On 2025/7/14 08:32, 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.
Signed-off-by: Nico Pache <npache@xxxxxxxxxx>
---
mm/khugepaged.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index a701d9f0f158..7a9c4edf0e23 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1367,6 +1367,23 @@ static int collapse_scan_bitmap(struct mm_struct *mm, unsigned long address,
collapsed += (1 << order);
continue;
}
After doing more testing, I think you need to add the following changes
after patch 8.
Because when collapsing mTHP, if we encounter a PTE-mapped large folio
within the PMD range, we should continue scanning to complete that PMD,
in case there is another mTHP that can be collapsed within that PMD range.
+ if (ret == SCAN_PTE_MAPPED_HUGEPAGE)
+ 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
Nit: the 'else' statement can be dropped.
+ break;
}
next:
