[PATCH mm-unstable v15 11/13] mm/khugepaged: avoid unnecessary mTHP collapse attempts

Nico Pache
2026-02-26T03:26:54Z

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 | 35 ++++++++++++++++++++++++++++++++++-
1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 1c3711ed4513..388d3f2537e2 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1492,9 +1492,42 @@ static int mthp_collapse(struct mm_struct *mm, unsigned long address,
ret = collapse_huge_page(mm, collapse_address, referenced,
unmapped, cc, mmap_locked,
order);
- if (ret == SCAN_SUCCEED) {
+
+ switch (ret) {
+ /* Cases were we continue to next collapse candidate */
+ case SCAN_SUCCEED:
collapsed += nr_pte_entries;
+ fallthrough;
+ case SCAN_PTE_MAPPED_HUGEPAGE:
continue;
+ /* Cases were lower orders might still succeed */
+ case SCAN_LACK_REFERENCED_PAGE:
+ case SCAN_EXCEED_NONE_PTE:
+ case SCAN_EXCEED_SWAP_PTE:
+ case SCAN_EXCEED_SHARED_PTE:
+ case SCAN_PAGE_LOCK:
+ case SCAN_PAGE_COUNT:
+ case SCAN_PAGE_LRU:
+ case SCAN_PAGE_NULL:
+ case SCAN_DEL_PAGE_LRU:
+ case SCAN_PTE_NON_PRESENT:
+ case SCAN_PTE_UFFD_WP:
+ case SCAN_ALLOC_HUGE_PAGE_FAIL:
+ goto next_order;
+ /* Cases were no further collapse is possible */
+ case SCAN_CGROUP_CHARGE_FAIL:
+ case SCAN_COPY_MC:
+ case SCAN_ADDRESS_RANGE:
+ case SCAN_NO_PTE_TABLE:
+ case SCAN_ANY_PROCESS:
+ case SCAN_VMA_NULL:
+ case SCAN_VMA_CHECK:
+ case SCAN_SCAN_ABORT:
+ case SCAN_PAGE_ANON:
+ case SCAN_PMD_MAPPED:
+ case SCAN_FAIL:
+ default:
+ return collapsed;
}
}

--
2.53.0