From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E90F4C3A5A1 for ; Wed, 28 Aug 2019 11:12:54 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 9BF2E2189D for ; Wed, 28 Aug 2019 11:12:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9BF2E2189D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 26F006B0008; Wed, 28 Aug 2019 07:12:54 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 21F6B6B000C; Wed, 28 Aug 2019 07:12:54 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1351F6B000D; Wed, 28 Aug 2019 07:12:54 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0108.hostedemail.com [216.40.44.108]) by kanga.kvack.org (Postfix) with ESMTP id E5B7F6B0008 for ; Wed, 28 Aug 2019 07:12:53 -0400 (EDT) Received: from smtpin07.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with SMTP id A6638610C for ; Wed, 28 Aug 2019 11:12:53 +0000 (UTC) X-FDA: 75871574226.07.crow09_70837d130e93f X-HE-Tag: crow09_70837d130e93f X-Filterd-Recvd-Size: 4067 Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) by imf32.hostedemail.com (Postfix) with ESMTP for ; Wed, 28 Aug 2019 11:12:53 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 622BEAF0B; Wed, 28 Aug 2019 11:12:49 +0000 (UTC) Date: Wed, 28 Aug 2019 13:12:48 +0200 From: Michal Hocko To: Tetsuo Handa Cc: Edward Chron , Qian Cai , Andrew Morton , Roman Gushchin , Johannes Weiner , David Rientjes , Shakeel Butt , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Ivan Delalande Subject: Re: [PATCH 00/10] OOM Debug print selection and additional information Message-ID: <20190828111248.GE28313@dhcp22.suse.cz> References: <1566909632.5576.14.camel@lca.pw> <79FC3DA1-47F0-4FFC-A92B-9A7EBCE3F15F@lca.pw> <2A1D8FFC-9E9E-4D86-9A0E-28F8263CC508@lca.pw> <20190828070845.GC7386@dhcp22.suse.cz> <2e816b05-7b5b-4bc0-8d38-8415daea920d@i-love.sakura.ne.jp> <20190828103211.GD28313@dhcp22.suse.cz> <5db2d2bd-645b-8967-849a-0d1de5861742@i-love.sakura.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5db2d2bd-645b-8967-849a-0d1de5861742@i-love.sakura.ne.jp> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed 28-08-19 19:56:58, Tetsuo Handa wrote: > On 2019/08/28 19:32, Michal Hocko wrote: > >> Speak of my cases, those who take care of their systems are not developers. > >> And they afraid changing code that runs in kernel mode. They unlikely give > >> permission to install SystemTap/eBPF scripts. As a result, in many cases, > >> the root cause cannot be identified. > > > > Which is something I would call a process problem more than a kernel > > one. Really if you need to debug a problem you really have to trust > > those who can debug that for you. We are not going to take tons of code > > to the kernel just because somebody is afraid to run a diagnostic. > > > > This is a problem of kernel development process. I disagree. Expecting that any larger project can be filled with the (close to) _full_ and ready to use introspection built in is just insane. We are trying to help with a generally useful information but you simply cannot cover most existing failure paths. > >> Moreover, we are talking about OOM situations, where we can't expect userspace > >> processes to work properly. We need to dump information we want, without > >> counting on userspace processes, before sending SIGKILL. > > > > Yes, this is an inherent assumption I was making and that means that > > whatever dynamic hooks would have to be registered in advance. > > > > No. I'm saying that neither static hooks nor dynamic hooks can work as > expected if they count on userspace processes. Registering in advance is > irrelevant. Whether it can work without userspace processes is relevant. I am not saying otherwise. I do not expect any userspace process to dump any information or read it from elswhere than from the kernel log. > Also, out-of-tree codes tend to become defunctional. We are trying to debug > problems caused by in-tree code. Breaking out-of-tree debugging code just > because in-tree code developers don't want to pay the burden of maintaining > code for debugging problems caused by in-tree code is a very bad idea. This is a simple math of cost/benefit. The maintenance cost is not free and paying it for odd cases most people do not care about is simply not sustainable, we simply do not have that much of a man power. -- Michal Hocko SUSE Labs