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/
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: David Hildenbrand <david@redhat.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 | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 75e7ebdccc36..d741af15e18c 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -629,6 +629,14 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
goto out;
}
}
+ /*
+ * 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;
+ }
if (folio_test_large(folio)) {
struct folio *f;
--
2.51.0