[PATCH v7 09/12] 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.

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

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 5920d4715a11..517cf2b271d7 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1371,6 +1371,23 @@ 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:
-- 
2.49.0