Is it a well-known problem or some other? I don’t know. I rarely restart my computer at work. Why should I? There is one reason to restart all my stuff: X.
When I leave my computer running for a while, a few days or a week, X starts grabbing more and more memory. I managed to clean that up by loading a big “slow” page in firefox. But that is no solution because it is another problem.
I don’t consider restarting X a solution either. Is there a fix? Or is it not even X? Are there tools that clean up memory? Like calling a linux garbage collector ….. “please clean up now ….”