Running this class:
public class Threads {
  public static void main(String [] args) throws Exception {
    int c = Integer.parseInt(args[0]);
    for (int i = 0; i < c; i++) {
      MyThread t = new MyThread();
      t.start();
    }

    Thread.sleep(5000);
  }

  static class MyThread extends Thread {
    public static Object dummy;
    public void run() {
      try {
        dummy = new byte[0];
        Thread.sleep(10000000);
      } catch (Exception e) {
        e.printStackTrace();
      }
    }
  }
}

with:
java -Xmn3520m -Xms3584m -Xmx3584m -XX:+PrintGC -XX:+PrintGCTimeStamps Threads 64

starts a young GC immediately:
0.075: [GC (Allocation Failure) 2703360K->488K(3219456K), 0.0012880 secs]

-XX:+PrintTLAB gives:
TLAB: gc thread: 0x00007f7204153800 [id: 17869] desired_size: 54067KB slow allocs: 0 refill waste: 865072B alloc: 1.00000 2703360KB refills: 1 waste 100.0% gc: 55364248B slow: 0B fast: 0B