From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753325AbcEMOXv (ORCPT ); Fri, 13 May 2016 10:23:51 -0400 Received: from smtpoutz299.laposte.net ([178.22.154.199]:37252 "EHLO smtp.laposte.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753128AbcEMOXu (ORCPT ); Fri, 13 May 2016 10:23:50 -0400 Message-ID: <5735E372.1090609@laposte.net> Date: Fri, 13 May 2016 16:23:46 +0200 From: Sebastian Frias User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 MIME-Version: 1.0 To: "Austin S. Hemmelgarn" , Michal Hocko CC: Mason , linux-mm@kvack.org, Andrew Morton , Linus Torvalds , LKML Subject: Re: [PATCH] mm: add config option to select the initial overcommit mode References: <5731CC6E.3080807@laposte.net> <20160513080458.GF20141@dhcp22.suse.cz> <573593EE.6010502@free.fr> <5735A3DE.9030100@laposte.net> <20160513120042.GK20141@dhcp22.suse.cz> <5735CAE5.5010104@laposte.net> <935da2a3-1fda-bc71-48a5-bb212db305de@gmail.com> <5735D7FC.3070409@laposte.net> In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-VR-SrcIP: 83.142.147.193 X-VR-FullState: 0 X-VR-Score: -100 X-VR-Cause-1: gggruggvucftvghtrhhoucdtuddrfeekledrvddugdejgecutefuodetggdotefrodftvfcurfhrohhf X-VR-Cause-2: ihhlvgemucfntefrqffuvffgnecuuegrihhlohhuthemucehtddtnecusecvtfgvtghiphhivghnthhs X-VR-Cause-3: ucdlqddutddtmdenucfjughrpefkfffhfgggvffufhgjtgfgsehtjegrtddtfeehnecuhfhrohhmpefu X-VR-Cause-4: vggsrghsthhirghnucfhrhhirghsuceoshhfkeegsehlrghpohhsthgvrdhnvghtqeenucfkphepkeef X-VR-Cause-5: rddugedvrddugeejrdduleefnecurfgrrhgrmhepmhhouggvpehsmhhtphhouhhtpdhhvghloheplgdu X-VR-Cause-6: jedvrddvjedrtddrvddugegnpdhinhgvthepkeefrddugedvrddugeejrdduleefpdhmrghilhhfrhho X-VR-Cause-7: mhepshhfkeegsehlrghpohhsthgvrdhnvghtpdhrtghpthhtoheprghhfhgvrhhrohhinhejsehgmhgr X-VR-Cause-8: ihhlrdgtohhm X-VR-AvState: No X-VR-State: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Austin, On 05/13/2016 04:14 PM, Austin S. Hemmelgarn wrote: > On 2016-05-13 09:34, Sebastian Frias wrote: >> Hi Austin, >> >> On 05/13/2016 03:11 PM, Austin S. Hemmelgarn wrote: >>> On 2016-05-13 08:39, Sebastian Frias wrote: >>>> >>>> My point is that it seems to be possible to deal with such conditions in a more controlled way, ie: a way that is less random and less abrupt. >>> There's an option for the OOM-killer to just kill the allocating task instead of using the scoring heuristic. This is about as deterministic as things can get though. >> >> By the way, why does it has to "kill" anything in that case? >> I mean, shouldn't it just tell the allocating task that there's not enough memory by letting malloc return NULL? > In theory, that's a great idea. In practice though, it only works if: > 1. The allocating task correctly handles malloc() (or whatever other function it uses) returning NULL, which a number of programs don't. > 2. The task actually has fallback options for memory limits. Many programs that do handle getting a NULL pointer from malloc() handle it by exiting anyway, so there's not as much value in this case. > 3. There isn't a memory leak somewhere on the system. Killing the allocating task doesn't help much if this is the case of course. Well, the thing is that the current behaviour, i.e.: overcommiting, does not improves the quality of those programs. I mean, what incentive do they have to properly handle situations 1, 2? Also, if there's a memory leak, the termination of any task, whether it is the allocating task or something random, does not help either, the system will eventually go down, right? > > You have to keep in mind though, that on a properly provisioned system, the only situations where the OOM killer should be invoked are when there's a memory leak, or when someone is intentionally trying to DoS the system through memory exhaustion. Exactly, the DoS attack is another reason why the OOM-killer does not seem a good idea, at least compared to just letting malloc return NULL and let the program fail. >If you're hitting the OOM killer for any other reason than those or a kernel bug, then you just need more memory or more swap space. > Indeed. Best regards, Sebastian