From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752327AbcEMOO7 (ORCPT ); Fri, 13 May 2016 10:14:59 -0400 Received: from mail-io0-f196.google.com ([209.85.223.196]:35789 "EHLO mail-io0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750862AbcEMOO6 (ORCPT ); Fri, 13 May 2016 10:14:58 -0400 Subject: Re: [PATCH] mm: add config option to select the initial overcommit mode To: Sebastian Frias , Michal Hocko 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> Cc: Mason , linux-mm@kvack.org, Andrew Morton , Linus Torvalds , LKML From: "Austin S. Hemmelgarn" Message-ID: Date: Fri, 13 May 2016 10:14:55 -0400 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.0 MIME-Version: 1.0 In-Reply-To: <5735D7FC.3070409@laposte.net> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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. 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.