linux-kernel - Re: [RFC PATCH 1/8] memcg: Enable fine-grained control of over memory.high action

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Message-ID: <20200817143044.GA1987@chrisdown.name>
Date:   Mon, 17 Aug 2020 15:30:44 +0100
From:   Chris Down <chris@...isdown.name>
To:     Waiman Long <longman@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Jonathan Corbet <corbet@....net>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [RFC PATCH 1/8] memcg: Enable fine-grained control of over
 memory.high action

Astractly, I think this really overcomplicates the API a lot. If these are 
truly generally useful (and I think that remains to be demonstrated), they 
should be additions to the existing API, rather than a sidestep with prctl.

I also worry about some other more concrete things:

1. Doesn't this allow unprivileged applications to potentially bypass 
    memory.high constraints set by a system administrator?
2. What's the purpose of PR_MEMACT_KILL, compared to memory.max?
3. Why add this entirely separate signal delivery path when we already have 
    eventfd/poll/inotify support, which makes a lot more sense for modern 
    applications?