[systemd-devel] Q: A way to log peak memory footprint of deactivating units?

[Michal Koutný]

Hello.

On Sat, Aug 13, 2022 at 04:39:50AM -0500, Russell Haley <yumpusamongus+systemd at gmail.com> wrote:
> Since systemd logs the total CPU time used when the unit deactivates, I
> wonder if there's a way to make it log the peak memory footprint too,
> kind of like the time command's "maxresident". The unit does have
> MemoryAccounting=yes.
> 
> It turned out that it was simple to write a shell script loop to wait
> until packagekit was activated and sample the memory usage before the
> timeout expired. (About 228 MiB.)  However, I am still interested to
> know if there might be a better/more general method.
> 
> P.S. Since I had to re-send this mail with the correct From: address, I
> looked into it and apparently kernel 5.19 added a memory.peak to cgroups
> v2, so I think it very recently become possible to have an elegant
> implementation of this.

You need the kernel with memory.peak (sampling is unrealiable) and then
quick n' dirty

> MemoryAccounting=yes
> ExecStopPost=/usr/bin/cat /sys/fs/cgroup/system.slice/%n/memory.peak

Output goes to journald by default:
> Aug 19 00:13:29 machine cat[7433]: 2924544

If you wanted to have this reported by default, PRs for memory.peak
support are welcomed :-)


Michal