[PATCH mm-unstable v19 12/14] mm/khugepaged: avoid unnecessary mTHP collapse attempts

[Nico Pache]

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 <ljs@xxxxxxxxxx>
Acked-by: Usama Arif <usama.arif@xxxxxxxxx>
Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
Signed-off-by: Nico Pache <npache@xxxxxxxxxx>
---
 mm/khugepaged.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 430047316f43..7de92b28dd30 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1499,6 +1499,7 @@ static enum scan_result mthp_collapse(struct mm_struct *mm,
 			collapse_address = address + offset * PAGE_SIZE;
 			ret = collapse_huge_page(mm, collapse_address, referenced,
 						 unmapped, cc, order);
+
 			switch (ret) {
 			/* Cases where we continue to next collapse candidate */
 			case SCAN_SUCCEED:
@@ -1509,6 +1510,18 @@ static enum scan_result mthp_collapse(struct mm_struct *mm,
 			/* Cases where lower orders might still succeed */
 			case SCAN_ALLOC_HUGE_PAGE_FAIL:
 				alloc_failed = true;
+				fallthrough;
+			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_PAGE_LAZYFREE:
 				last_result = ret;
 				goto next_order;
 			/* Cases where no further collapse is possible */
-- 
2.54.0