On 2026/6/1 04:02, David Hildenbrand (Arm) wrote:
On 5/31/26 09:31, Lance Yang wrote:
On Fri, May 22, 2026 at 09:00:07AM -0600, Nico Pache wrote:
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.
Reviewed-by: Lorenzo Stoakes <[email protected]>
Acked-by: Usama Arif <[email protected]>
Acked-by: David Hildenbrand (Arm) <[email protected]>
Signed-off-by: Nico Pache <[email protected]>
---
mm/khugepaged.c | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index d3d7db8be26c..15b7298bc225 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1535,9 +1535,31 @@ static int mthp_collapse(struct mm_struct *mm, struct
vm_area_struct *vma,
collapse_address = address + offset * PAGE_SIZE;
ret = collapse_huge_page(mm, collapse_address,
referenced,
unmapped, cc, order);
- if (ret == SCAN_SUCCEED) {
+
+ switch (ret) {
+ /* Cases where we continue to next collapse candidate */
+ case SCAN_SUCCEED:
collapsed += nr_ptes;
+ fallthrough;
+ case SCAN_PTE_MAPPED_HUGEPAGE:
continue;
+ /* Cases where 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_NULL:
+ case SCAN_DEL_PAGE_LRU:
+ case SCAN_PTE_NON_PRESENT:
+ case SCAN_PTE_UFFD_WP:
+ case SCAN_ALLOC_HUGE_PAGE_FAIL:
Nit: shouldn't SCAN_CGROUP_CHARGE_FAIL go with SCAN_ALLOC_HUGE_PAGE_FAIL
here?
If charging the current order fails, a smaller order might still fit :)
I think the reasoning was here, that if we are already that close to our mem
limit, we should just give up instead of trying to squeeze it in .. :)
Fair point. Just a nit, nevermind :)
