Your system information

• Steam client version (build number or date):
• Distribution (e.g. Ubuntu): Kubuntu 18.04
• Opted into Steam client beta?: No
• Have you checked for system updates?: Yes

Please describe your issue in as much detail as possible:

A long session of gaming causes the amount of memory Xorg consumes to rise a lot. This is a pretty big issue, as in one hour Xorg may consume up to 200MB of RAM (from the usual 34MB), and games start stuttering, missing input or just causing a general drop in performance.
When closing steam Xorg almost instantly returns to nominal RAM usage, however this is also causing a system-wide freeze for a short period of time.

Steps for reproducing this issue:

1. Play games
2. Check the Xorg memory usage
3. Close steam
4. Check the Xorg memory usage again, note the drop of amount of memory allocated to the process.