On 14.07.25 02:32, 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/20241216165105.56185-11-dev.jain@xxxxxxx/
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 | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 5d7c5be9097e..a701d9f0f158 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -612,7 +612,12 @@ 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;
+ }
Probably worth adding a TODO in the code like
/*
* TODO: In some cases of partially-mapped folios, we'd actually
* want to collapse.
*/
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
--
Cheers,
David / dhildenb
