I also opened a bug report for Mesa (https://bugs.freedesktop.org/show_bug.cgi?id=109958) as the glxgears problem occurs on different distributions, not just (K)ubuntu.
** Bug watch added: freedesktop.org Bugzilla #109958 https://bugs.freedesktop.org/show_bug.cgi?id=109958 -- You received this bug notification because you are a member of Ubuntu-X, which is subscribed to xorg-server in Ubuntu. https://bugs.launchpad.net/bugs/1815693 Title: Kubuntu 18.10 Xorg severe memory leak To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xorg-server/+bug/1815693/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~ubuntu-x-swat Post to : ubuntu-x-swat@lists.launchpad.net Unsubscribe : https://launchpad.net/~ubuntu-x-swat More help : https://help.launchpad.net/ListHelp
