Bug#931111: linux-image-4.9.0-9: Memory "leak" caused by CGroup as used by pam_systemd
Hello Ben,
Am 24.07.19 um 00:03 schrieb Ben Hutchings:
> On Tue, 2019-07-23 at 15:56 +0200, Philipp Hahn wrote:
> [...]
>> - when the job / session terminates, the directory is deleted by
>> pam_systemd.
>>
>> - but the Linux kernel still uses the CGroup to track kernel internal
>> memory (SLAB objects, pending cache pages, ...?)
>>
>> - inside the kernel the CGroup is marked as "dying", but it is only
>> garbage collected very later on
> [...]
>> I do not know who is at fault here, if it is
>> - the Linux kernel for not freeing those resources earlier
>> - systemd for using CGs in a broken way
>> - someone others fault.
> [...]
>
> I would say this is a kernel bug. I think it's the same problem that
> this patch series is trying to solve:
> https://lwn.net/ml/linux-kernel/20190611231813.3148843-1-guro@fb.com/
>
> Does the description there seem to match what you're seeing?
Yes, Roman Gushchin replied to me by private mail, which I will quote
here to get his response archived in Debian's BTS as well:
> Hi Philipp!
>
> Thank you for the report!
>
> I've spent lot of time working on this problem, and the final patchset
> has been merged into 5.3. It implements reparenting of the slab memory
> on cgroup deletion. 5.3 should be much better in reclaiming dying cgroups.
>
> Unfortunately, the patchset is quite invasive and is based on some
> vmstats changes from 5.2, so it's not trivial to backport it to
> older kernels.
>
> Also, there is no good workaround, only manually dropping kernel
> caches or disable the kernel memory accounting as a whole.
>
> Thanks!
段熊春 <duanxiongchun@bytedance.com> also replied and pointed out his
patch-set <https://patchwork.kernel.org/cover/10772277/>, which solved
the problem for them. I more looks like a "hack", was never applied
upstream as Romans work solved the underlying problem.
So should someone™ bite the bullet and try to backport Romans change to
4.19 (and 4.9)? (those are the kernel versions used by Debian).
I'm not a kernel expert myself, especially no mm/cg expert, but have
done some work myself in the past, but I would happily pass on the
chalice to someone more experienced.
Thanks for all your replies - I really appreciate your help.
Philipp
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