A lot of this has to do with the fact that texture
memory is counted as mapped in our process, even though
it's really on the dedicated GPU memory.
So, every pixel of every window is counted by being in our
process (and also in the X server), because it's part of our
address space, but they're all sharing the same actual
memory on the GPU.
It depends on the driver, of course, but Intel and NVIDIA has
this issue.
