From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965135AbbEMNIG (ORCPT ); Wed, 13 May 2015 09:08:06 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38069 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933388AbbEMNIC (ORCPT ); Wed, 13 May 2015 09:08:02 -0400 Message-ID: <55534CA2.7030105@redhat.com> Date: Wed, 13 May 2015 09:07:46 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Mel Gorman , Andrew Morton CC: linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm, numa: Really disable NUMA balancing by default on single node machines References: <20150513081053.GQ2462@suse.de> In-Reply-To: <20150513081053.GQ2462@suse.de> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/13/2015 04:10 AM, Mel Gorman wrote: > NUMA balancing is meant to be disabled by default on UMA machines but > the check is using nr_node_ids (highest node) instead of num_online_nodes > (online nodes). The consequences are that a UMA machine with a node ID of 1 > or higher will enable NUMA balancing. This will incur useless overhead due > to minor faults with the impact depending on the workload. These are the > impact on the stats when running a kernel build on a single node machine > whose node ID happened to be 1; > > vanilla patched > NUMA base PTE updates 5113158 0 > NUMA huge PMD updates 643 0 > NUMA page range updates 5442374 0 > NUMA hint faults 2109622 0 > NUMA hint local faults 2109622 0 > NUMA hint local percent 100 100 > NUMA pages migrated 0 0 > > Signed-off-by: Mel Gorman > Cc: #v3.8+ Reviewed-by: Rik van Riel -- All rights reversed