From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752971AbbGJHld (ORCPT ); Fri, 10 Jul 2015 03:41:33 -0400 Received: from mail-wi0-f182.google.com ([209.85.212.182]:37478 "EHLO mail-wi0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752586AbbGJHl1 (ORCPT ); Fri, 10 Jul 2015 03:41:27 -0400 Date: Fri, 10 Jul 2015 09:41:24 +0200 From: Michal Hocko To: David Rientjes Cc: Andrew Morton , Jakob Unterwurzacher , linux-mm@kvack.org, LKML Subject: Re: [PATCH 1/4] oom: Do not panic when OOM killer is sysrq triggered Message-ID: <20150710074124.GB7343@dhcp22.suse.cz> References: <1436360661-31928-1-git-send-email-mhocko@suse.com> <1436360661-31928-2-git-send-email-mhocko@suse.com> <20150709082304.GA13872@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 09-07-15 14:03:53, David Rientjes wrote: > On Thu, 9 Jul 2015, Michal Hocko wrote: > > > > the titles were wrong for patches 2 and 3, but it doesn't mean we need to > > > add hacks around the code before organizing this into struct oom_control > > > > It is much easier to backport _fixes_ into older kernels (and yes I do > > care about that) if they do not depend on other cleanups. So I do not > > understand your point here. Besides that the cleanup really didn't make > > much change to the actuall fix because one way or another you still have > > to add a simple condition to rule out a heuristic/configuration which > > doesn't apply to sysrq+f path. > > > > So I am really lost in your argumentation here. > > > > This isn't a bugfix: sysrq+f has, at least for eight years, been able to > panic the kernel. This is an unwanted behavior and that is why I call it a bug. The mere fact that nobody has noticed because panic_on_oom is not used widely and even less with sysrq+f has nothing to do with it. > We're not fixing a bug, we're changing behavior. It's > quite appropriate to reorganize code before a behavior change to make it > cleaner. > > > > or completely pointless comments and printks that will fill the kernel > > > log. > > > > Could you explain what is so pointless about a comment which clarifies > > the fact which is not obviously visible from the current function? > > > > It states the obvious, a kthread is not going to be oom killed for > oom_kill_allocating_task: Sigh. The comment says that the force_kill path _runs_ from the kthread context which is far from obvious in out_of_memory. [...] > > Also could you explain why the admin shouldn't get an information if > > sysrq+f didn't kill anything because no eligible task has been found? > > The kernel log is the only notification mechanism that we have of the > kernel killing a process, we want to avoid spamming it unnecessarily. The > kernel log is not the appropriate place for your debugging information > that would only specify that yes, out_of_memory() was called, but there > was nothing actionable, especially when that trigger can be constantly > invoked by userspace once panicking is no longer possible. So how would you find out that there is no oom killable task? -- Michal Hocko SUSE Labs