[kwlug-disc] systemd and cgroup memory limits

[Chris Frey]

I'm hoping that someone here has managed to make this work.  So far, it's
been a maze of a twisty little passages, all alike. :-)

I played around with cgroups v1 before, and got it to work great.
But then systemd interfered and moved my processes into the user slice
without me asking.  I didn't track down the ultimate reason for that,
but I figured, fine, perhaps there is an official systemd way to do
this instead of using the cg* commands manually.

Here's what I have kinda working so far:

I create limittest.slice in /etc/systemd/system containing:

	[Slice]
	CPUQuota=10%
	MemoryAccounting=yes
	MemoryHigh=40M
	MemoryMax=80M
	MemorySwapMax=20M

The idea being that by the time 20M of swap + 80M of memory are used, it
will trigger OOM.

Then I run a shell:

	systemd-run --slice=limittest.slice --uid=cdfrey --shell

Then I run my test program to allocate and write to memory.

But OOM is never called.  MemoryMax does limit the memory to 80M and
all further allocations go to swap.  If I write to the memory I've
allocated, it dutifully churns through swap to do it.  So that's working.

But how do I stop it at 100M max?  I'd be happy with OOM killer for now,
but I really like cgroup v1's control over OOM behaviour, so I'm hoping
I can achieve that too.

Thanks!
- Chris