linux-kernel - Re: [PATCH 3/4] memcg: enable accounting for struct cgroup

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Message-ID: <740dfcb1-5c5f-6a40-0f71-65f277f976d6@openvz.org>
Date:   Fri, 20 May 2022 10:24:06 +0300
From:   Vasily Averin <vvs@...nvz.org>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>, kernel@...nvz.org,
        linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>, cgroups@...r.kernel.org
Subject: Re: [PATCH 3/4] memcg: enable accounting for struct cgroup

On 5/19/22 19:53, Michal Koutný wrote:
> On Fri, May 13, 2022 at 06:52:12PM +0300, Vasily Averin <vvs@...nvz.org> wrote:
>> Creating each new cgroup allocates 4Kb for struct cgroup. This is the
>> largest memory allocation in this scenario and is epecially important
>> for small VMs with 1-2 CPUs.
> 
> What do you mean by this argument?
> 
> (On bigger irons, the percpu components becomes dominant, e.g. struct
> cgroup_rstat_cpu.)

Michal, Shakeel,
thank you very much for your feedback, it helps me understand how to improve
the methodology of my accounting analyze.
I considered the general case and looked for places of maximum memory allocations.
Now I think it would be better to split all called allocations into:
- common part, called for any cgroup type (i.e. cgroup_mkdir and cgroup_create),
- per-cgroup parts,
and focus on 2 corner cases: for single CPU VMs and for "big irons".
It helps to clarify which allocations are accounting-important and which ones
can be safely ignored.

So right now I'm going to redo the calculations and hope it doesn't take long.

Thank you,
	Vasily Averin