From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f70.google.com (mail-wm0-f70.google.com [74.125.82.70]) by kanga.kvack.org (Postfix) with ESMTP id 2F0CE6B0005 for ; Fri, 13 May 2016 10:23:49 -0400 (EDT) Received: by mail-wm0-f70.google.com with SMTP id r12so10843549wme.0 for ; Fri, 13 May 2016 07:23:49 -0700 (PDT) Received: from smtp.laposte.net (smtpoutz25.laposte.net. [194.117.213.100]) by mx.google.com with ESMTPS id cl10si22472960wjc.19.2016.05.13.07.23.47 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 13 May 2016 07:23:47 -0700 (PDT) Received: from smtp.laposte.net (localhost [127.0.0.1]) by lpn-prd-vrout013 (Postfix) with ESMTP id 90D3C1046C3 for ; Fri, 13 May 2016 16:23:47 +0200 (CEST) Received: from lpn-prd-vrin002 (lpn-prd-vrin002.laposte [10.128.63.3]) by lpn-prd-vrout013 (Postfix) with ESMTP id 8F6331046CB for ; Fri, 13 May 2016 16:23:47 +0200 (CEST) Received: from lpn-prd-vrin002 (localhost [127.0.0.1]) by lpn-prd-vrin002 (Postfix) with ESMTP id 7A3DE5BF011 for ; Fri, 13 May 2016 16:23:47 +0200 (CEST) Message-ID: <5735E372.1090609@laposte.net> Date: Fri, 13 May 2016 16:23:46 +0200 From: Sebastian Frias MIME-Version: 1.0 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 Sender: owner-linux-mm@kvack.org List-ID: To: "Austin S. Hemmelgarn" , Michal Hocko Cc: Mason , linux-mm@kvack.org, Andrew Morton , Linus Torvalds , LKML 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 -- 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