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

[alexhoppus]

(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.