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

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Date:   Tue, 21 Jul 2020 13:41:26 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     jingrui <jingrui@...wei.com>
Cc:     "tj@...nel.org" <tj@...nel.org>, Lizefan <lizefan@...wei.com>,
        "mhocko@...nel.org" <mhocko@...nel.org>,
        "vdavydov.dev@...il.com" <vdavydov.dev@...il.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        caihaomin <caihaomin@...wei.com>,
        "Weiwei (N)" <wick.wei@...wei.com>, guro@...xchg.org
Subject: Re: PROBLEM: cgroup cost too much memory when transfer small files
 to tmpfs

On Tue, Jul 21, 2020 at 11:19:52AM +0000, jingrui wrote:
> Cc: Johannes Weiner <hannes@...xchg.org> ; Michal Hocko <mhocko@...nel.org>; Vladimir Davydov <vdavydov.dev@...il.com>
> 
> 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.