re #13613 rb4516 Tunables needs volatile keyword

@@ -23,10 +23,13 @@
  * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
  * Use is subject to license terms.
  * Copyright 2016 Nexenta Systems, Inc.
  * Copyright (c) 2017 by Delphix. All rights reserved.
  */
+/*
+ * Copyright 2013 Nexenta Systems, Inc.  All rights reserved.
+ */
 
 /*      Copyright (c) 1983, 1984, 1985, 1986, 1987, 1988, 1989 AT&T     */
 /*        All Rights Reserved   */
 
 /*

@@ -812,11 +815,10 @@
         struct vnode *rvp = NULL;
         int flags = 0;
         kmutex_t *ihm;
         int elapsed;
         int status;
-        extern  int     maxphys;
 
         if (args_len == sizeof (struct ufs_args) && raw_argsp)
                 flags = ((struct ufs_args *)raw_argsp)->flags;
 
         ASSERT(vfs_lock_held(vfsp));