We should know something before converting to serving model
**inference_model_dir**:the directory of Paddle inference model
**serving_client_dir**: the directory of server side configuration
**serving_client_dir**: the directory of client side configuration
**model_filename**: this is model description file whose default value is `__model__`, if it's not default name, set `model_filename` explicitly
**params_filename**: during `save_inference_model` every Variable will be save as a single file. If we have the inference model whose params are compressed into one file, please set `params_filename` explicitly