How to save the best checkpoint file?

[Meoooww]

I noticed that the parameter "work-dir" specifies the output path of the checkpoint file, which contains files like "iter_**.pth" and "latest.pth". The "latest.pth" is not the best checkpoint file, so how to output the best checkpoint？

This is my first time using the mmcv， i tried the following code(in segformer.b5.640x640.ade.160k.py), bt useless
evaluation = dict(interval=50, metric='mIoU', save_best='auto')

the mmcv doc: https://mmcv.readthedocs.io/en/v1.3.14/_modules/mmcv/runner/hooks/evaluation.html
ref: open-mmlab/mmsegmentation#130