code: private IOStat getIOStat(final int nodeid) {
  		IOStat io = iostats.get(nodeid);
  		if (io == null) {
  			io = new IOStat(nodeid);
  			iostats.put(nodeid, io);
  		}
  		return io;
  	}
docs: Return or Create if not exist an IOStat object for a nodeid
  
  @param nodeid
  @param isLeaf
  @return IOStat object