def METHOD_NAME(self):
    """how much of memory can be trimmed to reduce computation"""
    L = self._max_span
    trim_len = min(L - 1, L - self._mask.get_current_max_size())
    # too fine granularity might be bad for the memory management
    trim_len = math.floor(trim_len / 64) * 64
    return trim_len