I know you think you're being facetious, but you've just described how modern operating systems work. They give programs a reasonable amount of memory, without

I know you think you're being facetious, but you've just described how modern operating systems work. They give programs a reasonable amount of memory, without getting into specifics about the limits. And they reclaim memory as necessary based on the demands of the OS and other programs. See, for example, browser memory usage vs video game usage. It turns out that in practice "reasonable" works quite well as long as you are reasonable about it.