[PATCH v4 09/12] khugepaged: avoid unnecessary mTHP collapse attempts

Nico Pache
2025-04-17T00:07:27Z

There are cases where, if an attempted collapse fails, all subsequent
orders are guaranteed to also fail. Avoid these collapse attempts by
bailing out early.

Signed-off-by: Nico Pache <npache@redhat.com>
---
mm/khugepaged.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 383aff12cd43..738dd9c5751d 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1366,6 +1366,23 @@ static int khugepaged_scan_bitmap(struct mm_struct *mm, unsigned long address,
collapsed += (1 << order);
continue;
}
+ /*
+ * Some ret values indicate all lower order will also
+ * fail, dont trying to collapse smaller orders
+ */
+ if (ret == SCAN_EXCEED_NONE_PTE ||
+ ret == SCAN_EXCEED_SWAP_PTE ||
+ ret == SCAN_EXCEED_SHARED_PTE ||
+ ret == SCAN_PTE_NON_PRESENT ||
+ ret == SCAN_PTE_UFFD_WP ||
+ ret == SCAN_ALLOC_HUGE_PAGE_FAIL ||
+ ret == SCAN_CGROUP_CHARGE_FAIL ||
+ ret == SCAN_COPY_MC ||
+ ret == SCAN_PAGE_LOCK ||
+ ret == SCAN_PAGE_COUNT)
+ goto next;
+ else
+ break;
}

next:
--
2.48.1