diff --git a/sys/vm/vm_object.h b/sys/vm/vm_object.h
--- a/sys/vm/vm_object.h
+++ b/sys/vm/vm_object.h
@@ -198,7 +198,9 @@
 #define	OBJ_COLLAPSING	0x00000800	/* Parent of collapse. */
 #define	OBJ_COLORED	0x00001000	/* pg_color is defined */
 #define	OBJ_ONEMAPPING	0x00002000	/* One USE (a single, non-forked)
-					   mapping flag */
+					   mapping flag.  Each page is allowed
+					   to have at most one mapping.
+					*/
 #define	OBJ_PAGERPRIV1	0x00004000	/* Pager private */
 #define	OBJ_PAGERPRIV2	0x00008000	/* Pager private */
 #define	OBJ_SYSVSHM	0x00010000	/* SysV SHM */