diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index f792940..2f5cf10 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -176,7 +176,8 @@
  * associated range, and a copy of the original mm_walk for access to
  * the ->private or ->mm fields.
  *
- * No locks are taken, but the bottom level iterator will map PTE
+ * Usually no locks are taken, but splitting transparent huge page may
+ * take page table lock. And the bottom level iterator will map PTE
  * directories from highmem if necessary.
  *
  * If any callback returns a non-zero value, the walk is aborted and