Disable memory sharing on model parameters in ddp-spawn #18238
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Co-authored-by: Carlos Mocholí <carlossmocholi@gmail.com>
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Co-authored-by: Carlos Mocholí <carlossmocholi@gmail.com> Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com> (cherry picked from commit a0ca2c8)
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Co-authored-by: Carlos Mocholí <carlossmocholi@gmail.com> Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com> (cherry picked from commit a0ca2c8)
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What does this PR do?
Fixes #17399
The
torch.multiprocessing.spawnlauncher (strategy="ddp_spawn") by default enables memory sharing for all tensors passed through the spawning function, including tensors in modules. This means that the underlying storage of these tensors is shared across all processes, and anyone can read or write to them. This can lead to inconsistencies, as demonstrated in the repro example in the linked issue. This PR disables that by cloning the weights in each process, detaching it from shared memory.Note:
This only applies when running on CPU. If running on GPU, memory won't be shared.
Hopefully, this will also help to avoid flakiness in tests.
cc @Borda @carmocca @justusschock @awaelchli