Cycles GPU out-of-memory allocation failure: measuring texture vs. geometry VRAM pressure before optimization

Identifying the dominant VRAM consumer

Cycles GPU allocation failures happen when the GPU runs out of VRAM. To decide whether textures, geometry, or BVH data are the culprit, you need a reliable snapshot of the memory usage per category for the backend you are using.

1. Enable Cycles device‑memory stats

1. Open Render Properties → Cycles → Device in Blender.
2. Check Display device memory stats (or Device Memory Stats in older 2.93‑series).
3. Render the scene. In the console you will see lines similar to:

   Cycles device memory: Geometry 128 MB, Textures 512 MB, BVH 64 MB, Shaders 32 MB

2. Verify the status‑bar total

After the render (or after a failure) look at the status bar’s Memory field. The number shown is the total VRAM the device claims to have used. Subtracting the geometry, BVH, and shader totals from this figure isolates the texture contribution.

3. Capture the peak with an external monitor

When a failure occurs before any tile finishes, Blender may not emit the per‑category breakdown. In that case use a GPU‑specific monitoring tool to record the maximum VRAM allocation during the attempt.

• NVIDIA: nvidia‑smi dmon -s u -i 0 1
• AMD: rocm‑smi --showmemuse
• Intel: intel_gpu_top

4. Disable automatic CPU fallback

In Render Properties → Performance → Feature Set, ensure Fallback to CPU is turned off. This guarantees that a VRAM OOM is reported by the GPU rather than silently switching to the CPU.

Procedure to capture peak per‑category VRAM usage

1. Enable device‑memory stats as described above.
2. Start an external monitor (e.g., nvidia‑smi dmon) before triggering the render.
3. Run the render. If it fails before a tile completes, stop the monitor and note the highest VRAM value reported.
4. After the render finishes or fails, read the console stats and status‑bar total. Verify that the sum of the categories matches the status‑bar figure; any discrepancy is likely due to temporary context overhead not shown by Blender.
5. Compare the external peak to the texture total from Blender. If the external peak is close to the texture total, textures are the main pressure point; if it is close to the geometry/BVH total, those are the culprits.

What we still need to know

Does the allocation failure occur before the first tile finishes, or after some tiles have been processed? This detail determines whether Blender’s per‑category stats will be present or whether you must rely on external monitoring.