Date:   Tue, 10 Apr 2018 17:51:14 +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 5:32 PM, Zhaoyang Huang <huangzhaoyang@...il.com> wrote:
> On Tue, Apr 10, 2018 at 5:01 PM, Michal Hocko <mhocko@...nel.org> wrote:
>> On Tue 10-04-18 16:38:32, Zhaoyang Huang wrote:
>>> On Tue, Apr 10, 2018 at 4:12 PM, Michal Hocko <mhocko@...nel.org> wrote:
>>> > 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?
>>> ok. I think there are some misunderstandings here. Let me try to
>>> explain more by my poor English. There is just one thing here. The
>>> updater is originally a oom disabled task with adj=OOM_SCORE_ADJ_MIN.
>>> With Steven's patch, it will periodically become a oom killable task
>>> by calling set_current_oom_origin() for user process which is
>>> enlarging the ring buffer. What I am doing here is limit the user
>>> process to the ones that adj > -1000.
>>
>> I've understood that part. And I am arguing whether this is really such
>> an important case to play further tricks. Wouldn't it be much simpler to
>> put the updater out to a separate process? OOM disabled processes
>> shouldn't really do unexpectedly large allocations. Full stop. Otherwise
>> you risk a large system disruptions.
>> --
> It is a real problem(my android system just hung there while running
> the test case for the innocent key process killed by OOM), however,
> the problem is we can not define the userspace's behavior as you
> suggested. What Steven's patch doing here is to keep the system to be
> stable by having the updater to take the responsbility itself. My
> patch is to let the OOM disabled processes remain the unkillable
> status.
>
>> Michal Hocko
>> SUSE Labs
To summarize the patch sets as 'let the updater take the
responsibility itself, don't harm to the innocent, but absolve the
critical process'

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