diff --git a/ChangeLog b/ChangeLog
index f52d41c1c0..c3796f4ae6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Sep 30 17:28:39 2013  Koichi Sasada  <ko1@atdot.net>
+
+	* ext/objspace/object_tracing.c: [DOC] add some nots for 
+	  ObjectSpace::trace_object_allocations.
+
 Mon Sep 30 16:46:58 2013  Koichi Sasada  <ko1@atdot.net>
 
 	* ext/objspace/object_tracing.c: add new 3 methods to control tracing.
diff --git a/ext/objspace/object_tracing.c b/ext/objspace/object_tracing.c
index ffb62fe832..fe39aa16f5 100644
--- a/ext/objspace/object_tracing.c
+++ b/ext/objspace/object_tracing.c
@@ -245,7 +245,10 @@ trace_object_allocations_clear(VALUE self)
  *
  * This example has included the ObjectSpace module to make it easier to read,
  * but you can also use the
- * "<code>ObjectSpace::trace_object_allocations</code>" notation.
+ * "<code>ObjectSpace::trace_object_allocations</code>" notation (recommended).
+ *
+ * Note that this feature introduces huge performance down and huge memory
+ * consumption.
  */
 static VALUE
 trace_object_allocations(VALUE self)