Why is the heap area constantly increasing when monitoring Tomcat using Java VisualVM?

Question

I have a JRubyOnRails application running on Tomcat. After viewing my application (localhost), logging in, and then doing nothing, the space with the heap seems to be continuously growing ...

This is normal? If I click on "Run GC", it will go down again. I am wondering what will happen if I leave it until it reaches my maximum computer memory?

And why is it growing all the time until nothing happens? Is it because I control my application?