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I tried to render my scene with the new 2.79 Denoiser.

During the Rendering Process everything was fine, my memory peak was about 1000M but as soon as the Denoising started it suddenly shot up to ~2000M and gave me the "Out of memory in CuMemAlloc[...]" error.

Is Denoising usually taking up so much memory and why?

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Yes, memory usage increases substantially when Denoising.

Denoising needs the information of all of the adjacent rendered tiles to work, meaning that for every tile being rendered blender will keep in RAM the information of all the surrounding tiles, and will release that ram only when all surrounding tiles have been denoised.

As an example: to denoise tile 1, the denoiser needs the information from tiles 2 through 9.

enter image description here

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Like Cegaton said, it uses the other tiles in the memory. Using that logic, I ran a test, and found that if you reduce the tile size (in the performance pulldown) the image renders using much less. My file was usually around 1.3GB when rendering, but as soon as the denoise kicked in, it shot to 9GB, but I reduced tile size from 512 to 256, and now, the entire image rendered with denoising maxing at only 1.7GB.

So if it crashes, just remember that you can reduce the tilesize, and you should be fine.

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  • $\begingroup$ That makes sense: the amount of memory is fixed and limited, you would need to use smaller chunks in order to render using the existing resources. $\endgroup$ – cegaton Apr 13 '18 at 5:30
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    $\begingroup$ You can also try changing the tile order to one of the linear patterns (such as left-to-right or top-to-bottom) instead of "center" or "hilbert spiral". The linear pattern will reduce the number of waiting tiles by rendering in continuous strips. Left-to-right/right-to-left will be more efficient for landscape-orientation images since it reduces the length of the strip. Same for top-to-bottom or bottom-to-top with portrait-orientation images. $\endgroup$ – JtheNinja Apr 13 '18 at 6:15

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