Support device map for distributed autograd while using TensorPipe. (#44859)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44859
TensorPipe's `set_device_map` option was applied during the forward
pass. However, if we ran the backward pass for the graph we would not
automatically pick up the reverse device mapping.
As a result, users had to specify both forward and backward device mapping
which is very tedious to do.
In this PR, I've added this functionality such that TensorPipe automatically
picks up the reverse device mapping during the backward pass. This is done by
storing the appropriate device mapping in the "recv" autograd function for
distributed autograd.
#Closes: https://github.com/pytorch/pytorch/issues/44170
ghstack-source-id: 119950842
Test Plan:
1) waitforbuildbot
2) Unit test added.
Reviewed By: mrshenli
Differential Revision: D23751975
fbshipit-source-id: 2717d0ef5bde3db029a6172d98aad95734d52140
