Function vm_object_backing_transfer

freebsd/vm/vm_object.c:809–831

* Transfer a backing reference from backing_object to object. */

 * Transfer a backing reference from backing_object to object.
 */
static void
vm_object_backing_transfer(vm_object_t object, vm_object_t backing_object)
{
	vm_object_t new_backing_object;

	/*
	 * Note that the reference to backing_object->backing_object
	 * moves from within backing_object to within object.
	 */
	vm_object_backing_remove_locked(object);
	new_backing_object = backing_object->backing_object;
	if (new_backing_object == NULL)
		return;
	if ((new_backing_object->flags & OBJ_ANON) != 0) {
		VM_OBJECT_WLOCK(new_backing_object);
		vm_object_backing_remove_locked(backing_object);
		vm_object_backing_insert_locked(object, new_backing_object);
		VM_OBJECT_WUNLOCK(new_backing_object);
	} else {
		object->backing_object = new_backing_object;
		backing_object->backing_object = NULL;
	}
}

/*
 * Wait for a concurrent collapse to settle.