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From:   Roman Gushchin <roman.gushchin@linux.dev>
To:     Tejun Heo <tj@kernel.org>
Cc:     Vasily Averin <vvs@openvz.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-kernel@vger.kernel.org, kernel@openvz.org,
        Shakeel Butt <shakeelb@google.com>,
        Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny@suse.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Michal Hocko <mhocko@suse.com>,
        Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH 0/3] enable memcg accounting for kernfs objects
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On Tue, Aug 09, 2022 at 07:31:31AM -1000, Tejun Heo wrote:
> (cc'ing Johannes)
> 
> Hello,
> 
> On Sun, Jul 31, 2022 at 06:37:15PM +0300, Vasily Averin wrote:
> > 1) creating a new netdevice allocates ~50Kb of memory, where ~10Kb
> >    was allocated for 80+ kernfs nodes.
> > 
> > 2) cgroupv2 mkdir allocates ~60Kb of memory, ~10Kb of them are kernfs
> >    structures.
> > 
> > 3) Shakeel Butt reports that Google has workloads which create 100s
> >    of subcontainers and they have observed high system overhead
> >    without memcg accounting of kernfs.
> 
> So, I don't have anything against accounting kernfs objects in general but,
> for cgroups, because cgroups are what determines what gets charged where,
> I'm not quite sure whether following the usual "charge it to the allocating
> task's cgroup" is the best way to go about it. I wonder whether it'd be
> better to attach it to the new cgroup's nearest ancestor with memcg enabled.

I also like this approach better, however Michal had some arguments against it.
I don't think there is a huge practical difference, so I'm ok with either
approach.

Thanks!