Long connections with Node.js, how to reduce memory usage and prevent memory leak? Also related with V8 and webkit-devtools

Here is what I'm trying to do: I'm developing a Node.js http server, which will hold long connections for pushing purpose(collaborate with redis) from tens of thousands of mobile clients in a single machine.

Test environment：

1.80GHz*2 CPU/2GB RAM/Unbuntu12.04/Node.js 0.8.16

At the first time, I used "express" module, with which I could reach about 120k concurrent connections before swap being used which means the RAM is not enough. Then, I switched to native "http" module, I got the concurrency up to about 160k. But I realized that there are still too many functionality I don't need in native http module, so I switched it to native "net" module(this means I need to handle http protocol by myself, but that's ok). now, I can reach about 250k concurrent connections per single machine.

Here is the main structure of my code:

var net = require('net');
var redis = require('redis');

var pendingClients = {};

var redisClient = redis.createClient(26379, 'localhost');
redisClient.on('message', function (channel, message) {
    var client = pendingClients[channel];
    if (client) {
        client.res.write(message);
    }
});

var server = net.createServer(function (socket) {
    var buffer = '';
    socket.setEncoding('utf-8');
    socket.on('data', onData);

    function onData(chunk) {
        buffer += chunk;
        // Parse request data.
        // ...

        if ('I have got all I need') {
            socket.removeListener('data', onData);

            var req = {
                clientId: 'whatever'
            };
            var res = new ServerResponse(socket);
            server.emit('request', req, res);
        }  
    }
});

server.on('request', function (req, res) {
    if (res.socket.destroyed) {            
        return;
    }

    pendingClinets[req.clientId] = {
        res: res
    };

    redisClient.subscribe(req.clientId);

    res.socket.on('error', functi