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DeepSpeed OOM

DeepSpeed OOM errors occur when ZeRO partitioning, CPU offload, or activation partitioning is misconfigured.

Quick answer

DeepSpeed OOM errors occur when ZeRO partitioning, CPU offload, or activation partitioning is misconfigured.

Root cause
ZeRO stage not aggressive enough. CPU offload not enabled. Activation checkpointing not used.
Recommended fix
Increase ZeRO stage: stage=3 for largest models
How Denpex helps
Denpex investigates DeepSpeed OOM using the evidence you provide or your connected workload collects. Earlier rank, host or application evidence is needed to distinguish an initiating failure from a downstream report.
Memory#deepspeed#zero#offload#memory#training

What this failure is

DeepSpeed OOM is a Memory failure seen during ML training runs. DeepSpeed OOM errors occur when ZeRO partitioning, CPU offload, or activation partitioning is misconfigured. Common tags: Deepspeed, Zero, Offload, Memory.

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Why it happens (the mechanism)

ZeRO stage not aggressive enough. CPU offload not enabled. Activation checkpointing not used. Sub-optimal config for model size. Offload too much to slow storage. 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

  • DeepSpeed training OOMs
  • ZeRO-3 OOM despite offloading
  • DeepSpeed config doesn't reduce memory

Common symptoms and what they mean

SymptomWhy it happens
CUDA OOM with DeepSpeedZeRO stage not aggressive enough
ZeRO-3 still OOMsCPU offload not enabled
CPU offload still OOMsActivation checkpointing not used

Which systems are affected

  • Large model training with DeepSpeed
  • LLM training with ZeRO
  • Memory-efficient training

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: CUDA OOM with DeepSpeed
  • ✓Verified signal present: ZeRO-3 still OOMs
  • ✓Verified signal present: CPU offload still OOMs
  • ✓A targeted fix from the "How to fix it" section eliminates or substantially reduces the symptom within one validation pass.

Root cause

  • ZeRO stage not aggressive enough
  • CPU offload not enabled
  • Activation checkpointing not used
  • Sub-optimal config for model size
  • Offload too much to slow storage

The fix and how to prevent it

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.

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DeepSpeed 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 side

Don't just read the fix, diagnose your run

The encyclopedia tells you what went wrong. Denpex tells you what went wrong in YOUR training run. With your logs, your config, and your stack.