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/20241216165105.56185-11-dev.jain@xxxxxxx/ Acked-by: David Hildenbrand <david@xxxxxxxxxx> Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> Co-developed-by: Dev Jain <dev.jain@xxxxxxx> Signed-off-by: Dev Jain <dev.jain@xxxxxxx> Signed-off-by: Nico Pache <npache@xxxxxxxxxx> --- mm/khugepaged.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 1ad7e00d3fd6..6a4cf7e4a7cc 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -611,6 +611,15 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, folio = page_folio(page); VM_BUG_ON_FOLIO(!folio_test_anon(folio), folio); + /* + * TODO: In some cases of partially-mapped folios, we'd actually + * want to collapse. + */ + if (order != HPAGE_PMD_ORDER && folio_order(folio) >= order) { + result = SCAN_PTE_MAPPED_HUGEPAGE; + goto out; + } + /* See collapse_scan_pmd(). */ if (folio_maybe_mapped_shared(folio)) { ++shared; -- 2.50.1
