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Comment by sbuttgereit | Hacker News Reader

Wasn't there a Debian/Ubuntu thing recently where vm.swappiness = 0 had a behavior change which increased the number of incidents of the OOM killer stomping on things like database processes?

(Maybe it wasn't so new... https://www.percona.com/blog/2014/04/28/oom-relation-vm-swap...)

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Thank you for sharing this. There's an interesting conversation thread in the comments on that post. It's a little over my head, but my takeaway is that with the kernel change, in an OOM event, MySQL is unable to be swapped out due to the type(s) of memory pages it's using, so the kernel is forced to kill it (or itself). In practice, it's relatively straightforward to tune MySQL/MariaDB for a certain memory allocation, and if it's on a shared host, oom_score_adj can be set to protect it.

Can you not protect processes from the oomkiller? This is trivial and very useful on FreeBSD

https://www.freebsd.org/cgi/man.cgi?query=protect&sektion=1

Yes, with oom_score_adj[0], which I've mentioned several times. Setting it to -1000 for a process protects it from OOM killing.

0. http://man7.org/linux/man-pages/man5/proc.5.html

that looks painful to use. Do Linux distros let you automatically protect services? E.g. On FreeBSD:

mysql_enable="YES" mysql_oomprotect="YES"

Now every time you start the MySQL service it's automatically protected

Define "automatically" and "services" first ;-) Normally you just set it in the systemd's unit file for each daemon you want to adjust. So for some definitions of the above the answer is yes. (OOMScoreAdjust in https://www.freedesktop.org/software/systemd/man/systemd.exe...)

Personally, I use one tool for both FreeBSD and Linux. Picking up the (imported) rc.conf variable for a service is a mere matter of

    oom-kill-protect fromenv

And the conversion from something like OOMScoreAdjust is quite straightforward. A PostgreSQL systemd unit file that read OOMScoreAdjust=-625 becomes a run program that contains

    oom-kill-protect -- -625

* http://marc.info/?l=freebsd-hackers&m=145425153624976&w=2

* http://jdebp.eu./Softwares/nosh/guide/oom-kill-protect.html

Cool, thanks for sharing. I would hate to have to muck around in /proc manually to set this.

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