linux-kernel - Re: [PATCH v2 3/3] mm: memcontrol: recursive memory.low protection

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Message-ID: <20200217084100.GE31531@dhcp22.suse.cz>
Date:   Mon, 17 Feb 2020 09:41:00 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Tejun Heo <tj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH v2 3/3] mm: memcontrol: recursive memory.low protection

On Fri 14-02-20 11:53:11, Johannes Weiner wrote:
[...]
> The proper solution to implement the kind of resource hierarchy you
> want to express in cgroup2 is to reflect it in the cgroup tree. Yes,
> the_workload might have been started by user 100 in session c2, but in
> terms of resources, it's prioritized over system.slice and user.slice,
> and so that's the level where it needs to sit:
> 
>                                root
>                        /        |                 \
>                system.slice  user.slice       the_workload
>                /    |           |
>            cron  journal     user-100.slice
>                                 |
>                              session-c2.scope
>                                 |
>                              misc
> 
> Then you can configure not just memory.low, but also a proper io
> weight and a cpu weight. And the tree correctly reflects where the
> workload is in the pecking order of who gets access to resources.

I have already mentioned that this would be the only solution when the
protection would work, right. But I am also saying that this a trivial
example where you simply _can_ move your workload to the 1st level. What
about those that need to reflect organization into the hierarchy. Please
have a look at http://lkml.kernel.org/r/20200214075916.GM31689@dhcp22.suse.cz
Are you saying they are just not supported? Are they supposed to use
cgroup v1 for the organization and v2 for the resource control?
-- 
Michal Hocko
SUSE Labs