Memory Summary Tool Usage
torch.cuda.memory_summary() helps debug memory issues but output can be overwhelming without understanding it.
torch.
What this failure is
Memory Summary Tool Usage is a Memory failure seen during ML training runs. torch.cuda.memory_summary() helps debug memory issues but output can be overwhelming without understanding it. Common tags: Memory Summary, Debugging, Profiling, Cuda.
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Why it happens (the mechanism)
Memory summary shows allocated, reserved, and active memory. Reserved includes cached memory that can be released. Active memory is what tensors currently use. Snapshot traces allocation history. 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
- Memory summary is hard to interpret
- Memory usage reported doesn't match nvidia-smi
- Cannot identify what's using memory
Common symptoms and what they mean
| Symptom | Why it happens |
|---|---|
| Memory summary shows large reserved memory | Memory summary shows allocated, reserved, and active memory |
| Snapshot shows many small allocations | Reserved includes cached memory that can be released |
| Memory cache size is large | Active memory is what tensors currently use |
Which systems are affected
- Debugging CUDA OOM
- Profiling memory usage
- Optimizing memory allocation
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: Memory summary shows large reserved memory
- ✓Verified signal present: Snapshot shows many small allocations
- ✓Verified signal present: Memory cache size is large
- ✓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
- Memory summary shows allocated, reserved, and active memory
- Reserved includes cached memory that can be released
- Active memory is what tensors currently use
- Snapshot traces allocation history
The fix and how to prevent it
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