add simple memory analyzer and log warning if GPU underutilized (#21024)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21024
Add a new pybinded call to CUDAGetMemoryInfo.
Reviewed By: wesolwsk
Differential Revision: D15520607
fbshipit-source-id: f6d04e48f7d7cb089fc52fa8835cfee3f452d2f1
