On 13 Jan 2026, at 21:38, Nico Pache wrote: > On Tue, Dec 2, 2025 at 8:13 PM Zi Yan <[email protected]> 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 <[email protected]> >>> Signed-off-by: Nico Pache <[email protected]> >>> --- >>> 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.
I am not sure. It really depends on in the future whether we call > 9 order (can be mapped by multiple PMDs) large folio mTHP or not. My current feeling is that THP is a legacy name for PMD THP and any other large folios are mTHP. So your current definition of is_mthp_order() looks right to me. This is just my feeling and I am open to other opinions. folio_test_pmd_mappable() is different, since as long as a folio's order is greater than HPAGE_PMD_ORDER, it indeed can be mapped by PMDs. -- Best Regards, Yan, Zi
