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

2017-05-11 Thread Lennart Poettering 
On Thu, 11.05.17 10:26, Umut Tezduyar Lindskog (u...@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
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Re: [systemd-devel] 11 MB cost of DefaultMemoryAccounting=yes

2017-05-11 Thread Kai Krakow 
Am Thu, 11 May 2017 10:26:33 +0200
schrieb Umut Tezduyar Lindskog :

> Hello,
> 
> 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?

I think this is documented in the kernel as far as I know: Memory
accounting needs some extra memory. For swap accounting, it is even
more.

If you look at the kernel documentation: Does this explain your issue?

-- 
Regards,
Kai

Replies to list-only preferred.

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