From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933495AbcAMJkl (ORCPT ); Wed, 13 Jan 2016 04:40:41 -0500 Received: from mail-wm0-f51.google.com ([74.125.82.51]:36875 "EHLO mail-wm0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932526AbcAMJkg (ORCPT ); Wed, 13 Jan 2016 04:40:36 -0500 Date: Wed, 13 Jan 2016 10:40:34 +0100 From: Michal Hocko To: David Rientjes Cc: linux-mm@kvack.org, Tetsuo Handa , LKML Subject: Re: [RFC 3/3] oom: Do not try to sacrifice small children Message-ID: <20160113094034.GC28942@dhcp22.suse.cz> References: <1452632425-20191-1-git-send-email-mhocko@kernel.org> <1452632425-20191-4-git-send-email-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 12-01-16 16:51:43, David Rientjes wrote: > On Tue, 12 Jan 2016, Michal Hocko wrote: > > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > > index 8bca0b1e97f7..b5c0021c6462 100644 > > --- a/mm/oom_kill.c > > +++ b/mm/oom_kill.c > > @@ -721,8 +721,16 @@ try_to_sacrifice_child(struct oom_control *oc, struct task_struct *victim, > > if (!child_victim) > > goto out; > > > > - put_task_struct(victim); > > - victim = child_victim; > > + /* > > + * Protecting the parent makes sense only if killing the child > > + * would release at least some memory (at least 1MB). > > + */ > > + if (K(victim_points) >= 1024) { > > + put_task_struct(victim); > > + victim = child_victim; > > + } else { > > + put_task_struct(child_victim); > > + } > > > > out: > > return victim; > > The purpose of sacrificing a child has always been to prevent a process > that has been running with a substantial amount of work done from being > terminated and losing all that work if it can be avoided. This happens a > lot: imagine a long-living front end client forking a child which simply > collects stats and malloc information at a regular intervals and writes > them out to disk or over the network. These processes may be quite small, > and we're willing to happily sacrifice them if it will save the parent. > This was, and still is, the intent of the sacrifice in the first place. Yes I understand the intention of the heuristic. I am just contemplating about what is way too small to sacrifice because it clearly doesn't make much sense to kill a task which is sitting on basically no memory (well just few pages backing page tables and stack) because this would just prolong the OOM agony. > We must be able to deal with oom victims that are very small, since > userspace has complete control in prioritizing these processes in the > first place. Sure the patch is not great but I would like to come up with some threshold when children are way too small to be worthwhile considering. Or maybe there is other measure we can use. -- Michal Hocko SUSE Labs