* [fx] add some comment and docstrings.
* [fx] add dataflow analysis for an autograd graph.
* add intepretation for graph analysis.
* [fx] before doing save_tensor_hooks.
* [fx] provide an accurate estimation of memory except for GPT-2.
* [fx] provide an accurate estimation of memory except for GPT-2.
* [fx] provide an accurate estimation of memory except for GPT-2.
* [fx] a very accurate version on GPT-2.
* [fx] refactor code.
* [fx] remove redundant inplace=True.
* [fx] refactor code.
* [fx] refactor code.
* [fx] refactor code.
* [fx] dive into backward memory.
Super Daniel