why does child memory keep growing?

ipc.js

var cp = require('child_process');

if (!process.send) {
  // master
  var child = cp.fork('./test.js');
  child.on('message', function (msg) {
    process.stdout.write(msg);
  });
} else {
  // child
  while (true) {
    process.send('hey there\n');
  }
}