[systemd-devel] 11 MB cost of DefaultMemoryAccounting=yes

[Lennart Poettering]

On Thu, 11.05.17 10:26, Umut Tezduyar Lindskog (umut at tezduyar.com) wrote:

> Even though this is not a systemd problem, I believe systemd mailing
> list is a good place to discuss.
> 
> Our kernel has CONFIG_MEMCG enabled. As soon as we set
> DefaultMemoryAccounting=yes, our system wide memory usage increased 11
> MB. The increase is mostly on kmalloc-* slab memory with the peak on
> kmalloc-32.
> 
> I initially thought the increase is due to systemd creating
> system.slice under /sys/fs/cgroup/memory but I think I am wrong. I
> have run "systemd-run -p MemoryLimit=10M /bin/sleep 5" command while
> DefaultMemoryAccounting=no and there was no significant memory usage.
> 
> I am quite puzzled about where this extra cost is coming from. Does
> anybody have any idea?

cgroup memory accounting comes at a cost, both in performance and
memory usage. In older kernels it is so steep that many distros
disabled it altogether. On current kernels it shouldn't be awful
anymore, but like everything is not free...

I'd recommend talking to the memcg/cgroup community about this in more
detail.

Lennart

-- 
Lennart Poettering, Red Hat