On Tue, Dec 2, 2025 at 8:13 PM Zi Yan [off-list ref] wrote:

On 1 Dec 2025, at 12:46, Nico Pache wrote:

quoted

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 <redacted>
Signed-off-by: Nico Pache <npache@redhat.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

quoted

 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