Remove parent device mesh check (#118620)
Removes raising error if a device_mesh has a parent.
The comment says that HSDP + TP is not supported, but I'm able to do 2D parallelism + HSDP fine. The only issues are:
- this check
- https://github.com/pytorch/pytorch/pull/118618
- a series of PRs related to checkpointing with 3D meshes that I will open
We currently monkeypatch for the above which I am slowly upstreaming.
I imagine torch will have a better, native integration eventually, but this check seems too aggressive in the meantime given DTensor now lets users do some things themselves (which is amazing 🎉)!
Pull Request resolved: https://github.com/pytorch/pytorch/pull/118620
Approved by: https://github.com/Skylion007
