From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757585AbXIRTaa (ORCPT ); Tue, 18 Sep 2007 15:30:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754526AbXIRTaX (ORCPT ); Tue, 18 Sep 2007 15:30:23 -0400 Received: from netops-testserver-4-out.sgi.com ([192.48.171.29]:58942 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753012AbXIRTaX (ORCPT ); Tue, 18 Sep 2007 15:30:23 -0400 Date: Tue, 18 Sep 2007 12:30:20 -0700 (PDT) From: Christoph Lameter X-X-Sender: clameter@schroedinger.engr.sgi.com To: Andi Kleen cc: Lee Schermerhorn , linux-kernel , akpm@linux-foundation.org, eric.whitney@hp.com, Mel Gorman Subject: Re: [PATCH] 2.6.23-rc6: Fix NUMA Memory Policy Reference Counting In-Reply-To: <200709180025.40837.ak@suse.de> Message-ID: References: <20070830185053.22619.96398.sendpatchset@localhost> <1190057534.5460.131.camel@localhost> <200709180025.40837.ak@suse.de> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 18 Sep 2007, Andi Kleen wrote: > > The patch does require concurrent increments and decrements in the main > > fault patch. The potential is to create another bouncing cacheline for > > concurrent faults. This looks like it would cause a performance issue. > > While may be true correctness is always more important than performance. > So I think this is the right thing for .23. Any performance improvements > if needed can come later. Is there any real issue as a result of the refcounting issues? It seems that performance improvements are not possible unless one would modify how memory policies work using RCU or so. Ok the effect is limited. get_vma_policy() only increments refcounts for foreign or shared policies. So it seems that it is fine if one stays away from shmem.