Fix how SimpleFSDP get the nD mesh #1959
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Stack from [ghstack](https://github.com/ezyang/ghstack/tree/0.12.0) (oldest at bottom): * #1960 * #1959 * __->__ #1963 pytorch/pytorch#166130 changes the configs and this PR adopts the new configs Squash and Merge button won't work for this PR. I'll merge by myself.
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Stack from [ghstack](https://github.com/ezyang/ghstack/tree/0.12.0) (oldest at bottom): * #1960 * #1959 * __->__ #1965 **Squash and Merge button won't work for this PR. I'll merge by myself.** #1963 was accdientally merge with Squash and Merge button. This is a reland PR.
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| assert inner_mesh.mesh_dim_names is not None | ||
| submesh_names = outer_mesh.mesh_dim_names + inner_mesh.mesh_dim_names | ||
| spanned_mesh = outer_global_mesh[submesh_names] | ||
| spanned_mesh = DeviceMesh._concatenate((outer_mesh, inner_mesh)) |
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Nice!
One nit: isn't the argument supposed to be a list, and not a tuple?
If so, how come there is no type checking or other linting to catch this?
Note that we've already observed TorchTitan being somewhat incorrect with types, e.g., it passes lists to init_device_mesh instead of tuples.
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Good point, I believe we have not enabled type checking for TorchTitan, which we should.
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Stack from [ghstack](https://github.com/ezyang/ghstack/tree/0.12.0) (oldest at bottom): * __->__ #1960 * #1959 As title, no logic change. **Squash and Merge button won't work for this PR. I'll merge by myself.**
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Stack from ghstack (oldest at bottom):
This is the recommended way to get the nD mesh now that DeviceMesh has _concatenate().
Squash and Merge button won't work for this PR. I'll merge by myself.