I’ve been around awhile, and I still don’t understand this. Take 2.80 (the same happens in 2.79, but the UI change means I have to pick one). I have a scene, and I hit render (F12 - not viewport). At the bottom right of the render window is a memory usage guage, and also at the top left. Bottom right, when rendering, is a dynamic value. but maxes out at around 13Gb. Top right maxes out at around 5Gb.
Using hybrid rendering (GPU/CPU) my GPU has 6Gb, and so I don’t expect this to render (y’know, 13Gb) but it does.
from observation, the bottom right value appears to be reporting VRAM. I say this because as I increase the render size, this inches up. Top left, however, is relatively stable.
So, what are each? Have I got it wrong completely, and bottom right is scene memory (which I can handle) and top left is render memory, and if so, why does bottom right crank up whilst building BVH?