def calcMemUsage(counters):
    """
    Calculate system memory usage
    :param counters: dict, output of readMemInfo()
    :return: system memory usage
    """
    used = counters['total'] - counters['free'] - \
        counters['buffers'] - counters['cached']
    total = counters['total']
    # return used*100 / total
    return used / total