[PATCH v6 08/12] khugepaged: skip collapsing mTHP to smaller orders
From: Nico Pache <npache@redhat.com>
Date: 2025-05-15 03:05:52
Also in:
linux-doc, linux-mm, lkml
Subsystem:
memory management, memory management - thp (transparent huge page), the rest · Maintainers:
Andrew Morton, David Hildenbrand, Lorenzo Stoakes, Linus Torvalds
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@arm.com/ (local) Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com> Co-developed-by: Dev Jain <dev.jain@arm.com> Signed-off-by: Dev Jain <dev.jain@arm.com> Signed-off-by: Nico Pache <npache@redhat.com> --- mm/khugepaged.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index afad75fc01b7..5920d4715a11 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; + } + + /* See khugepaged_scan_pmd(). */ if (folio_maybe_mapped_shared(folio)) { ++shared; if (order != HPAGE_PMD_ORDER || (cc->is_khugepaged &&
--
2.49.0