Re: [PATCH] ring-buffer: Add set/clear_current_oom_origin() during allocations

[Joel Fernandes]

On Thu, Apr 5, 2018 at 7:51 AM, Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> On Wed 04-04-18 16:59:18, Joel Fernandes wrote:
>> Hi Steve,
>>
>> On Wed, Apr 4, 2018 at 9:18 AM, Joel Fernandes <joelaf@xxxxxxxxxx> wrote:
>> > On Wed, Apr 4, 2018 at 9:13 AM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>> > [..]
>> >>>
>> >>> Also, I agree with the new patch and its nice idea to do that.
>> >>
>> >> Thanks, want to give it a test too?
>>
>> With the latest tree and the below diff, I can still OOM-kill a victim
>> process doing a large buffer_size_kb write:
>>
>> I pulled your ftrace/core and added this:
>> +       /*
>>         i = si_mem_available();
>>         if (i < nr_pages)
>>                 return -ENOMEM;
>> +       */
>>
>> Here's a run in Qemu with 4-cores 1GB total memory:
>>
>> bash-4.3# ./m -m 1M &
>> [1] 1056
>> bash-4.3#
>> bash-4.3#
>> bash-4.3#
>> bash-4.3# echo 10000000 > /d/tracing/buffer_size_kb
>> [   33.213988] Out of memory: Kill process 1042 (bash) score
>> 1712050900 or sacrifice child
>> [   33.215349] Killed process 1056 (m) total-vm:9220kB,
>> anon-rss:7564kB, file-rss:4kB, shmem-rss:640kB
>
> OK, so the reason your memory hog is triggered is that your echo is
> built-in and we properly select bask as an oom_origin but then another
> clever heuristic jumps in and tries to reduce the damage by sacrificing
> a child process. And your memory hog runs as a child from the same bash
> session.

Oh, ok. Makes sense.

>
> I cannot say I would love this heuristic. In fact I would really love to
> dig it deep under the ground. But this is a harder sell than it might
> seem. Anyway is your testing scenario really representative enough to

No honestly I don't care much for this heuristic but was just helping
test it. The scenario is not something I care about, but it seems like
if I hit it then others users will too. Maybe Zhaoyang can try his use
case again with ftrace/core and si_mem_available commented?

IOW I was just helping test the new patch with the si_mem_available
check commented out.

> care? Does the buffer_size_kb updater runs in the same process as any
> large memory process?

In this Qemu run its just the cat process. At work I use trace-cmd or
atrace neither of which I believe have large memory footprints (AFAIK)

Thanks,

- Joel