linux-kernel - Re: [RFC PATCH] memcg: use root_mem

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Message-ID: <Ywd6hN1Q9MtQWZCp@cmpxchg.org>
Date:   Thu, 25 Aug 2022 09:35:00 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Zhaoyang Huang <huangzhaoyang@...il.com>
Cc:     Michal Hocko <mhocko@...e.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Tejun Heo <tj@...nel.org>, Shakeel Butt <shakeelb@...gle.com>,
        "zhaoyang.huang" <zhaoyang.huang@...soc.com>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Cgroups <cgroups@...r.kernel.org>, Ke Wang <ke.wang@...soc.com>,
        Zefan Li <lizefan.x@...edance.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Muchun Song <songmuchun@...edance.com>
Subject: Re: [RFC PATCH] memcg: use root_mem_cgroup when css is inherited

On Thu, Aug 25, 2022 at 06:11:09PM +0800, Zhaoyang Huang wrote:
> Sorry for any misunderstanding among the discussion. My purpose is
> real and simple as I have stated from the very beginning that I would
> like to have per-app cgroup hierarchy to charge memory to root if it
> is not enabled explicitly for memory. The reason has also been stated
> like reclaim and workingset regression in suren's report. I don't
> think my proposal will do any harm to current v2's mechanism besides
> asking for the admin echo "+memory" to their desire group.

It would permit children to escape parental control, completely
breaking the hierarchy and delegation guarantees currently in
place. That just isn't going to happen.

Nacked-by: Johannes Weiner <hannes@...xchg.org>

I would suggest focusing on finding the root cause for the reclaim
problem you are describing. It's possible all we need is a fix to
reclaim or the workingset code.