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[Docs] --offload-train is not forced by --colocate, and skipping it took a step from 18.85 s to 3.32 s - #445

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@0z5a 0z5a commented Sep 19, 2026 •

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Incremental review: Files changed.

Base: 0z5a-branch at 791f101e20db377b28e15f12a00863baaea2605f.

Correct --offload-train help: --colocate enables offload when the argument is unset, while explicit --no-offload-train is honored. Explain that a resident actor requires enough GPU memory for the rollout engine alongside training state.

Comment/help changes only. Seven steady Qwen3-0.6B rollouts per configuration on one colocated GPU, with the same workload and vLLM memory budget:

Metric Default offload --no-offload-train Observed ratio
Step time 18.853 s 3.316 s 5.686×
Sleep / wake-up 11.228 / 3.773 s — —
Train wait 17.425 s 2.486 s —
Train time 0.864 s 0.815 s —

This measures an existing configuration choice, not acceleration caused by the help change. Default-selection policy is discussed in #442.

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Code Review

This pull request updates the argument parsing and validation logic in vime/utils/arguments.py to clarify and document the behavior of the --offload-train option when --colocate is enabled. Specifically, it updates the help text and adds a detailed code comment explaining that while training offloading defaults to true under colocation, an explicit --no-offload-train flag is honored if both the training state and rollout engines fit in device memory, which significantly improves step performance by skipping the memory-saver copy. There are no review comments to address, and I have no additional feedback to provide.

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read-the-docs-community Bot commented Sep 19, 2026 •

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@0z5a
0z5a force-pushed the docs/colocate-offload-train-help branch from e5736a4 to 8a481d2 Compare September 24, 2026 06:54
The help text for --offload-train says "This will always be true when --colocate
is set", but the code only defaults it to true when it is unset, and an explicit
--no-offload-train is honoured. The difference matters: with the offload on, the
memory-saver copy dominates the step, and skipping it when the training state and
the rollout engines both fit in device memory took the step from 18.85 s to
3.32 s on 1 GPU with Qwen3-0.6B (same workload, same vLLM memory budget, 7
steady rollouts each).

Say what the flag actually does, and note the trade-off where the colocate
default is applied.

No behaviour change.

Signed-off-by: 0z5a <0z5a@users.noreply.github.com>
Signed-off-by: 0z5a <dezhen.lu@student.uni-tuebingen.de>
@0z5a

0z5a commented Oct 6, 2026

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Superseded by #460, now merged into 0z5a-branch. The consolidated implementation and validation are retained there; closing this duplicate PR.

@0z5a 0z5a closed this Oct 6, 2026
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