Developertools for Gnome3 - memory management...

When you have troubles with the gnome-shell you can start the
command-prompt with the key-shortcut <Alt>-<F2> and type the
letter 'r', which restarts the shell.

I knew from long ago, that there is also something like a garbage collector
and now I've found a collection of tips here.

To get to the developer tools of gnome-shell get to the command prompt with <Alt>-<F2> and insert 'lg'.

In the appearing window you can switch over to the memory and issue a
FullGC