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

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Message-ID: <CAGWkznGrugH0VqJyd5ZPiSBMOZ4SbbNpKiHVXM27Q-ep4SYb-Q@mail.gmail.com>
Date:   Tue, 10 Apr 2018 14:39:35 +0800
From:   Zhaoyang Huang <huangzhaoyang@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
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, Apr 10, 2018 at 2:14 PM, Michal Hocko <mhocko@...nel.org> wrote:
> 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
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)