[DDP] Custom buffer reduction (#64513)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/64513
Proposal: https://github.com/pytorch/pytorch/issues/63041
Support custom buffer reduction in DDP via hook
ghstack-source-id: 138655663
Test Plan: CI
Reviewed By: SciPioneer
Differential Revision: D30751152
fbshipit-source-id: 257a9d46bb178d8812d4ea5a4d9c6140b8a1791f
