memory from transport buffer not freed after connection_lost

Start by running the supplied Python reproduction with uvloop.new_event_loop, first observing memory after the telnet session closes and then comparing it with the stock asyncio runner. Trace the transport buffer and connection_lost path; done means memory is released after disconnect as it is under asyncio.

• uvloop version: 0.17.0
• Python version: 3.11.4
• Platform: fedora 38
• Can you reproduce the bug with PYTHONASYNCIODEBUG in env?: yes, with PYTHONASYNCIODEBUG=1
• Does uvloop behave differently from vanilla asyncio? How?: yes, keeps resident memory

If I flood transport.write() and then close the connection (e.g. having the client telnet session stop) the memory stays resident.
Under stock asyncio, the memory immediately is released.

To reproduce,

1. start this program,
2. watch it in top
3. , telnet to port 8888,
4. watch memory usage spike.
5. close the telnet session,
6. see that memory usage stays high.
7. repeat this experiment with stock asyncio runner,
8. the memory is freed immediately. after telnet session is closed

This test script is a malloc bomb, so make sure you watch memory closely or you will consume all the memory on your machine

#!/usr/bin/env python3


import asyncio
import uvloop


class EchoServerProtocol(asyncio.Protocol):
    def __init__(self, on_connect, on_disconnect):
        self.on_connect = on_connect
        self.on_disconnect = on_disconnect

    def connection_lost(self, transport):
        print('Connection lost')
        self.on_disconnect()
        self.transport = None

    def connection_made(self, transport):
        self.on_connect(transport)
        peername = transport.get_extra_info('peername')
        print('Connection from {}'.format(peername))
        self.transport = transport

    def data_received(self, data):
        message = data.decode()
        print('Data received: {!r}'.format(message))

        print('Send: {!r}'.format(message))
        self.transport.write(data)

        print('Close the client socket')


async def send_data(transport):
    message = b'Hello World!' * 1000
    while True:
        transport.write(message)
        await asyncio.sleep(0)


task = None


def on_connect(transport):
    global task
    task = asyncio.create_task(send_data(transport))


def on_disconnect():
    global task
    task.cancel()


async def start():
    # Get a reference to the event loop as we plan to use
    # low-level APIs.
    loop = asyncio.get_running_loop()

    server = await loop.create_server(
        lambda: EchoServerProtocol(on_connect, on_disconnect),
        '127.0.0.1',
        8888,
    )

    async with server:
        await server.serve_forever()


if __name__ == '__main__':
    # with asyncio.Runner() as runner:
    with asyncio.Runner(loop_factory=uvloop.new_event_loop) as runner:
        runner.run(start())