Comment by gf000

> but there's no way for a program to know how much memory is available

It usually knows the total system RAM available, and within containers it knows the resource limits. So your statement is false.

> And there is such a thing as "appropriate amount of memory for this task"

Appropriate for whom? Who to tell that I want this app to have better throughput and I don't care how much memory it would cost, or that I don't care about slightly lower throughput but I want the least amount of memory used?

> Now consider you'd be burdening every single user of the program with the above

Or you know, just set one as the developer? There is not even such a thing as a JRE anymore, the prevalent way to ship a Java app is with a "JRE" made up from only the modules that the app needs, started with a shell script or so. You can trivially set as a developer your own set of flags and parameters.