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A CUDA out-of-memory (OOM) error on an RTX Spark laptop has two common causes: the model, context, or concurrent requests need more memory than the workload can allocate, or the system’s unified memory is under pressure from the CPU, GPU, and filesystem cache together. Start by identifying whether the failure occurs while loading weights, creating the KV cache, or initializing CUDA. Then either reduce the model’s memory demand (smaller model, FP8/FP4 quantization, shorter context, fewer sequences) or clear unified-memory pressure and restart the workload.

This distinction matters because Spark systems based on GB10 unified memory can report confusing availability. A machine may appear to have free capacity while allocations still fail, and nvidia-smi may show unsupported or incomplete fields. The workflow below covers LM Studio, vLLM, Linux diagnostics, cache recovery, and durable settings changes.

What does CUDA out of memory mean on an RTX Spark laptop?

CUDA OOM means that a CUDA allocation requested by the model runtime could not be satisfied at that moment. It does not necessarily mean that the model weights alone are larger than the laptop’s advertised memory. Weight storage, the KV cache for the active context, multiple simultaneous sequences, temporary workspaces, the operating system, and filesystem cache all draw from available memory.

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RTX Spark and DGX Spark systems use a unified memory architecture (UMA). NVIDIA describes UMA as dynamic sharing between GPU and CPU memory. On a GB10 system, CPU allocations, GPU allocations, and filesystem cache compete for the same DRAM rather than residing in separate pools. Spark configurations can provide up to 128 GB of unified memory, but that capacity is shared and is not a guarantee that every model or context setting will fit.

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Identify the allocation stage first

  • Weight-loading failure: the runtime cannot place the model’s parameters in memory. A smaller model or lower-memory quantization is the direct remedy.
  • KV-cache failure: weights load, but the requested context length or batch of sequences cannot be allocated. Reduce context length and concurrency.
  • CUDA-initialization failure: the runtime fails before useful model work begins. Other processes, stale allocations, or unified-memory pressure are more likely causes.
  • Mid-generation failure: a longer prompt, growing conversation, larger batch, or additional request pushed the working set over the available limit.

Save the complete traceback before changing settings. The wording and timing usually reveal which branch to follow.

What should I do in the first five minutes?

  1. Record the exact error. Note the application, model file, quantization, context setting, number of active requests, and whether the failure happened at startup or during generation.
  2. Stop competing workloads. Close other model servers, notebooks, GPU applications, containers, and large data-processing jobs. On UMA, a CPU-heavy application can consume memory that the GPU needs.
  3. Confirm the model settings. Check the model’s quantization and context length in the launcher. Do not assume that a model’s parameter count is its entire memory requirement.
  4. Check system memory. Run free -h. For more detail, inspect /proc/meminfo, especially MemAvailable, Cached, SReclaimable, and buff/cache.
  5. Retry once after cleanup. If the machine is under cache pressure, flush clean caches using the command in the unified-memory section below, then restart the affected application.

This short triage separates a workload that fundamentally does not fit from one that failed because the system was temporarily crowded.

How do I fix a model-loading OOM in LM Studio?

When LM Studio reports CUDA OOM while loading a model, first switch to a smaller model or a different, lower-memory quantization. NVIDIA’s guidance specifically points to FP8 or FP4 quantization, or to choosing a smaller model, when the allocation cannot fit.

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LM Studio recovery steps

  1. Stop the failed load and return to the model selector.
  2. Choose a smaller parameter-size model, or select an FP8/FP4 build when one is available for the model family.
  3. Load the replacement with no other local model server running.
  4. After it loads, test a short prompt before restoring a long context or additional sessions.
  5. If the smaller model succeeds, increase context or concurrency gradually until you find the operating limit.

Lower-precision quantization reduces allocation pressure, but it is a quality trade-off: outputs can differ from a higher-precision build. Keep the original model available for tasks where quality is more important, and use the smaller or lower-precision build for workloads that must remain resident.

Which vLLM settings reduce memory use?

In vLLM, the most direct controls are --max-model-len for context capacity and --max-num-seqs for concurrent sequences. Lowering either reduces the amount of KV-cache memory that vLLM reserves. NVIDIA’s vLLM guidance also identifies --gpu-memory-utilization as a setting to lower when diagnosing capacity and KV-cache allocation failures.

