linux-kernel - Re: [PATCH v1] ringbuffer: Don't choose the process with adj equal OOM_SCORE_ADJ

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Message-ID: <20180410081231.GV21835@dhcp22.suse.cz>
Date:   Tue, 10 Apr 2018 10:12:31 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Zhaoyang Huang <huangzhaoyang@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] ringbuffer: Don't choose the process with adj equal
 OOM_SCORE_ADJ_MIN

On Tue 10-04-18 16:04:40, Zhaoyang Huang wrote:
> On Tue, Apr 10, 2018 at 3:49 PM, Michal Hocko <mhocko@...nel.org> wrote:
> > On Tue 10-04-18 14:39:35, Zhaoyang Huang wrote:
> >> On Tue, Apr 10, 2018 at 2:14 PM, Michal Hocko <mhocko@...nel.org> wrote:
[...]
> >> > OOM_SCORE_ADJ_MIN means "hide the process from the OOM killer completely".
> >> > So what exactly do you want to achieve here? Because from the above it
> >> > sounds like opposite things. /me confused...
> >> >
> >> Steve's patch intend to have the process be OOM's victim when it
> >> over-allocating pages for ring buffer. I amend a patch over to protect
> >> process with OOM_SCORE_ADJ_MIN from doing so. Because it will make
> >> such process to be selected by current OOM's way of
> >> selecting.(consider OOM_FLAG_ORIGIN first before the adj)
> >
> > I just wouldn't really care unless there is an existing and reasonable
> > usecase for an application which updates the ring buffer size _and_ it
> > is OOM disabled at the same time.
> There is indeed such kind of test case on my android system, which is
> known as CTS and Monkey etc.

Does the test simulate a real workload? I mean we have two things here

oom disabled task and an updater of the ftrace ring buffer to a
potentially large size. The second can be completely isolated to a
different context, no? So why do they run in the single user process
context?

> Furthermore, I think we should make the
> patch to be as safest as possible. Why do we leave a potential risk
> here? There is no side effect for my patch.

I do not have the full context. Could you point me to your patch?
-- 
Michal Hocko
SUSE Labs