Change SupervisedTrainer decollation default.

[id-b3]

Fixes #8541 .

Description

By default, the SupervisedTrainer has decollation enabled by default. The decollation step moves the tensors to CPU for processing which significantly impacts the speed of each training step as described in issue #8541

This pull request proposes to change the default of decollation to False and provide more information in the documentation as to the impact of the decollation option with regard to the training speed.

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Integration tests passed locally by running ./runtests.sh -f -u --net --coverage.
• Quick tests passed locally by running ./runtests.sh --quick --unittests --disttests.
• In-line docstrings updated.
• Documentation updated, tested make html command in the docs/ folder.

[coderabbitai]

Walkthrough

• monai/engines/trainer.py: Changed SupervisedTrainer init signature default decollate from True to False and updated docstring to reflect the new default and rationale.
• tests/apps/deepgrow/transforms/test_deepgrow_interaction.py: Updated SupervisedTrainer initialization to pass decollate=True.
• tests/integration/test_deepedit_interaction.py: Updated SupervisedTrainer initialization to pass decollate=True.
• tests/testing_data/config_fl_train.json: Added "decollate": true under train.trainer.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Assessment against linked issues

Objective	Addressed	Explanation
Change SupervisedTrainer default decollate to False or warn about slowdown (#8541)	✅

Assessment against linked issues: Out-of-scope changes

None found.

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[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (1)

monai/engines/trainer.py (1)

121-124: Docstring tweak: tighten rationale and guidance.

Small wording improvement; also nudge users when they actually need it.

-            default to `False` as training slows due to tensor movement to CPU for decollation when enabled.
+            default is `False` to avoid the CPU transfer overhead introduced by decollation; enable only when your
+            postprocessing requires list-based transforms from `monai.transforms`.

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Configuration used: .coderabbit.yaml
Review profile: CHILL
Plan: Pro
Knowledge Base: Disabled due to Reviews > Disable Knowledge Base setting

📥 Commits

Reviewing files that changed from the base of the PR and between cafc1fe and acd8ceb.

📒 Files selected for processing (4)

• monai/engines/trainer.py (2 hunks)
• tests/apps/deepgrow/transforms/test_deepgrow_interaction.py (1 hunks)
• tests/integration/test_deepedit_interaction.py (1 hunks)
• tests/testing_data/config_fl_train.json (1 hunks)

🧰 Additional context used

📓 Path-based instructions (1)

**/*.py

⚙️ CodeRabbit Configuration File

Review the Python code for quality and correctness. Ensure variable names adhere to PEP8 style guides, are sensible and informative in regards to their function, though permitting simple names for loop and comprehension variables. Ensure routine names are meaningful in regards to their function and use verbs, adjectives, and nouns in a semantically appropriate way. Docstrings should be present for all definition which describe each variable, return value, and raised exception in the appropriate section of the Google-style of docstrings. Examine code for logical error or inconsistencies, and suggest what may be changed to addressed these. Suggest any enhancements for code improving efficiency, maintainability, comprehensibility, and correctness. Ensure new or modified definitions will be covered by existing or new unit tests.

Files:

• tests/apps/deepgrow/transforms/test_deepgrow_interaction.py
• tests/integration/test_deepedit_interaction.py
• monai/engines/trainer.py

🔇 Additional comments (4)

tests/testing_data/config_fl_train.json (1)

122-124: Config: explicitly enabling decollation is correct for this test bundle.

The added "decollate": true pairs with monai.engines.SupervisedTrainer under train.trainer and matches the new default change. No JSON syntax issues.

monai/engines/trainer.py (1)

157-157: Audit complete – no missing decollate= needed
No Python call sites pass a postprocessing= without also specifying decollate=, and the only config referencing SupervisedTrainer doesn’t use postprocessing. Defaulting decollate=False is safe as-is.

tests/integration/test_deepedit_interaction.py (1)

106-106: LGTM: enabling decollation here is necessary.

Post transforms (Activationsd, AsDiscreted, SplitPredsLabeld, ToTensord) operate per-item; explicitly setting decollate=True preserves existing semantics under the new default.

tests/apps/deepgrow/transforms/test_deepgrow_interaction.py (1)

81-81: LGTM: explicit decollate=True keeps interaction transforms correct.

Iteration transforms include ToNumpyd/ToTensord and discrepancy ops that expect item-wise dicts; this explicit flag is appropriate with the default flipped.