The reduce keyword was implemented after 0.2. To use it, you should build from source or wait for the upcoming 0.3 release.
Alternatively, you can write your own SmoothL1Loss in Python. It’s not too bad, you can try something like this: https://github.com/zou3519/pytorch/blob/ff4612605e0c311c1f6ad2d6a67a298587ea8eae/test/common_nn.py#L299 23