linux-kernel - Re: [RFC PATCH] memcg, oom: throttle dump_header for memcg ooms without eligible tasks

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Message-ID: <20181015112427.GI18839@dhcp22.suse.cz>
Date:   Mon, 15 Oct 2018 13:24:27 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
        syzkaller-bugs@...glegroups.com, guro@...com,
        kirill.shutemov@...ux.intel.com, linux-kernel@...r.kernel.org,
        rientjes@...gle.com, yang.s@...baba-inc.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC PATCH] memcg, oom: throttle dump_header for memcg ooms
 without eligible tasks

On Mon 15-10-18 19:57:35, Tetsuo Handa wrote:
> On 2018/10/15 17:19, Michal Hocko wrote:
> > As so many dozens of times before, I will point you to an incremental
> > nature of changes we really prefer in the mm land. We are also after a
> > simplicity which your proposal lacks in many aspects. You seem to ignore
> > that general approach and I have hard time to consider your NAK as a
> > relevant feedback. Going to an extreme and basing a complex solution on
> > it is not going to fly. No killable process should be a rare event which
> > requires a seriously misconfigured memcg to happen so wildly. If you can
> > trigger it with a normal user privileges then it would be a clear bug to
> > address rather than work around with printk throttling.
> > 
> 
> I can trigger 200+ times / 900+ lines / 69KB+ of needless OOM messages
> with a normal user privileges. This is a lot of needless noise/delay.

I am pretty sure you have understood the part of my message you have
chosen to not quote where I have said that the specific rate limitting
decisions can be changed based on reasonable configurations. There is
absolutely zero reason to NAK a natural decision to unify the throttling
and cook a per-memcg way for a very specific path instead.

> No killable process is not a rare event, even without root privileges.
>
> [root@...ecurity kumaneko]# time ./a.out
> Killed
> 
> real    0m2.396s
> user    0m0.000s
> sys     0m2.970s
> [root@...ecurity ~]# dmesg | grep 'no killable' | wc -l
> 202
> [root@...ecurity ~]# dmesg | wc
>     942    7335   70716

OK, so this is 70kB worth of data pushed throug the console. Is this
really killing any machine?
-- 
Michal Hocko
SUSE Labs