From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754675AbYBEEPo (ORCPT ); Mon, 4 Feb 2008 23:15:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752566AbYBEEPg (ORCPT ); Mon, 4 Feb 2008 23:15:36 -0500 Received: from E23SMTP06.au.ibm.com ([202.81.18.175]:43737 "EHLO e23smtp06.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750940AbYBEEPf (ORCPT ); Mon, 4 Feb 2008 23:15:35 -0500 Message-ID: <47A7E282.1080902@linux.vnet.ibm.com> Date: Tue, 05 Feb 2008 09:43:54 +0530 From: Balbir Singh Reply-To: balbir@linux.vnet.ibm.com Organization: IBM User-Agent: Thunderbird 2.0.0.9 (X11/20071115) MIME-Version: 1.0 To: Jeff Davis CC: linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] badness() dramatically overcounts memory References: <1202182480.24634.22.camel@dogma.ljc.laika.com> In-Reply-To: <1202182480.24634.22.camel@dogma.ljc.laika.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Jeff Davis wrote: > In oom_kill.c, one of the badness calculations is wildly inaccurate. If > memory is shared among child processes, that same memory will be counted > for each child, effectively multiplying the memory penalty by N, where N > is the number of children. > > This makes it almost certain that the parent will always be chosen as > the victim of the OOM killer (assuming any substantial amount memory > shared among the children), even if the parent and children are well > behaved and have a reasonable and unchanging VM size. > > Usually this does not actually alleviate the memory pressure because the > truly bad process is completely unrelated; and the OOM killer must later > kill the truly bad process. > > This trivial patch corrects the calculation so that it does not count a > child's shared memory against the parent. > Hi, Jeff, 1. grep on the kernel source tells me that shared_vm is incremented only in vm_stat_account(), which is a NO-OP if CONFIG_PROC_FS is not defined. 2. How have you tested these patches? One way to do it would be to use the memory controller and set a small limit on the control group. A memory intensive application will soon see an OOM. I do need to look at OOM kill sanity, my colleagues using the memory controller have reported wrong actions taken by the OOM killer, but I am yet to analyze them. The interesting thing is the use of total_vm and not the RSS which is used as the basis by the OOM killer. I need to read/understand the code a bit more. -- Warm Regards, Balbir Singh Linux Technology Center IBM, ISTL