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From:   Shakeel Butt <shakeelb@google.com>
Date:   Mon, 28 Jan 2019 07:59:33 -0800
Message-ID: <CALvZod6LFY+FYfBcAX0kLxV5KKB1-TX2cU5EDyyyjvHOtuWWbA@mail.gmail.com>
Subject: Re: [PATCH 2/2] mm: Consider subtrees in memory.events
To:     Tejun Heo <tj@kernel.org>
Cc:     Michal Hocko <mhocko@kernel.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Chris Down <chris@chrisdown.name>,
        Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <guro@fb.com>, Dennis Zhou <dennis@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Cgroups <cgroups@vger.kernel.org>, Linux MM <linux-mm@kvack.org>,
        kernel-team@fb.com
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Hi Tejun,

On Fri, Jan 25, 2019 at 10:28 AM Tejun Heo <tj@kernel.org> wrote:
>
> Hello, Michal.
>
> On Fri, Jan 25, 2019 at 06:37:13PM +0100, Michal Hocko wrote:
> > > What if a user wants to monitor any ooms in the subtree tho, which is
> > > a valid use case?
> >
> > How is that information useful without know which memcg the oom applies
> > to?
>
> For example, a workload manager watching over a subtree for a job with
> nested memory limits set by the job itself.  It wants to take action
> (reporting and possibly other remediative actions) when something goes
> wrong in the delegated subtree but isn't involved in how the subtree
> is configured inside.
>

Why not make this configurable at the delegation boundary? As you
mentioned, there are jobs who want centralized workload manager to
watch over their subtrees while there can be jobs which want to
monitor their subtree themselves. For example I can have a job which
know how to act when one of the children cgroup goes OOM. However if
the root of that job goes OOM then the centralized workload manager
should do something about it. With this change, how to implement this
scenario? How will the central manager differentiates between that a
subtree of a job goes OOM or the root of that job? I guess from the
discussion it seems like the centralized manager has to traverse that
job's subtree to find the source of OOM.

Why can't we let the implementation of centralized manager easier by
allowing to configure the propagation of these notifications across
delegation boundary.

thanks,
Shakeel