Cycles huge memory footprint

Dear all,
I’m trying to render a scene with hairs but every time I tried to render, I have a memory error.
So, Ok too much hairs… I’ve lowered until it renders but th number was too much low…so I started to investigate.

I’ve installed GPU-Z to check memory load and I’ve found something interesting (in a bad way).
If you take the default startup scene, add a plane a render it, the memory load grow from 300mb to 1100mb (in my computer) while blender said me in the viewport that the memory used is 32mb.

Is it just mine problem or someone could replicate it?

I’ve test both with nightly build and official 2.73a and they have the same behaviour.

My OS is win7 64bit and I have a GTX580 with 3Gb VRAM

Hello, try do render with CPU only. Gpu’s are often crashing because of memory error.

I would assume those 32 MB that Blender displays just refer to the memory footprint of that scene alone and not to the additional rendering infrastructure. In other words: 32 MB for that scene + about 1 GB for the CUDA render kernel.

Switch to the “Experimental” feature set for a moment and see what I mean: GPU-Z might now show even 2 GB of memory consumption for the very same scene, because the experimental kernel is much bigger than the standard one. Blender might as well still show the same 32 MB as before.

I think what we see here is the downside of adding more and more features to Cycles: The more feature-complete Cycles becomes, the more the render kernel will grow. I’ve read about Cycles users with 1.5 or even 2 GB cards that already start to have issues rendering even simple scenes.