im using orangepi pc with ubuntu mate.
i've been watching the process kswapd0 is always using 99-100% of cpu and causing overheating (70-75degree).
even saw that there is no swap partition on my sd.
this is a kernel bug. but on Armbian (http://www.armbian.com/logbook/) with kernel 3.4112 it was fixed. Try Armbian and install armbianmonitor to see that it is fixed.