The program of customer directrix load-based demand response (CDL-DR) has advantages of large scale and straightforward implementation, which can play an important role in accommodating large scale renewable energy sources (RES) in electric power grids. In a CDL-DR program, it is crucial to determine the CDL which takes into account both the system operation economics and RES accommodation. First, a novel unit commitment model is developed, which considers not only generating units but also adjustable loads. Specifically, the CDL is determined to minimize generation cost and RES curtailment through joint scheduling of generating units and adjustable loads. Second, a solution method is proposed by combining the cuckoo search algorithm (CSA) and binary particle swarm optimization, which utilizes CSA's powerful global search capability. Finally, the proposed model and method's effectiveness and reasonableness are validated through numerical simulation based on a 36-unit system.