Index: sys/security/mac/mac_process.c
===================================================================
--- sys/security/mac/mac_process.c
+++ sys/security/mac/mac_process.c
@@ -252,7 +252,7 @@
 mac_proc_vm_revoke_recurse(struct thread *td, struct ucred *cred,
     struct vm_map *map)
 {
-	vm_map_entry_t vme;
+	vm_map_entry_t prev, vme;
 	int result;
 	vm_prot_t revokeperms;
 	vm_object_t backing_object, object;
@@ -264,7 +264,8 @@
 		return;
 
 	vm_map_lock(map);
-	for (vme = map->header.next; vme != &map->header; vme = vme->next) {
+	for (prev = &map->header;
+	    (vme = prev->next) != &map->header; prev = vme) {
 		if (vme->eflags & MAP_ENTRY_IS_SUB_MAP) {
 			mac_proc_vm_revoke_recurse(td, cred,
 			    vme->object.sub_map);
@@ -363,7 +364,7 @@
 			}
 			pmap_protect(map->pmap, vme->start, vme->end,
 			    vme->protection & ~revokeperms);
-			vm_map_simplify_entry(map, vme);
+			vm_map_try_merge_entries(map, prev, vme);
 		}
 	}
 	vm_map_unlock(map);
Index: sys/vm/vm_map.h
===================================================================
--- sys/vm/vm_map.h
+++ sys/vm/vm_map.h
@@ -418,7 +418,8 @@
 boolean_t vm_map_lookup_entry (vm_map_t, vm_offset_t, vm_map_entry_t *);
 int vm_map_protect (vm_map_t, vm_offset_t, vm_offset_t, vm_prot_t, boolean_t);
 int vm_map_remove (vm_map_t, vm_offset_t, vm_offset_t);
-void vm_map_simplify_entry(vm_map_t map, vm_map_entry_t entry);
+void vm_map_try_merge_entries(vm_map_t map, vm_map_entry_t prev,
+    vm_map_entry_t entry);
 void vm_map_startup (void);
 int vm_map_submap (vm_map_t, vm_offset_t, vm_offset_t, vm_map_t);
 int vm_map_sync(vm_map_t, vm_offset_t, vm_offset_t, boolean_t, boolean_t);
Index: sys/vm/vm_map.c
===================================================================
--- sys/vm/vm_map.c
+++ sys/vm/vm_map.c
@@ -1546,7 +1546,7 @@
 				map->size += end - prev_entry->end;
 			vm_map_entry_resize(map, prev_entry,
 			    end - prev_entry->end);
-			vm_map_simplify_entry(map, prev_entry);
+			vm_map_try_merge_entries(map, prev_entry, prev_entry->next);
 			return (KERN_SUCCESS);
 		}
 
@@ -1606,7 +1606,8 @@
 	 * with the previous entry when object is NULL.  Here, we handle the
 	 * other cases, which are less common.
 	 */
-	vm_map_simplify_entry(map, new_entry);
+	vm_map_try_merge_entries(map, prev_entry, new_entry);
+	vm_map_try_merge_entries(map, new_entry, new_entry->next);
 
 	if ((cow & (MAP_PREFAULT | MAP_PREFAULT_PARTIAL)) != 0) {
 		vm_map_pmap_enter(map, start, prot, object, OFF_TO_IDX(offset),
@@ -2075,6 +2076,26 @@
 }
 
 /*
+ *	vm_map_try_merge_entries:
+ *
+ *	Compare the given map entry to its predecessor, and merge it into its
+ *	predecessor if possible.  The entry remains valid, and may be extended.
+ *	The predecessor may be deleted.
+ *
+ *	The map must be locked.
+ */
+void
+vm_map_try_merge_entries(vm_map_t map, vm_map_entry_t prev, vm_map_entry_t entry)
+{
+
+	if ((entry->eflags & MAP_ENTRY_NOMERGE_MASK) == 0 &&
+	    vm_map_mergeable_neighbors(prev, entry)) {
+		vm_map_entry_unlink(map, prev, UNLINK_MERGE_NEXT);
+		vm_map_merged_neighbor_dispose(map, prev);
+	}
+}
+
+/*
  *	vm_map_simplify_entry:
  *
  *	Simplify the given map entry by merging with either neighbor.  This
@@ -2086,7 +2107,7 @@
  *	possibly extended).  When merging, this routine may delete one or
  *	both neighbors.
  */
-void
+static void
 vm_map_simplify_entry(vm_map_t map, vm_map_entry_t entry)
 {
 	vm_map_entry_t next, prev;
@@ -2176,7 +2197,7 @@
  *	This routine is called only when it is known that
  *	the entry must be split.
  */
-static void
+static vm_map_entry_t
 _vm_map_clip_start(vm_map_t map, vm_map_entry_t entry, vm_offset_t start)
 {
 	vm_map_entry_t new_entry;
@@ -2218,6 +2239,7 @@
 		 * left the same.
 		 */
 	}
+	return (new_entry);
 }
 
