YsOKbsvyZpgOwLdE938VBcPUrLyF97uN024uM2uiPA@mail.gmail.com>
Date: Tue, 13 Jan 2026 19:38:39 -0700
From: Nico Pache <npache@...hat.com>
To: Zi Yan <ziy@...dia.com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	linux-mm@...ck.org, linux-doc@...r.kernel.org, david@...hat.com, 
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Subject: Re: [PATCH v13 mm-new 05/16] khugepaged: introduce is_mthp_order helper

On Tue, Dec 2, 2025 at 8:13 PM Zi Yan <ziy@...dia.com> wrote:
>
> On 1 Dec 2025, at 12:46, Nico Pache wrote:
>
> > In order to add mTHP support, we will often be checking if a given order
> > is a mTHP or PMD order. Lets create a simple helper function to keep the
> > code clean and readable.
> >
> > Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> > Signed-off-by: Nico Pache <npache@...hat.com>
> > ---
> >  mm/khugepaged.c | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > index 8599c7fa112e..9c041141b2e3 100644
> > --- a/mm/khugepaged.c
> > +++ b/mm/khugepaged.c
> > @@ -338,6 +338,11 @@ static bool pte_none_or_zero(pte_t pte)
> >       return pte_present(pte) && is_zero_pfn(pte_pfn(pte));
> >  }
> >
> > +static bool is_mthp_order(unsigned int order)
> > +{
> > +     return order != HPAGE_PMD_ORDER;
> > +}
> > +
>
> The code at the bottom of __folio_split() in mm/huge_memory.c
> can use this helper.
>
> The code in deferred_split_folio() uses folio_test_pmd_mappable()
> instead of order == HPAGE_PMD_ORDER, but the code can be changed
> to use the helper.

static inline bool folio_test_pmd_mappable(struct folio *folio)
{
return folio_order(folio) >= HPAGE_PMD_ORDER;
}

Should we make the is_mthp_order() check all orders that are less than
HPAGE_PMD_ORDER.

ie)

+static bool is_mthp_order(unsigned int order)
+{
+     return order < HPAGE_PMD_ORDER;
}

This way it's true to its mTHP nature being smaller than the PMD.

Cheers,
-- Nico

>
> >  int hugepage_madvise(struct vm_area_struct *vma,
> >                    vm_flags_t *vm_flags, int advice)
> >  {
> > @@ -1071,13 +1076,13 @@ static int alloc_charge_folio(struct folio **foliop, struct mm_struct *mm,
> >       folio = __folio_alloc(gfp, order, node, &cc->alloc_nmask);
> >       if (!folio) {
> >               *foliop = NULL;
> > -             if (order == HPAGE_PMD_ORDER)
> > +             if (!is_mthp_order(order))
> >                       count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
> >               count_mthp_stat(order, MTHP_STAT_COLLAPSE_ALLOC_FAILED);
> >               return SCAN_ALLOC_HUGE_PAGE_FAIL;
> >       }
> >
> > -     if (order == HPAGE_PMD_ORDER)
> > +     if (!is_mthp_order(order))
> >               count_vm_event(THP_COLLAPSE_ALLOC);
> >       count_mthp_stat(order, MTHP_STAT_COLLAPSE_ALLOC);
> >
> > --
> > 2.51.1
>
>
> Best Regards,
> Yan, Zi
>