From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750729AbWAPMbs (ORCPT ); Mon, 16 Jan 2006 07:31:48 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750730AbWAPMbs (ORCPT ); Mon, 16 Jan 2006 07:31:48 -0500 Received: from gold.veritas.com ([143.127.12.110]:54083 "EHLO gold.veritas.com") by vger.kernel.org with ESMTP id S1750729AbWAPMbs (ORCPT ); Mon, 16 Jan 2006 07:31:48 -0500 Date: Mon, 16 Jan 2006 12:32:14 +0000 (GMT) From: Hugh Dickins X-X-Sender: hugh@goblin.wat.veritas.com To: Christoph Lameter cc: Nick Piggin , Andrew Morton , Linux Kernel Mailing List , Linux Memory Management List Subject: Re: Race in new page migration code? In-Reply-To: Message-ID: References: <20060114155517.GA30543@wotan.suse.de> <20060114181949.GA27382@wotan.suse.de> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-OriginalArrivalTime: 16 Jan 2006 12:31:43.0496 (UTC) FILETIME=[CEE2D080:01C61A98] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 15 Jan 2006, Christoph Lameter wrote: > On Sun, 15 Jan 2006, Hugh Dickins wrote: > > > > Good. And whether it's your or Nick's patch that goes in, please also > > remove that PageReserved test which you recently put in check_pte_range. > > Zero pages are still marked reserved AFAIK. Why not check for it? Indeed they are, at present and quite likely into posterity. But they're not a common case here, and migrate_page_add now handles them silently, so why bother to complicate it with an unnecessary check? You added the test because the WARN_ON fired, you're now doing the right thing and removing the WARN_ON because it was inevitably racy, so it would make sense to remove the PageReserved test too. If you look through the rest of mm/, you'll find 2.6.15 removed all the PageReserved tests, except at the low level in page_alloc.c: so it's retrograde for you to be adding one back here. Testing PageLRU would be more relevant, if you insist on such a test. Or have you found the zero page mapcount distorting get_stats stats? If that's an issue, then better add a commented test for it there. Hmm, that battery of unusual tests at the start of migrate_page_add is odd: the tests don't quite match the comment, and it isn't clear what reasoning lies behind the comment anyway. Hugh