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=-3.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 ABD19C2D0A3 for ; Mon, 9 Nov 2020 16:06:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4B65E206CB for ; Mon, 9 Nov 2020 16:06:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="Xrr1q1Kp" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730002AbgKIQGV (ORCPT ); Mon, 9 Nov 2020 11:06:21 -0500 Received: from mx2.suse.de ([195.135.220.15]:41144 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727774AbgKIQGV (ORCPT ); Mon, 9 Nov 2020 11:06:21 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1604937979; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=8X96c2/H5wzDkqogVwautXAUAzUmZ3oj3YSRgwu1wjs=; b=Xrr1q1Kpx83+bHS3BP0vuURiWs0c741Dw7MaSEVo3payss/4etcMOpUmKHXKNK1IoxwHFd da6YR6W4TLOeoWU9CunN7gQcvjwxGk4LSW+qa5+LF9frnqKrWUndLDO8CoOF056SmreTTd y71oU4G+FLtuiBEauZPkKQlAt8sxmR4= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 5744AAB93; Mon, 9 Nov 2020 16:06:19 +0000 (UTC) Date: Mon, 9 Nov 2020 17:06:18 +0100 From: Michal Hocko To: Minchan Kim Cc: Andrew Morton , LKML , linux-mm Subject: Re: [PATCH] mm: introduce oom_kill_disable sysctl knob Message-ID: <20201109160618.GI12240@dhcp22.suse.cz> References: <20201106203238.1375577-1-minchan@kernel.org> <20201109073706.GA12240@dhcp22.suse.cz> <20201109153933.GA449970@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201109153933.GA449970@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 09-11-20 07:39:33, Minchan Kim wrote: > On Mon, Nov 09, 2020 at 08:37:06AM +0100, Michal Hocko wrote: > > On Fri 06-11-20 12:32:38, Minchan Kim wrote: > > > It's hard to have some tests to be supposed to work under heavy > > > memory pressure(e.g., injecting some memory hogger) because > > > out-of-memory killer easily kicks out one of processes so system > > > is broken or system loses the memory pressure state since it has > > > plenty of free memory soon so. > > > > I do not follow the reasoning here. So you want to test for a close to > > no memory available situation and the oom killer stands in the way > > because it puts a relief? > > Yub, technically, I'd like to have consistent memory pressure to cause > direct reclaims on proesses on the system and swapping in/out. > > > > > Even though we could mark existing process's oom_adj to -1000, > > > it couldn't cover upcoming processes to be forked for the job. > > > > Why? > > Thing is the system has out-of-control processes created on demand. > so only option to prevent OOM is echo -1000 > `pidof the process` > since they are forked. However, I have no idea when they are forked > so should race with OOM with /proc polling and OOM is frequently > ahead of me. I am still confused. Why would you want all/most processes to be hidden from the oom killer? > > > This knob is handy to keep system memory pressure. > > > > This sounds like a very dubious reason to introduce a knob to cripple > > the system. > > > > I can see some reason to control the oom handling policy because the > > effect of the oom killer is really disruptive but a global on/off switch > > sounds like a too coarse interface. Really what kind of production > > environment would ever go with oom killer disabled completely? > > I don't think shipping production system will use it. It would be > just testing only option. Then it doesn't really belong to the kernel IMHO. > My intention uses such heavy memory load to see various system behaviors > before the production launching because it usually happens in real workload > once we shipped but hard to generate such a corner case without artificial > memory pressure. But changing the oom behavior will result in a completely different system behavior. So you would be testing something that doesn't really happen in any production system. > Any suggestion? Not really because I still do not understand your objective. You can generate memory pressure and tune it up for specific testing scenario. Sure there will be a some interference from the background noise (kernel subsystems reacting to external events, processes created etc.) but why that is a problem? This is normal to any running system. -- Michal Hocko SUSE Labs