The author of the blog post here.

In hindsight, the kernel bug seems obvious, but the process of tracking it down was quite interesting. I especially enjoyed the statistical analysis part, which isn't something you normally get to do while debugging :)

Anyway, I'd be happy to answer any questions you might have.

we recently ran into trouble where PGroonga on the other hand needs overcommit enabled, in direct opposition to postgres preferences: https://pgroonga.github.io/how-to/tuning.html