Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757781Ab2JSRNw (ORCPT ); Fri, 19 Oct 2012 13:13:52 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51273 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751359Ab2JSRNv (ORCPT ); Fri, 19 Oct 2012 13:13:51 -0400 Message-ID: <50818A41.7030909@redhat.com> Date: Fri, 19 Oct 2012 13:13:37 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120827 Thunderbird/15.0 MIME-Version: 1.0 To: Peter Zijlstra CC: Andrea Arcangeli , Ingo Molnar , Linux Memory Management List , Mel Gorman , Linux kernel Mailing List Subject: Re: question on NUMA page migration References: <5081777A.8050104@redhat.com> <1350664742.2768.40.camel@twins> In-Reply-To: <1350664742.2768.40.camel@twins> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1250 Lines: 40 On 10/19/2012 12:39 PM, Peter Zijlstra wrote: > On Fri, 2012-10-19 at 11:53 -0400, Rik van Riel wrote: >> >> If we do need the extra refcount, why is normal >> page migration safe? :) > > Its mostly a matter of how convoluted you make the code, regular page > migration is about as bad as you can get > > Normal does: > > follow_page(FOLL_GET) +1 > > isolate_lru_page() +1 > > put_page() -1 > > ending up with a page with a single reference (for anon, or one extra > each for the mapping and buffer). Would it make sense to have the normal page migration code always work with the extra refcount, so we do not have to introduce a new MIGRATE_FAULT migration mode? On the other hand, compaction does not take the extra reference... Another alternative might be to do the put_page inside do_prot_none_numa(). That would be analogous to do_wp_page disposing of the old page for the caller. I am not real happy about NUMA migration introducing its own migration mode... -- All rights reversed -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/