Comment # 16 on bug 1013629 from Vlastimil Babka

(In reply to Howard Guo from comment #14)
> Of course kswapd was using 100% CPU, consequently a simple cp and `sleep 1`
> together would take 2 seconds to complete, which is why the vmstat file
> timestamps aren't consecutive.

You could try perf sampling to see where kswapd spends the cpu:

perf record -a -g
(let it run for e.g. a minute, then ctrl^c
perf report -g

> Should I disable THP and monitor for its occurrence?