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When I preview cycles render in viewport, the performance is solid and using 1 or 2GB memory. However when I render, at 128 samples, my pc freezes after about 2 seconds. Also, I have only got 16GB of ram, but the lower right corner says that the memory usage is 17.24GB. I render on the CPU, which is a Ryzen 2700x and I use blender 2.82. The scene is a desert render with an animated person walking. The desert has a subsurface material set to adaptive. There are only about 200.000 faces. Does anybody know what’s up with the ram and why my render freezes?

Thanks in advance

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  • $\begingroup$ Thank you for the fast reply. I will try that. $\endgroup$
    – Asmus Mortensen
    Jan 25, 2021 at 19:10
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    $\begingroup$ Hello :). Adaptive subdivision can send your 200 000 faces into tens of millions and easily take up 17 GB of memory. Tried that last week, my pc still hates me. $\endgroup$
    – jachym michal
    Jan 25, 2021 at 19:26

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Blender will use as much RAM as it needs to render the scene, until your system cannot provide those resources any more.

Usually, when the program needs more ram than installed on the hardware, the operating system will resort to "virtual memory", where the operating system will use a paging file (or "swap") on a hard drive to store the data that doesn fit in RAM anymore, not only slowing things down, but potentially crashing if the paging file is not large enough or gets currupted.

You have at least 4 choices:

Be patient and let the computer work, and crash and start over.

Or simplify/optimize the scene to match the limits of your hardware,

or add more memory to the system to meet your desired output,

or use a render farm or cloud computing.

As to why the specific scene you are trying to render is pushing the computer to the edge, there could be multiple explanations.

Subdividing can easily create a number of vertices that become unmanageable. The size of textures will have an impact on the resources available. Particles and simulations, deformations, moving armatures they also need heavy computing power, the number of samples, the size of the tiles, final render size, denoising and compositing will also need to RAM and CPU time. So start investigating how you can minimize/optimize the scene so that you can get something out of your computer.

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I assume your 200000 faces figure is after the subdivision. If so, this sounds like a similar issue to Cycles memory problem.

My understanding is that Cycles may use significantly more memory than necessary when doing a full render unless you tell it to use camera culling. This behavior is weird and I have no idea what is happening, but as the linked question's author said:

I cannot think of any logical reason, why a scene that uses 1GB VRAM in Cycles preview would use 10x as much in final rendering [...]

Enabling camera culling helped for me. Go to Render Properties > Simplify > Culling > enable Camera Culling, select all objects that should be culled, then go to Object Properties > Visibility > Culling > hold Alt and press Use Camera Cull. (Holding Alt means ticking the checkbox will be applied to all selected objects.)

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  • $\begingroup$ It was caused because of adaptive subdivision (since the camera might be too close and the dicing rate low for render), however, it's good that you answered since it might help others searching $\endgroup$
    – Yousuf Chaudhry
    Jul 5, 2022 at 18:20

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