From: Lance Yang The existing check in hpage_collapse_scan_pmd() is specific to uffd-wp markers. Other special markers (e.g., GUARD, POISONED) would not be caught early, leading to failures deeper in the swap-in logic. hpage_collapse_scan_pmd() `- collapse_huge_page() `- __collapse_huge_page_swapin() -> fails! As David suggested[1], this patch skips any such non-swap entries early. If a special marker is found, the scan is aborted immediately with the SCAN_PTE_NON_PRESENT result, as Lorenzo suggested[2], avoiding wasted work. [1] https://lore.kernel.org/linux-mm/7840f68e-7580-42cb-a7c8-1ba64fd6df69@redhat.com [2] https://lore.kernel.org/linux-mm/7df49fe7-c6b7-426a-8680-dcd55219c8bd@lucifer.local Suggested-by: David Hildenbrand Suggested-by: Lorenzo Stoakes Signed-off-by: Lance Yang --- mm/khugepaged.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 7ab2d1a42df3..e9778e7734b5 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1285,16 +1285,19 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm, _pte++, addr += PAGE_SIZE) { pte_t pteval = ptep_get(_pte); if (is_swap_pte(pteval)) { + swp_entry_t swp = pte_to_swp_entry(pteval); ++unmapped; if (!cc->is_khugepaged || unmapped <= khugepaged_max_ptes_swap) { /* - * Always be strict with uffd-wp - * enabled swap entries. Please see - * comment below for pte_uffd_wp(). + * Always be strict with PTE markers, which are + * special non-swap entries (e.g., for UFFD_WP, + * POISONED, GUARD). We cannot collapse over + * them, so just abort the scan here. */ - if (pte_swp_uffd_wp_any(pteval)) { - result = SCAN_PTE_UFFD_WP; + if (is_pte_marker_entry(swp) && + pte_marker_get(swp)) { + result = SCAN_PTE_NON_PRESENT; goto out_unmap; } continue; -- 2.49.0