code: private void onHit(Node node) {
      policyStats.recordHit();
  
      int newCount = node.freq.count + 1;
      FrequencyNode freqN = (node.freq.next.count == newCount)
          ? node.freq.next
          : new FrequencyNode(newCount, node.freq);
      node.remove();
      if (node.freq.isEmpty()) {
        node.freq.remove();
      }
      node.freq = freqN;
      node.append();
    }
docs: Moves the entry to the next higher frequency list, creating it if necessary.