DeepSpeed ZeRO Offload Host-RAM OOM (SIGKILL -9)
ZeRO CPU/NVMe offload materializes parameters and optimizer states in host RAM on every rank, exhausting system memory and getting the process OOM-killed with no Python traceback.
ZeRO CPU/NVMe offload materializes parameters and optimizer states in host RAM on every rank, exhausting system memory and getting the process OOM-killed with no Python traceback.
What this failure is
DeepSpeed ZeRO Offload Host-RAM OOM (SIGKILL -9) is a Memory failure seen during ML training runs. ZeRO CPU/NVMe offload materializes parameters and optimizer states in host RAM on every rank, exhausting system memory and getting the process OOM-killed with no Python traceback. Common tags: Deepspeed, Zero Offload, Host Ram, Oom.
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Why it happens (the mechanism)
Each rank materializes its params + optimizer states in CPU memory. Pin_memory: true pre-allocates large pinned buffers. Total host memory demand exceeds available RAM. 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
- Process killed with return code -9 and no traceback
- CPU RAM fills up over seconds then the job dies
- Only with ZeRO CPU offload enabled
Common symptoms and what they mean
| Symptom | Why it happens |
|---|---|
| exits with return code = -9 (SIGKILL) | Each rank materializes its params + optimizer states in CPU memory |
| free -h shows CPU RAM dropping toward 0 | pin_memory: true pre-allocates large pinned buffers |
| pin_memory: true in the offload config | Total host memory demand exceeds available RAM |
Which systems are affected
- DeepSpeed ZeRO-2/3 with CPU/NVMe offload
- Large models (33B, T5-11B) on limited host RAM
- 8x ranks each materializing optimizer state
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: exits with return code = -9 (SIGKILL)
- ✓Verified signal present: free -h shows CPU RAM dropping toward 0
- ✓Verified signal present: pin_memory: true in the offload config
- ✓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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Diagnose this failure in VS Code
Select the traceback or open the failed terminal, then run Denpex locally to see the initiating rank, collateral failures, exact fix, and verification command without uploading the log.
Install the free VS Code extensionDeepSpeed errors in context
DeepSpeed changes when parameters, gradients and optimizer state are created, partitioned, gathered and offloaded. The hub separates ZeRO, memory, checkpoint and pipeline failures by lifecycle phase.
Compare every deepspeed error side by sideRelated failures to investigate next
Root cause
- Each rank materializes its params + optimizer states in CPU memory
- pin_memory: true pre-allocates large pinned buffers
- Total host memory demand exceeds available RAM
The fix and how to prevent it
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