 /*
@@ -2447,7 +2469,7 @@
 vm_map_protect(vm_map_t map, vm_offset_t start, vm_offset_t end,
 	       vm_prot_t new_prot, boolean_t set_max)
 {
-	vm_map_entry_t current, entry, in_tran;
+	vm_map_entry_t current, entry, in_tran, prev;
 	vm_object_t obj;
 	struct ucred *cred;
 	vm_prot_t old_prot;
@@ -2470,8 +2492,11 @@
 
 	VM_MAP_RANGE_CHECK(map, start, end);
 
-	if (!vm_map_lookup_entry(map, start, &entry))
-		entry = entry->next;
+	if (start == 0)
+		prev = &map->header;
+	else
+		vm_map_lookup_entry(map, start - 1, &prev);
+	entry = (prev->end > start) ? prev : prev->next;
 
 	/*
 	 * Make a first pass to check for protection violations.
@@ -2513,7 +2538,8 @@
 	 * some may now be mergeable.
 	 */
 	rv = KERN_SUCCESS;
-	vm_map_clip_start(map, entry, start);
+	if (prev == entry)
+		prev = _vm_map_clip_start(map, entry, start);
 	for (current = entry; current->start < end; current = current->next) {
 
 		vm_map_clip_end(map, current, end);
@@ -2572,7 +2598,8 @@
 	 * [Note that clipping is not necessary the second time.]
 	 */
 	for (current = entry; current->start < end;
-	    vm_map_simplify_entry(map, current), current = current->next) {
+	    vm_map_try_merge_entries(map, prev, current),
+	    prev = current, current = prev->next) {
 		if (rv != KERN_SUCCESS ||
 		    (current->eflags & MAP_ENTRY_GUARD) != 0)
 			continue;
@@ -2610,6 +2637,7 @@
 #undef	MASK
 		}
 	}
+	vm_map_try_merge_entries(map, prev, current);
 	vm_map_unlock(map);
 	return (rv);
 }
@@ -2629,7 +2657,7 @@
 	vm_offset_t end,
 	int behav)
 {
-	vm_map_entry_t current, entry;
+	vm_map_entry_t current, entry, prev;
 	bool modify_map;
 
 	/*
@@ -2668,12 +2696,11 @@
 	 */
 	VM_MAP_RANGE_CHECK(map, start, end);
 
-	if (vm_map_lookup_entry(map, start, &entry)) {
-		if (modify_map)
-			vm_map_clip_start(map, entry, start);
-	} else {
-		entry = entry->next;
-	}
+	if (start == 0)
+		prev = &map->header;
+	else
+		vm_map_lookup_entry(map, start - 1, &prev);
+	entry = (prev->end > start) ? prev : prev->next;
 
 	if (modify_map) {
 		/*
@@ -2682,8 +2709,10 @@
 		 * We clip the vm_map_entry so that behavioral changes are
 		 * limited to the specified address range.
 		 */
+		if (prev == entry)
+			prev = _vm_map_clip_start(map, entry, start);
 		for (current = entry; current->start < end;
-		    current = current->next) {
+		    prev = current, current = prev->next) {
 			if (current->eflags & MAP_ENTRY_IS_SUB_MAP)
 				continue;
 
@@ -2714,8 +2743,9 @@
 			default:
 				break;
 			}
-			vm_map_simplify_entry(map, current);
+			vm_map_try_merge_entries(map, prev, current);
 		}
+		vm_map_try_merge_entries(map, prev, current);
 		vm_map_unlock(map);
 	} else {
 		vm_pindex_t pstart, pend;