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Apply the settings in the launch command

Edit the command that starts your server. For example:

vllm serve MODEL_NAME --max-model-len 4096 --max-num-seqs 1 --gpu-memory-utilization 0.8

The values above are a conservative starting example, not a benchmark or universal limit. Replace them with settings appropriate for your model and workload. Change one variable at a time so you can tell which adjustment solved the failure.

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Understand the trade-offs

Change Memory effect What you give up
Smaller model Fewer weights and generally lower runtime allocation Potentially lower reasoning, knowledge, or instruction-following quality
FP8 or FP4 quantization Lower weight footprint than a higher-precision build Possible output-quality or compatibility differences
Lower --max-model-len Smaller maximum KV cache Shorter prompts and conversations
Lower --max-num-seqs Fewer simultaneous KV caches Lower serving concurrency and throughput
Lower --gpu-memory-utilization Restricts the fraction vLLM targets during allocation Less usable headroom for the model and cache; test carefully because an overly low value can prevent startup

If weights load but the server fails when it creates the cache, change context length and sequence concurrency before replacing the model. If weights themselves cannot load, those flags cannot make the parameter storage disappear; use a smaller model or lower-memory quantization.

Why does CUDA OOM happen when my Spark laptop still appears to have memory available?

UMA accounting is the usual explanation. Free memory shown by a GPU-oriented tool may not equal memory that the operating system can immediately hand to a new allocation. CPU pages, reclaimable kernel structures, filesystem cache, pinned buffers, and existing CUDA allocations all affect whether a request succeeds.

Inspect the Linux memory view

Run:

free -h

Then inspect the relevant fields:

grep -E 'MemAvailable|Cached|SReclaimable|Buffers|MemFree' /proc/meminfo

MemAvailable is a better indicator of memory that can be allocated without swapping than MemFree alone. A large Cached, SReclaimable, or buff/cache value indicates reclaimable system data may be contributing to pressure, although cache is not automatically a problem. Look for the combination of low available memory, a large cache, and an OOM that disappears after a restart.

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Flush clean caches as a diagnostic recovery step

After stopping the workload, run:

sudo sh -c 'sync; echo 3 > /proc/sys/vm/drop_caches'

The sync operation writes pending filesystem data before clean page-cache entries are discarded. This command is a temporary diagnostic measure, not a permanent tuning strategy. Restart the affected model application after it completes; otherwise, the process may retain its previous allocations or fail to reinitialize cleanly.

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NVIDIA documents cache flushing as a recovery step for UMA memory pressure. If the same model repeatedly fails after a clean restart and with caches low, treat the problem as a capacity or configuration issue rather than relying on repeated cache drops.

Can I trust nvidia-smi on a unified-memory Spark system?

Use nvidia-smi and its per-process information, but interpret the output differently from a discrete-GPU workstation. On UMA systems, some query fields can show N/A, and the summary may display Memory-Usage: Not Supported. That is expected behavior for this architecture and does not prove that no memory is available.

CUDA-level reporting can also under-report usable memory. NVIDIA’s vLLM guidance notes that cudaMemGetInfo and related query fields may not reflect the full UMA state. When the GPU report conflicts with the Linux memory view, use both: inspect processes with nvidia-smi, then verify system pressure with free -h and /proc/meminfo.

What a useful diagnostic record contains

  • The full application traceback and the command used to launch it.
  • Model name, parameter size, quantization format, context limit, and active sequence count.
  • Output of free -h and the relevant /proc/meminfo fields before and after the failure.
  • Plain nvidia-smi output, including any N/A or unsupported memory fields.
  • Whether stopping other applications, flushing clean caches, or rebooting changed the result.

How should I balance model quality, context, and throughput?

There is no setting that increases every dimension at once. More model parameters can improve capability but consume more memory; longer context increases the KV cache; and more concurrent sequences improve throughput only while enough memory remains for each additional cache.

