Why there is no GPU swap support in linux based systems?

(The things below are mainly related to arm mali systems) Hi. Actually i want to know - why there is no GPU Swap support in Linux based systems? It seems that the GPU works with graphical contexts in the same fashion as CPU handle things. I mean there are page faults, GPU have its own MMU, the memory used by GPU devices allocated via trivial page_alloc mechanism. You would say that performance is a reason, but there are some swap backends like zram: they use in-memory compression instead of disk swapping. Moreover, i think there would be a GPU data which could be swapped without significant drawbacks, because it accessed very rare. Thank you.