I've bisected systemd and found the commit that triggers the bug. http://bazaar.launchpad.net/~thopiekar/systemd/systemd-packaging-ubuntu- wily/revision/1706 seems to be the one. The commit is a bugfix that effectively enables hotadd for Xen. That can explain why more or less only Ubuntu 15.10 is affected, but the underlying mechanism is in the kernel.
A working workaround on the latest 15.10 is to comment out line 2 (ATTR{[dmi/id]sys_vendor}=="Xen", GOTO="vm_hotadd_apply") in /lib/udev/rules.d/40-vm-hotadd.rules -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1518457 Title: kswapd0 100% CPU usage To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1518457/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs