Hey Mikel,
I downloaded your scene, first thing I did was create the instances directly on points, the grid setup brings Houdini to its knees apparently. So I just added one point, and then used three copy and transform nodes to create a box of points, then set the instance attribute in a point wrangle " s@instance="/obj/Piggy/" ".
I'm rendering on a single GTX 1080 ti. Houdini 18.0.499 + Octane 2020.1.2
210x210x210 = 09 261 000 instances : memory (used/free): 4001/4917 MB : it renders and Houdini freezes when I try to close the IPR.
230x230x230 = 12 167 000 instances : memory (used/free): 5076/3781 MB : it renders and Houdini did not freeze when I closed the IPR. ( ? )
235x235x235 = 12 977 875 instances : memory (used/free): 5376/3778 MB : it renders and Houdini freezes when I try to close the IPR.
240x240x240 = 13 824 000 instances : CUDA error 2 on device 0: out of memory
250x250x250 = 15 625 000 instances : freeze/crash on preprocessing
Preprocessing took quite some time of course. It seems like something's going on with the memory usage or with the memory usage information that is being displayed.
I was curious so I did some tests with rendering the points as sphere particles:
300x300x300 = 27 000 000 particles : memory (used/free): 2806/5797 MB : it renders, IPR closed fine.
400x400x400 = 64 000 000 particles : memory (used/free): 5058/2940 MB : it renders, IPR still closed, not very responsive ( 64 Million particles though !! )
450x450x450 = 91 125 000 particles : freeze/crash on preprocessing.