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

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Message-ID: <20250417000238.74567-10-npache@redhat.com>
Date: Wed, 16 Apr 2025 18:02:35 -0600
From: Nico Pache <npache@...hat.com>
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Subject: [PATCH v4 09/12] khugepaged: avoid unnecessary mTHP collapse attempts

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@...hat.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