NodeJS with Socket.IO 1.0 - memory leak outside of heap

We've been trying to deploy a small NodeJS app using Socket.IO and have been running into a problem where while the heap size of the app remains fairly acceptable, the total memory used (rss) creeps up to over 2gb after around 2 hours, and continues to rise.

In an effort to make sure the problem wasn't in our code, we deployed a bare bones app with no custom logic apart from initializing Socket IO. We ran that against the same production traffic, and experienced the same issue.

Every 10 seconds we output the following data: rss memory usage, heap total, heap count, and connection count. Here's a sample of the output:

523898880 199490816 123040352 2001
537059328 209774080 163828336 2011
538578944 206714368 150879848 2031
535252992 199514880 156743280 2041
542162944 200522752 145077944 2039
539652096 195387136 129486792 2055
551006208 206726400 170918304 2070
553254912 205706496 156447496 2071
550584320 198482944 154005496 2076
564363264 209810176 140442920 2095
561176576 201578752 123214232 2118
562487296 200546816 110638376 2112
572096512 206714368 162713240 2133
569552896 200546816 147439016 2121
577777664 205682432 136653448 2115
582496256 207770368 121204056 2133
582909952 205706496 115449888 2153
597364736 215989760 164582600 2158
590491648 204686592 148962008 2158
598315008 209810176 137608840 2164
598249472 205718528 123472944 2188
607158272 211898112 160187496 2168
609869824 210866176 154986472 2161
618110976 214969856 142425488 2180
615014400 207782400 119745816 2188
623575040 214981888 163602944 2180
624717824 210842112 147051160 2189
627556352 210866176 142542800 2191
636477440 216013824 129968776 2203
643809280 221149440 162858408 2219
644407296 217057792 154994536 2224
642068480 211922176 141626008 2240
649084928 214969856 123126792 2267
662454272 224233216 166539024 2272
659439616 217045760 162742688 2258
662867968 217057792 137425392 2266
667013120 218065664 119616592 2261
673230848 220129536 172101080 2272
677904384 220129536 149771776 2267
676691968 217045760 129936448 2267
674639872 211898112 125941816 2277
689025024 223225344 163745856 2274
689991680 219109632 151478936 2282
698601472 225301248 137102712 2298
706170880 229428992 171321288 2306
705675264 224257280 160088496 2303
701198336 217033728 149326384 2313
701833216 216013824 129806072 2314
718053376 227365120 184078288 2335
718950400 223225344 157977312 2333
717037568 218065664 146137456 2354
714428416 210890240 136566344 2381

As you can see, in a fairly short amount of the time the total memory usage increased by 200mb, even though the connection count only increased by around 400. The heap usage remained roughly the same, just a bit higher to account for the higher connection count.

We're running on Debian Wheezy on 64bit. NodeJS version is 0.10.29, and Socket IO version is 1.0.6. The code we're using is:

var http = require('http'),
    io = require('socket.io');

var app = http.createServer();
var server = io(app);
app.listen(80);
var connections = 0;

server.on('connection', function(socket) {
    connections++;

    socket.on('disconnect', function() {
        connections--;
    });
});

setInterval(function() {
    var mem = process.memoryUsage();
    console.log(mem.rss + ' ' + mem.heapTotal + ' ' + mem.heapUsed + ' ' + connections);
}, 10000);

Is there any way we can find out why Node is using so much memory in total, or any way to see what's happening outside of the heap to try and find the memory leak? We've already tried all of the usual tricks for checking heap usage and found nothing, but did not expect to since the problem doesn't seem to be with memory on the heap.