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@xxxxxx/ > > 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@xxxxxxxxxxxxx> 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
