Index: vm_map.c
===================================================================
--- vm_map.c
+++ vm_map.c
@@ -2186,8 +2186,19 @@
 	VM_MAP_ASSERT_LOCKED(map);
 	KASSERT(entry->end > start && entry->start < start,
 	    ("_vm_map_clip_start: invalid clip of entry %p", entry));
-	vm_map_simplify_entry(map, entry);
 
+	if ((entry->eflags & MAP_ENTRY_NOMERGE_MASK) == 0 &&
+	    (vm_map_mergeable_neighbors(entry->prev, entry) ||
+	     vm_map_mergeable_neighbors(entry, entry->next))) {
+		printf("%s: simplifying entry start %jx end %jx next_read %jx "
+		    "max_free %jx eflags %jx object-type %d\n", __func__,
+		    (uintmax_t)entry->start, (uintmax_t)entry->end,
+		    (uintmax_t)entry->next_read, (uintmax_t)entry->max_free,
+		    (uintmax_t)entry->eflags,
+		    entry->object.vm_object ? entry->object.vm_object->type : -1);
+		vm_map_simplify_entry(map, entry);
+	}
+
 	/*
 	 * Create a backing object now, if none exists, so that more individual
 	 * objects won't be created after the map entry is split.
@@ -2472,9 +2483,7 @@
 
 	VM_MAP_RANGE_CHECK(map, start, end);
 
-	if (vm_map_lookup_entry(map, start, &entry)) {
-		vm_map_clip_start(map, entry, start);
-	} else {
+	if (!vm_map_lookup_entry(map, start, &entry)) {
 		entry = entry->next;
 	}
 
@@ -2515,6 +2524,8 @@
 	 * now will do cow due to allowed write (e.g. debugger sets
 	 * breakpoint on text segment)
 	 */
+	if (entry->start < start)
+		vm_map_clip_start(map, entry, start);
 	for (current = entry; current->start < end; current = current->next) {
 
 		vm_map_clip_end(map, current, end);