Re: PROBLEM: cgroup cost too much memory when transfer small files to tmpfs

[Johannes Weiner]

On Tue, Jul 21, 2020 at 11:19:52AM +0000, jingrui wrote:
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> ; Michal Hocko <mhocko@xxxxxxxxxx>; Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
> 
> Thanks.
> 
> ---
> PROBLEM: cgroup cost too much memory when transfer small files to tmpfs.
> 
> keywords: cgroup PERCPU/memory cost too much.
> 
> description:
> 
> We send small files from node-A to node-B tmpfs /tmp directory using sftp. On
> node-B the systemd configured with pam on like below.
> 
> cat /etc/pam.d/password-auth | grep systemd
> -session     optional      pam_systemd.so
> 
> So when transfer a file, a systemd session is created, that means a cgroup is
> created, then file saved at /tmp will associated with a cgroup object. After
> file transferred, session and cgroup-dir will be removed, but the file in /tmp
> still associated with the cgroup object. The PERCPU memory in cgroup/css object
> cost a lot(about 0.5MB/per-cgroup-object) on 200/cpus machine.

CC Roman who had a patch series to free all this extended (percpu)
memory upon cgroup deletion:

https://lore.kernel.org/patchwork/cover/1050508/

It looks like it never got merged for some reason.