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From:   Shakeel Butt <shakeelb@google.com>
Date:   Mon, 17 Aug 2020 09:44:42 -0700
Message-ID: <CALvZod5V3N3K9-tDoaq=JgkeuAK=0TkRf97Vua0khXL+Lxw+Pg@mail.gmail.com>
Subject: Re: [RFC PATCH 1/8] memcg: Enable fine-grained control of over
 memory.high action
To:     Waiman Long <longman@redhat.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        LKML <linux-kernel@vger.kernel.org>, linux-doc@vger.kernel.org,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Cgroups <cgroups@vger.kernel.org>, Linux MM <linux-mm@kvack.org>
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On Mon, Aug 17, 2020 at 7:11 AM Waiman Long <longman@redhat.com> wrote:
>
> Memory controller can be used to control and limit the amount of
> physical memory used by a task. When a limit is set in "memory.high"
> in a non-root memory cgroup, the memory controller will try to reclaim
> memory if the limit has been exceeded. Normally, that will be enough
> to keep the physical memory consumption of tasks in the memory cgroup
> to be around or below the "memory.high" limit.
>
> Sometimes, memory reclaim may not be able to recover memory in a rate
> that can catch up to the physical memory allocation rate especially
> when rotating disks are used for swapping or writing dirty pages. In
> this case, the physical memory consumption will keep on increasing.

Isn't this the real underlying issue? Why not make the guarantees of
memory.high more strict instead of adding more interfaces and
complexity?

By the way, have you observed this issue on real workloads or some
test cases? It would be good to get a repro with simple test cases.