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

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Date:   Tue, 10 Apr 2018 08:14:47 +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 11:41:44, Zhaoyang Huang wrote:
> On Tue, Apr 10, 2018 at 11:12 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
> > On Tue, 10 Apr 2018 10:32:36 +0800
> > Zhaoyang Huang <huangzhaoyang@...il.com> wrote:
> >
> >> For bellowing scenario, process A have no intension to exhaust the
> >> memory, but will be likely to be selected by OOM for we set
> >> OOM_CORE_ADJ_MIN for it.
> >> process A(-1000)                                          process B
> >>
> >>   i = si_mem_available();
> >>        if (i < nr_pages)
> >>            return -ENOMEM;
> >>                                                    schedule
> >>                                                 --------------->
> >> allocate huge memory
> >>                                                 <-------------
> >> if (user_thread)
> >>   set_current_oom_origin();
> >>
> >>   for (i = 0; i < nr_pages; i++) {
> >>          bpage = kzalloc_node
> >
> > Is this really an issue though?
> >
> > Seriously, do you think you will ever hit this?
> >
> > How often do you increase the size of the ftrace ring buffer? For this
> > to be an issue, the system has to trigger an OOM at the exact moment
> > you decide to increase the size of the ring buffer. That would be an
> > impressive attack, with little to gain.
> >
> > Ask the memory management people. If they think this could be a
> > problem, then I'll be happy to take your patch.
> >
> > -- Steve
> add Michael for review.
> Hi Michael,
> I would like suggest Steve NOT to set OOM_CORE_ADJ_MIN for the process
> with adj = -1000 when setting the user space process as potential
> victim of OOM.

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...

-- 
Michal Hocko
SUSE Labs