From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it1-f197.google.com (mail-it1-f197.google.com [209.85.166.197]) by kanga.kvack.org (Postfix) with ESMTP id D909C6B0007 for ; Mon, 15 Oct 2018 08:47:42 -0400 (EDT) Received: by mail-it1-f197.google.com with SMTP id e197-v6so21492507ita.9 for ; Mon, 15 Oct 2018 05:47:42 -0700 (PDT) Received: from www262.sakura.ne.jp (www262.sakura.ne.jp. [202.181.97.72]) by mx.google.com with ESMTPS id z21-v6si6400757ioh.128.2018.10.15.05.47.41 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 15 Oct 2018 05:47:41 -0700 (PDT) Subject: Re: [RFC PATCH] memcg, oom: throttle dump_header for memcg ooms without eligible tasks References: <20181012112008.GA27955@cmpxchg.org> <20181012120858.GX5873@dhcp22.suse.cz> <9174f087-3f6f-f0ed-6009-509d4436a47a@i-love.sakura.ne.jp> <20181012124137.GA29330@cmpxchg.org> <0417c888-d74e-b6ae-a8f0-234cbde03d38@i-love.sakura.ne.jp> <20181013112238.GA762@cmpxchg.org> <20181015081934.GD18839@dhcp22.suse.cz> <20181015112427.GI18839@dhcp22.suse.cz> From: Tetsuo Handa Message-ID: <6c0a57b3-bfd4-d832-b0bd-5dd3bcae460e@i-love.sakura.ne.jp> Date: Mon, 15 Oct 2018 21:47:08 +0900 MIME-Version: 1.0 In-Reply-To: <20181015112427.GI18839@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Johannes Weiner , linux-mm@kvack.org, syzkaller-bugs@googlegroups.com, guro@fb.com, kirill.shutemov@linux.intel.com, linux-kernel@vger.kernel.org, rientjes@google.com, yang.s@alibaba-inc.com, Andrew Morton , Sergey Senozhatsky , Petr Mladek , Sergey Senozhatsky , Steven Rostedt On 2018/10/15 20:24, Michal Hocko wrote: > 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@ccsecurity kumaneko]# time ./a.out >> Killed >> >> real 0m2.396s >> user 0m0.000s >> sys 0m2.970s >> [root@ccsecurity ~]# dmesg | grep 'no killable' | wc -l >> 202 >> [root@ccsecurity ~]# dmesg | wc >> 942 7335 70716 > > OK, so this is 70kB worth of data pushed throug the console. Is this > really killing any machine? > Nobody can prove that it never kills some machine. This is just one example result of one example stress tried in my environment. Since I am secure programming man from security subsystem, I really hate your "Can you trigger it?" resistance. Since this is OOM path where nobody tests, starting from being prepared for the worst case keeps things simple.