linux-kernel - Re: [PATCH 1/1] mm, oom_adj: don't loop through tasks in __set_oom

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Message-ID: <20200820140054.fdkbotd4tgfrqpe6@wittgenstein>
Date:   Thu, 20 Aug 2020 16:00:54 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Michal Hocko <mhocko@...e.com>
Cc:     Suren Baghdasaryan <surenb@...gle.com>, timmurray@...gle.com,
        "Eric W. Biederman" <ebiederm@...ssion.com>, mingo@...nel.org,
        peterz@...radead.org, tglx@...utronix.de, esyr@...hat.com,
        christian@...lner.me, areber@...hat.com, shakeelb@...gle.com,
        cyphar@...har.com, oleg@...hat.com, adobriyan@...il.com,
        akpm@...ux-foundation.org, gladkov.alexey@...il.com,
        walken@...gle.com, daniel.m.jordan@...cle.com, avagin@...il.com,
        bernd.edlinger@...mail.de, john.johansen@...onical.com,
        laoar.shao@...il.com, minchan@...nel.org, kernel-team@...roid.com,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 1/1] mm, oom_adj: don't loop through tasks in
 __set_oom_adj when not necessary

On Thu, Aug 20, 2020 at 10:48:43PM +0900, Tetsuo Handa wrote:
> On 2020/08/20 22:34, Christian Brauner wrote:
> > On Thu, Aug 20, 2020 at 03:26:31PM +0200, Michal Hocko wrote:
> >> If you can handle vfork by other means then I am all for it. There were
> >> no patches in that regard proposed yet. Maybe it will turn out simpler
> >> then the heavy lifting we have to do in the oom specific code.
> > 
> > Eric's not wrong. I fiddled with this too this morning but since
> > oom_score_adj is fiddled with in a bunch of places this seemed way more
> > code churn then what's proposed here.
> 
> I prefer simply reverting commit 44a70adec910d692 ("mm, oom_adj: make sure
> processes sharing mm have same view of oom_score_adj").
> 
>   https://lore.kernel.org/patchwork/patch/1037208/

I guess this is a can of worms but just or the sake of getting more
background: the question seems to be whether the oom adj score is a
property of the task/thread-group or a property of the mm. I always
thought the oom score is a property of the task/thread-group and not the
mm which is also why it lives in struct signal_struct and not in struct
mm_struct. But

44a70adec910 ("mm, oom_adj: make sure processes sharing mm have same view of oom_score_adj")

reads like it is supposed to be a property of the mm or at least the
change makes it so.

Christian