Virtual Memory breakdown

I am having an out-of-memory problem. Target environment has 8GB main memory and 8GB VRAM (GeForce GTX 1080), but we can’t use paging file because target environment has no writable HDD. Therefore only 8GB of virtual memory can be used. When the problem occurs, “stat memoryplatform” command shows about 3GB of main memory and 7GB of virtual memory are used.

I’d like to know what this 4GB of difference stands for. I think that texture pool uses only virtual memory and explains a part of this 4GB, but the size of texture pool is set to less than 4GB. What other things may resident only in virtual memory?