From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with SMTP id 6F23B6B007B for ; Tue, 16 Feb 2010 18:45:43 -0500 (EST) Received: from m6.gw.fujitsu.co.jp ([10.0.50.76]) by fgwmail6.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id o1GNkA9N006016 for (envelope-from kamezawa.hiroyu@jp.fujitsu.com); Wed, 17 Feb 2010 08:46:10 +0900 Received: from smail (m6 [127.0.0.1]) by outgoing.m6.gw.fujitsu.co.jp (Postfix) with ESMTP id A075845DE52 for ; Wed, 17 Feb 2010 08:46:09 +0900 (JST) Received: from s6.gw.fujitsu.co.jp (s6.gw.fujitsu.co.jp [10.0.50.96]) by m6.gw.fujitsu.co.jp (Postfix) with ESMTP id 7537D45DE4C for ; Wed, 17 Feb 2010 08:46:09 +0900 (JST) Received: from s6.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s6.gw.fujitsu.co.jp (Postfix) with ESMTP id 5269C1DB8040 for ; Wed, 17 Feb 2010 08:46:09 +0900 (JST) Received: from m105.s.css.fujitsu.com (m105.s.css.fujitsu.com [10.249.87.105]) by s6.gw.fujitsu.co.jp (Postfix) with ESMTP id E030D1DB803A for ; Wed, 17 Feb 2010 08:46:08 +0900 (JST) Date: Wed, 17 Feb 2010 08:42:39 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [patch -mm 4/9 v2] oom: remove compulsory panic_on_oom mode Message-Id: <20100217084239.265c65ea.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: References: <20100216090005.f362f869.kamezawa.hiroyu@jp.fujitsu.com> <20100216092311.86bceb0c.kamezawa.hiroyu@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: David Rientjes Cc: Andrew Morton , Rik van Riel , Nick Piggin , Andrea Arcangeli , Balbir Singh , Lubos Lunak , KOSAKI Motohiro , linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Tue, 16 Feb 2010 01:02:28 -0800 (PST) David Rientjes wrote: > On Tue, 16 Feb 2010, KAMEZAWA Hiroyuki wrote: > > > > You don't understand that the behavior has changed ever since > > > mempolicy-constrained oom conditions are now affected by a compulsory > > > panic_on_oom mode, please see the patch description. It's absolutely > > > insane for a single sysctl mode to panic the machine anytime a cpuset or > > > mempolicy runs out of memory and is more prone to user error from setting > > > it without fully understanding the ramifications than any use it will ever > > > do. The kernel already provides a mechanism for doing this, OOM_DISABLE. > > > if you want your cpuset or mempolicy to risk panicking the machine, set > > > all tasks that share its mems or nodes, respectively, to OOM_DISABLE. > > > This is no different from the memory controller being immune to such > > > panic_on_oom conditions, stop believing that it is the only mechanism used > > > in the kernel to do memory isolation. > > > > > You don't explain why "we _have to_ remove API which is used" > > > > First, I'm not stating that we _have_ to remove anything, this is a patch > proposal that is open for review. > > Second, I believe we _should_ remove panic_on_oom == 2 because it's no > longer being used as it was documented: as we've increased the exposure of > the oom killer (memory controller, pagefault ooms, now mempolicy tasklist > scanning), we constantly have to re-evaluate the semantics of this option > while a well-understood tunable with a long history, OOM_DISABLE, already > does the equivalent. The downside of getting this wrong is that the > machine panics when it shouldn't have because of an unintended consequence > of the mode being enabled (a mempolicy ooms, for example, that was created > by the user). When reconsidering its semantics, I'd personally opt on the > safe side and make sure the machine doesn't panic unnecessarily and > instead require users to use OOM_DISABLE for tasks they do not want to be > oom killed. > Please don't. I had a chance to talk with customer support team and talked about panic_on_oom briefly. I understood that panic_on_oom_alyways+kdump is the strongest tool for investigating customer's OOM situtation and do the best advice to them. panic_on_oom_always+kdump is the 100% information as snapshot when oom-killer happens. Then, it's easy to investigate and explain what is wront. They sometimes discover memory leak (by some prorietary driver) or miss-configuration of the system (as using unnecessary bounce buffer.) Then, please leave panic_on_oom=always. Even with mempolicy or cpuset 's OOM, we need panic_on_oom=always option. And yes, I'll add something similar to memcg. freeze_at_oom or something. Thanks, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org