Memory leaks in Node.js cluster's master process

Problem solved, just remove silent property from cluster.setupMaster, then it will not have memory leaks problem, could anyone tell me why it comes like this?

I am working on a project done by Node.js, and when I added cluster to take advantages of multi-CPUs, things go strange.

I fork() worker process from master process, and the thing is my worker process works just fine and do not have a memory leak problem, but master process has it.

The code of master process which using cluster is :

var cluster = require('cluster');
var numCPU = require('os').cpus().length;

cluster.setupMaster({
        exec : '../worker/worker.js',
        silent : true
});

if(cluster.isMaster){
    for(var i=0; i< numCPU;i++){
        cluster.fork();
    }
}