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From:   Chunxin Zang <zangchunxin@bytedance.com>
Date:   Tue, 22 Sep 2020 18:24:35 +0800
Message-ID: <CAKRVAePisoOg8QBz11gPqzEoUdwPiJ-9Z9MyFE2LHzR-r+PseQ@mail.gmail.com>
Subject: Re: [External] Re: [PATCH] mm/memcontrol: Add the drop_cache
 interface for cgroup v2
To:     Chris Down <chris@chrisdown.name>
Cc:     Michal Hocko <mhocko@suse.com>, Yafang Shao <laoar.shao@gmail.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Tejun Heo <tj@kernel.org>, lizefan@huawei.com,
        Jonathan Corbet <corbet@lwn.net>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>, kafai@fb.com,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        andriin@fb.com, john.fastabend@gmail.com, kpsingh@chromium.org,
        Cgroups <cgroups@vger.kernel.org>, linux-doc@vger.kernel.org,
        Linux MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>, bpf@vger.kernel.org
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On Tue, Sep 22, 2020 at 5:51 PM Chris Down <chris@chrisdown.name> wrote:
>
> Chunxin Zang writes:
> >My usecase is that there are two types of services in one server. They
> >have difference
> >priorities. Type_A has the highest priority, we need to ensure it's
> >schedule latency=E3=80=81I/O
> >latency=E3=80=81memory enough. Type_B has the lowest priority, we expect=
 it
> >will not affect
> >Type_A when executed.
> >So Type_A could use memory without any limit. Type_B could use memory
> >only when the
> >memory is absolutely sufficient. But we cannot estimate how much
> >memory Type_B should
> >use. Because everything is dynamic. So we can't set Type_B's memory.high=
.
> >
> >So we want to release the memory of Type_B when global memory is
> >insufficient in order
> >to ensure the quality of service of Type_A . In the past, we used the
> >'force_empty' interface
> >of cgroup v1.
>
> This sounds like a perfect use case for memory.low on Type_A, and it's pr=
etty
> much exactly what we invented it for. What's the problem with that?

But we cannot estimate how much memory Type_A uses at least.
For example:
total memory: 100G
At the beginning, Type_A was in an idle state, and it only used 10G of memo=
ry.
The load is very low. We want to run Type_B to avoid wasting machine resour=
ces.
When Type_B runs for a while, it used 80G of memory.
At this time Type_A is busy, it needs more memory.

Usually we will reclaim the memory of B first for Type_A . If not
enough, we will
kill Type_B.