Index: vm_map.c
===================================================================
--- vm_map.c
+++ vm_map.c
@@ -2453,6 +2453,7 @@
 	vm_map_entry_t current, entry, in_tran;
 	vm_object_t obj;
 	struct ucred *cred;
+	vm_ooffset_t to_reserve;
 	vm_prot_t old_prot;
 
 	if (start == end)
@@ -2460,6 +2461,7 @@
 
 again:
 	in_tran = NULL;
+	to_reserve = 0;
 	vm_map_lock(map);
 
 	/*
@@ -2472,9 +2474,7 @@
 
 	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;
 	}
 
@@ -2494,7 +2494,22 @@
 		}
 		if ((entry->eflags & MAP_ENTRY_IN_TRANSITION) != 0)
 			in_tran = entry;
+		if (set_max ||
+		    ((new_prot & ~(current->protection)) & VM_PROT_WRITE) == 0 ||
+		    ENTRY_CHARGED(current)) {
+			continue;
+		}
+		obj = current->object.vm_object;
+		if (obj == NULL ? (current->eflags & MAP_ENTRY_NEEDS_COPY) :
+		    (obj->type == OBJT_DEFAULT || obj->type == OBJT_SWAP)) {
+			to_reserve += ulmin(end, current->end) -
+			    ulmax(start, current->start);
+		}
 	}
+	if (!swap_reserve(to_reserve)) {
+		vm_map_unlock(map);
+		return (KERN_RESOURCE_SHORTAGE);
+	}
 
 	/*
 	 * Postpone the operation until all in transition map entries
@@ -2515,6 +2530,8 @@
 	 * 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);
@@ -2530,10 +2547,6 @@
 		obj = current->object.vm_object;
 
 		if (obj == NULL || (current->eflags & MAP_ENTRY_NEEDS_COPY)) {
-			if (!swap_reserve(current->end - current->start)) {
-				vm_map_unlock(map);
-				return (KERN_RESOURCE_SHORTAGE);
-			}
 			crhold(cred);
 			current->cred = cred;
 			continue;
@@ -2553,12 +2566,6 @@
 		KASSERT(obj->charge == 0,
 		    ("vm_map_protect: object %p overcharged (entry %p)",
 		    obj, current));
-		if (!swap_reserve(ptoa(obj->size))) {
-			VM_OBJECT_WUNLOCK(obj);
-			vm_map_unlock(map);
-			return (KERN_RESOURCE_SHORTAGE);
-		}
-
 		crhold(cred);
 		obj->cred = cred;
 		obj->charge = ptoa(obj->size);