Index: sys/vm/vm_page.c
===================================================================
--- sys/vm/vm_page.c	(revision 224703)
+++ sys/vm/vm_page.c	(working copy)
@@ -477,7 +477,6 @@
 vm_page_flag_set(vm_page_t m, unsigned short bits)
 {
 
-	mtx_assert(&vm_page_queue_mtx, MA_OWNED);
 	/*
 	 * The PG_WRITEABLE flag can only be set if the page is managed and
 	 * VPO_BUSY.  Currently, this flag is only set by pmap_enter().
@@ -485,21 +484,44 @@
 	KASSERT((bits & PG_WRITEABLE) == 0 ||
 	    ((m->flags & (PG_UNMANAGED | PG_FICTITIOUS)) == 0 &&
 	    (m->oflags & VPO_BUSY) != 0), ("PG_WRITEABLE and !VPO_BUSY"));
+
+#if defined(__amd64__) || defined(__i386__) || defined(__ia64__)
+	/*
+	 * On the aforementioned architectures, the page queues lock is not
+	 * required by the following read-modify-write operation, an atomic
+	 * operation suffices.
+	 */
+	atomic_set_short(&m->flags, bits);
+#else
+	vm_page_lock_queues();
 	m->flags |= bits;
+	vm_page_unlock_queues();
+#endif
 } 
 
 void
 vm_page_flag_clear(vm_page_t m, unsigned short bits)
 {
 
-	mtx_assert(&vm_page_queue_mtx, MA_OWNED);
 	/*
 	 * The PG_REFERENCED flag can only be cleared if the object
 	 * containing the page is locked.
 	 */
 	KASSERT((bits & PG_REFERENCED) == 0 || VM_OBJECT_LOCKED(m->object),
 	    ("PG_REFERENCED and !VM_OBJECT_LOCKED"));
+
+#if defined(__amd64__) || defined(__i386__) || defined(__ia64__)
+	/*
+	 * On the aforementioned architectures, the page queues lock is not
+	 * required by the following read-modify-write operation, an atomic
+	 * operation suffices.
+	 */
+	atomic_clear_short(&m->flags, bits);
+#else
+	vm_page_lock_queues();
 	m->flags &= ~bits;
+	vm_page_unlock_queues();
+#endif
 }
 
 void
Index: sys/vm/vm_page.h
===================================================================
--- sys/vm/vm_page.h	(revision 224703)
+++ sys/vm/vm_page.h	(working copy)
@@ -233,9 +233,9 @@
 #define	PG_FREE		0x0002		/* page is free */
 #define PG_WINATCFLS	0x0004		/* flush dirty page on inactive q */
 #define	PG_FICTITIOUS	0x0008		/* physical page doesn't exist (O) */
-#define	PG_WRITEABLE	0x0010		/* page is mapped writeable */
+#define	PG_WRITEABLE	0x0010		/* page is mapped writeable (M) */
 #define	PG_ZERO		0x0040		/* page is zeroed */
-#define PG_REFERENCED	0x0080		/* page has been referenced */
+#define PG_REFERENCED	0x0080		/* page has been referenced (M) */
 #define PG_UNMANAGED	0x0800		/* No PV management for page */
 #define PG_MARKER	0x1000		/* special queue marker page */
 #define	PG_SLAB		0x2000		/* object pointer is actually a slab */