Index: sys/vm/uma_core.c
===================================================================
--- sys/vm/uma_core.c
+++ sys/vm/uma_core.c
@@ -1568,7 +1568,14 @@
 		    "new wasted space = %d\n", keg->uk_name, keg, wastedspace,
 		    slabsize / UMA_MAX_WASTE, keg->uk_ipers,
 		    slabsize - keg->uk_ipers * keg->uk_rsize);
-		keg->uk_flags |= UMA_ZONE_OFFPAGE;
+		/*
+		 * If we had access to memory to embed a slab header we
+		 * also have a page structure to use vtoslab() instead of
+		 * hash to find slabs.  If the zone was explicitly created
+		 * OFFPAGE we can't necessarily touch the memory.
+		 */
+		if ((keg->uk_flags & UMA_ZONE_OFFPAGE) == 0)
+			keg->uk_flags |= UMA_ZONE_OFFPAGE | UMA_ZONE_VTOSLAB;
 	}
 
 	if ((keg->uk_flags & UMA_ZONE_OFFPAGE) &&
@@ -1608,7 +1615,7 @@
 		 * slab header.
 		 */
 		if ((keg->uk_flags & UMA_ZFLAG_INTERNAL) == 0)
-			keg->uk_flags |= UMA_ZONE_OFFPAGE;
+			keg->uk_flags |= UMA_ZONE_OFFPAGE | UMA_ZONE_VTOSLAB;
 		else
 			keg->uk_ppera++;
 	}