Activation Checkpointing Compatibility
Activation checkpointing compatibility issues arise when using torch.compile, FSDP, or DDP with checkpointing.
Activation checkpointing compatibility issues arise when using torch.
What this failure is
Activation Checkpointing Compatibility is a Memory failure seen during ML training runs. Activation checkpointing compatibility issues arise when using torch.compile, FSDP, or DDP with checkpointing. Common tags: Activation Checkpointing, Torch Compile, Fsdp, Ddp.
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Why it happens (the mechanism)
Use_reentrant=True deprecated with torch.compile. Checkpointing on non-compat layers. Torch.utils.checkpoint vs FSDP checkpoint. Activation recomputation in distributed training. Taken together, these mechanisms explain why the failure is reproducible, why it tends to surface on specific workloads or scales, and why generic mitigation attempts often fall short without addressing the underlying cause.
What you'll observe
- Activation checkpointing doesn't work with torch.compile
- Checkpointing causes errors with FSDP
- Checkpointing fails with DDP
Common symptoms and what they mean
| Symptom | Why it happens |
|---|---|
| use_reentrant=True breaks torch.compile | use_reentrant=True deprecated with torch.compile |
| Checkpointing not applied to all layers | Checkpointing on non-compat layers |
| Checkpointing wrong layer type | torch.utils.checkpoint vs FSDP checkpoint |
Which systems are affected
- Training with torch.compile and gradient checkpointing
- FSDP with checkpointing
- DDP with checkpointing
How to confirm this is the problem
Use this checklist to test the hypothesis against a small reproduction. No single line proves the root cause, so preserve the preceding events and compare one variable at a time.
- ✓Reproduce the failure from a clean checkpoint/seed: the symptom must appear without warm-up state from a previous run.
- ✓Verified signal present: use_reentrant=True breaks torch.compile
- ✓Verified signal present: Checkpointing not applied to all layers
- ✓Verified signal present: Checkpointing wrong layer type
- ✓A targeted fix from the "How to fix it" section eliminates or substantially reduces the symptom within one validation pass.
The fix and the prevention pattern
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Root cause
- use_reentrant=True deprecated with torch.compile
- Checkpointing on non-compat layers
- torch.utils.checkpoint vs FSDP checkpoint
- Activation recomputation in distributed training
The fix and how to prevent it
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