memory leak with tonardo

[qianyi3210]

my application use pyzmq work with tornado, main work is just like a task center.
The memory will increase into 6G when task is busy, but when i stop task request and after all zmq task finished, the memory only reduce to 3.9g. i use gc.set_debug(DEBUG_LEAK) and find many objects can't be released.
<cell at 0x7fa3b33389f0: weakproxy object at 0x7fa3d88aafc8>,
<cell at 0x7fa3b3338ec0: function object at 0x7fa3d0ac52a8>,
<cell at 0x7fa3b33382f0: function object at 0x7fa3d0ac5aa0>
python:2.7.5
tornado:4.5.2
pyzmq:17.0.0
code as below:

    loop = ZMQIOLoop()
    loop.install()
    context = zmq.Context()
    zmq_publish = context.socket(zmq.PUB)
    zmq_publish.bind("tcp://127.0.0.1:%s" % CommonConstants.ZMQ_PUBLISH_PORT)
    zmq_dispatch = context.socket(zmq.REP)
    zmq_dispatch.bind("tcp://127.0.0.1:%s" % CommonConstants.ZMQ_DISPATCH_PORT)
    zmq_result = context.socket(zmq.PULL)
    zmq_result.bind("tcp://127.0.0.1:%s" % CommonConstants.ZMQ_RESULT_PORT)

    receiver = ZMQStream(zmq_result)
    receiver.on_recv(on_worker_data_in)

    dispatch_stream = ZMQStream(zmq_dispatch)
    dispatch_stream.on_recv(dispatch_recv)
    web.Application([
        (r'/api/v1/sync/(cli|snmp|all)', CommandApiHandler),
           ], autoreload=False).listen(port)
    try:
        ioloop.IOLoop.instance().start()
    except KeyboardInterrupt:
        pass