Thank you, @apaszke, I think I start to understand (sorry, I’m slow…).
Could you give me a hint about these “better ways” you are referring at? I’m just super curious now 
Answering you question “Why do you even need to know what Module instantiated which Function?” is pretty simple: so that I know to which Moudle I should register a forward hook in order to inspect the Tensor's flow in the graph.
Even better, would it make sense to have a register_forward/backward_hook() for the Variable class instead of the current register[_backward]_hook()?