On Thu, Apr 24, 2025 at 1:49 AM Baolin Wang <[email protected]> wrote: > > > > On 2025/4/17 08:02, Nico Pache wrote: > > khugepaged may try to collapse a mTHP to a smaller mTHP, resulting in > > some pages being unmapped. Skip these cases until we have a way to check > > if its ok to collapse to a smaller mTHP size (like in the case of a > > partially mapped folio). > > > > This patch is inspired by Dev Jain's work on khugepaged mTHP support [1]. > > > > [1] https://lore.kernel.org/lkml/[email protected]/ > > > > Co-developed-by: Dev Jain <[email protected]> > > Signed-off-by: Dev Jain <[email protected]> > > Signed-off-by: Nico Pache <[email protected]> > > --- > > mm/khugepaged.c | 7 ++++++- > > 1 file changed, 6 insertions(+), 1 deletion(-) > > > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > index ece39fd71fe6..383aff12cd43 100644 > > --- a/mm/khugepaged.c > > +++ b/mm/khugepaged.c > > @@ -625,7 +625,12 @@ static int __collapse_huge_page_isolate(struct > > vm_area_struct *vma, > > folio = page_folio(page); > > VM_BUG_ON_FOLIO(!folio_test_anon(folio), folio); > > > > - /* See hpage_collapse_scan_pmd(). */ > > + if (order != HPAGE_PMD_ORDER && folio_order(folio) >= order) { > > + result = SCAN_PTE_MAPPED_HUGEPAGE; > > + goto out; > > + } > > Should we also add this check in hpage_collapse_scan_pmd() to abort the > scan early? No I dont think so, we can't abort there because we dont know the attempted collapse order, and we dont want to miss potential mTHP collapses (by bailing out early and not populating the bitmap).
-- Nico >
