Motivation
When i upscale in background and my VRAM is fully used, i can't do sth video-like on forground (like watching a video). It's because of the VRAM, not GPU Usage.

Description
That's why it would be helpfull, if we could set a limit of how much can be used. For example if i have 12GB RAM, it would be nice, if the software (chainner) thinks, there is only 11GB. And then the rest 1GB is untouched for my system.

I know i could use tilesize, but auto-tile-size is for me a lot better, because otherwise i would have to test on each upscale, what tilesize is best. With this i just could use auto-tile-size but have still 1GB free.