It can go higher actually, just that when I setup my test devices I had a "ought to be enough for everyone" moment when typing `options amdgpu gttsize=110000`. I guess this number spread too far, heh.

See also:

[1] https://en.wikipedia.org/wiki/Graphics_address_remapping_tab...

[2] https://www.kernel.org/doc/html/v4.19/gpu/amdgpu.html#:~:tex...