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=-1.0 required=3.0 tests=MAILING_LIST_MULTI autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by aws-us-west-2-korg-lkml-1.web.codeaurora.org (Postfix) with ESMTP id 890DEC004E4 for ; Wed, 13 Jun 2018 13:29:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 492592086A for ; Wed, 13 Jun 2018 13:29:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 492592086A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935556AbeFMN3s (ORCPT ); Wed, 13 Jun 2018 09:29:48 -0400 Received: from mx2.suse.de ([195.135.220.15]:44899 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935269AbeFMN3q (ORCPT ); Wed, 13 Jun 2018 09:29:46 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (charybdis-ext-too.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 38C2DAE2A; Wed, 13 Jun 2018 13:29:45 +0000 (UTC) Date: Wed, 13 Jun 2018 15:29:44 +0200 From: Michal Hocko To: Tetsuo Handa Cc: David Rientjes , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [rfc patch] mm, oom: fix unnecessary killing of additional processes Message-ID: <20180613132944.GL13364@dhcp22.suse.cz> References: <20180525072636.GE11881@dhcp22.suse.cz> <20180528081345.GD1517@dhcp22.suse.cz> <20180531063212.GF15278@dhcp22.suse.cz> <20180601074642.GW15278@dhcp22.suse.cz> <20180605085707.GV19202@dhcp22.suse.cz> <56138495-fd91-62f8-464a-db9960bfeb28@i-love.sakura.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56138495-fd91-62f8-464a-db9960bfeb28@i-love.sakura.ne.jp> User-Agent: Mutt/1.9.5 (2018-04-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 13-06-18 22:20:49, Tetsuo Handa wrote: > On 2018/06/05 17:57, Michal Hocko wrote: > >> For this reason, we see testing harnesses often oom killed immediately > >> after running a unittest that stresses reclaim or compaction by inducing a > >> system-wide oom condition. The harness spawns the unittest which spawns > >> an antagonist memory hog that is intended to be oom killed. When memory > >> is mlocked or there are a large number of threads faulting memory for the > >> antagonist, the unittest and the harness itself get oom killed because the > >> oom reaper sets MMF_OOM_SKIP; this ends up happening a lot on powerpc. > >> The memory hog has mm->mmap_sem readers queued ahead of a writer that is > >> doing mmap() so the oom reaper can't grab the sem quickly enough. > > > > How come the writer doesn't back off. mmap paths should be taking an > > exclusive mmap sem in killable sleep so it should back off. Or is the > > holder of the lock deep inside mmap path doing something else and not > > backing out with the exclusive lock held? > > > > Here is an example where the writer doesn't back off. > > http://lkml.kernel.org/r/20180607150546.1c7db21f70221008e14b8bb8@linux-foundation.org > > down_write_killable(&mm->mmap_sem) is nothing but increasing the possibility of > successfully back off. There is no guarantee that the owner of that exclusive > mmap sem will not be blocked by other unkillable waits. but we are talking about mmap() path here. Sure there are other paths which might need a back off while the lock is held and that should be addressed if possible but this is not really related to what David wrote above and I tried to understand. -- Michal Hocko SUSE Labs