'Called with the currently active and spilled paths to spill some
paths. Should return the new active and spilled paths.'

def spill_paths(self, active, spilled):

    l.debug('spill_paths    received    %d    active    and    %d    spilled    paths.', len(active), len(spilled))
    prioritized = self.prioritize_paths((active + spilled))
    new_active = prioritized[:self._max_active]
    new_spilled = prioritized[self._max_active:]
    l.debug('...    %d    active    and    %d    spilled    paths.', len(new_active), len(new_spilled))
    return (new_active, new_spilled)
