[PATCH mm-unstable v18 12/14] mm/khugepaged: avoid unnecessary mTHP collapse attempts
From: Nico Pache <hidden>
Date: 2026-05-22 15:03:50
Also in:
linux-doc, linux-mm, lkml
Subsystem:
memory management, memory management - thp (transparent huge page), the rest · Maintainers:
Andrew Morton, David Hildenbrand, Linus Torvalds
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@kernel.org> Acked-by: Usama Arif <usama.arif@linux.dev> Acked-by: David Hildenbrand (Arm) <david@kernel.org> Signed-off-by: Nico Pache <redacted> --- 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: + case SCAN_PAGE_LAZYFREE: + goto next_order; + /* Cases where no further collapse is possible */ + default: + return collapsed; } }
--
2.54.0