From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755923Ab0D1AVJ (ORCPT ); Tue, 27 Apr 2010 20:21:09 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45312 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755668Ab0D1AVF (ORCPT ); Tue, 27 Apr 2010 20:21:05 -0400 Date: Wed, 28 Apr 2010 02:19:11 +0200 From: Andrea Arcangeli To: KAMEZAWA Hiroyuki Cc: Mel Gorman , Linux-MM , LKML , Minchan Kim , Christoph Lameter , Rik van Riel , Andrew Morton Subject: Re: [PATCH 1/3] mm,migration: During fork(), wait for migration to end if migration PTE is encountered Message-ID: <20100428001911.GG510@random.random> References: <1272403852-10479-1-git-send-email-mel@csn.ul.ie> <1272403852-10479-2-git-send-email-mel@csn.ul.ie> <20100427222245.GE8860@random.random> <20100428085203.4336b761.kamezawa.hiroyu@jp.fujitsu.com> <20100428001821.GF510@random.random> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100428001821.GF510@random.random> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 28, 2010 at 02:18:21AM +0200, Andrea Arcangeli wrote: > On Wed, Apr 28, 2010 at 08:52:03AM +0900, KAMEZAWA Hiroyuki wrote: > > I already explained this doesn't happend and said "I'm sorry". > > Oops I must have overlooked it sorry! I just seen the trace quoted in > the comment of the patch and that at least would need correction > before it can be pushed in mainline, or it creates huge confusion to > see a reverse trace for CPU A for an already tricky piece of code. > > > But considering maintainance, it's not necessary to copy migration ptes > > and we don't have to keep a fundamental risks of migration circus. > > > > So, I don't say "we don't need this patch." > > split_huge_page also has the same requirement and there is no bug to > fix, so I don't see why to make special changes for just migrate.c > when we still have to list_add_tail for split_huge_page. > > Furthermore this patch isn't fixing anything in any case and it looks > a noop to me. If the order ever gets inverted, and process2 ptes are > scanned before process1 ptes in the rmap_walk, sure the > copy-page-tables will break and stop until the process1 rmap_walk will > complete, but that is not enough! You have to repeat the rmap_walk of > process1 if the order ever gets inverted and this isn't happening in ^^^^^^^2 > the patch so I don't see how it could make any difference even just > for migrate.c (obviously not for split_huge_page).