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Priority Preferred adjustment Cost
Keep the best possible model quality Keep the model and reduce context length or concurrent sequences first Shorter conversations or fewer simultaneous users
Fit a model that currently will not load Choose a smaller model or FP8/FP4 quantization Potential quality or capability reduction
Support more simultaneous requests Lower per-request context and increase concurrency only in small steps Less history per request and a higher risk of cache pressure
Recover from a one-time failure Stop workloads, flush clean caches, and restart No durable increase in model capacity
Run larger local models Use a Spark configuration with more unified memory, up to the stated 128 GB maximum for supported configurations Higher hardware cost and reduced portability; shared memory still includes the operating system and caches

Use the smallest change that meets your goal. For a single-user assistant, reducing context is often less disruptive than changing the model. For a multi-user server, sequence concurrency is usually the first variable to cap.

Does more unified memory let me run any larger local model?

More unified memory expands the set of models and contexts that can fit, but it does not eliminate OOM conditions. The operating system, filesystem cache, runtime workspaces, KV cache, and concurrent requests still consume the same pool. A model that fits at startup can fail later when a conversation grows or another sequence is admitted.

Capacity also depends on the runtime and quantization. Two builds of the same model can have different footprints, and a server configured for a long maximum context may reserve substantially more memory than a short-context single-user session. Treat the advertised capacity as a ceiling for the whole machine, not as VRAM dedicated exclusively to model weights.

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Should I update the Spark software before troubleshooting further?

Yes. Keep the Spark operating system, NVIDIA driver, and model-serving containers current. NVIDIA’s July 2026 release notes report improved GB10 unified-memory OOM handling and better user feedback during memory pressure. Updating can therefore change both recovery behavior and the diagnostic information you see.

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Update safely

  1. Record your current driver, OS, container image, and model command so you can reproduce the issue.
  2. Apply the vendor’s current OS and driver updates, then update the serving container or application through its normal channel.
  3. Reboot after a driver or kernel change.
  4. Retest with the same model, quantization, context, and concurrency before changing additional variables.

An update is not a substitute for an oversized workload. If the same allocation fails with a clean, current system, return to the model-size, context, concurrency, and UMA-pressure branches.

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What is the complete decision path for a recurring OOM?

  1. Classify the failure stage. Loading weights points to model footprint; cache creation or generation points to context and concurrency; initialization points to system pressure or stale state.
  2. Reproduce with competing workloads stopped. This establishes whether another process is consuming the shared pool.
  3. Reduce demand. Try a smaller model or FP8/FP4 quantization for weight failures. For vLLM, lower --max-model-len and --max-num-seqs; adjust --gpu-memory-utilization when diagnosing allocation limits.
  4. Check UMA pressure. Use free -h and /proc/meminfo, paying attention to available memory and reclaimable cache.
  5. Flush and restart once. Run the cache-drop command only after synchronizing data and stopping the workload.
  6. Verify with both monitoring views. Compare Linux memory data with nvidia-smi, allowing for unsupported UMA fields.
  7. Update the software stack. Install current Spark OS, driver, and container updates, including the July 2026 GB10 UMA improvements where applicable.
  8. Make the durable choice. Keep the reduced settings, change the model, or move to a higher-capacity Spark configuration instead of repeatedly clearing caches.

The durable fix is the one that leaves enough shared memory for the model and the rest of the machine under the workload you actually run. Cache clearing can recover a temporarily pressured system; it cannot make an oversized model, context, or concurrency setting fit indefinitely.

Frequently Asked Questions

Why does the same model sometimes load successfully and fail later?

The memory footprint can change after startup as the conversation grows, a second sequence is admitted, or another application fills the shared UMA pool. A successful initial load therefore proves only that the initial weights and cache reservation fit at that moment.

Is clearing Linux caches a permanent fix for CUDA OOM?

No. Dropping clean caches can recover reclaimable DRAM and confirm that UMA pressure was involved, but the cache will be rebuilt and the underlying workload still has the same requirements. Persistent failures need lower demand or a different model configuration.

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Should I choose FP8 or FP4 for local inference?

Both reduce memory pressure compared with higher-precision weights, but the practical choice depends on which quantized build your runtime supports and how much output-quality variation your task tolerates. Test the exact model build with representative prompts rather than assuming the formats are interchangeable.

Can a laptop with 128 GB of unified memory run every large language model locally?

No. The 128 GB figure is shared by the CPU, GPU, operating system, filesystem cache, model weights, KV cache, and runtime overhead. Context length, concurrent sequences, quantization, and software behavior can still produce OOM errors below that headline capacity.

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