From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id 9A9116B01F5 for ; Tue, 27 Apr 2010 20:32:07 -0400 (EDT) Received: from m6.gw.fujitsu.co.jp ([10.0.50.76]) by fgwmail7.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id o3S0W4M0025843 for (envelope-from kamezawa.hiroyu@jp.fujitsu.com); Wed, 28 Apr 2010 09:32:04 +0900 Received: from smail (m6 [127.0.0.1]) by outgoing.m6.gw.fujitsu.co.jp (Postfix) with ESMTP id EA70045DE4E for ; Wed, 28 Apr 2010 09:32:03 +0900 (JST) Received: from s6.gw.fujitsu.co.jp (s6.gw.fujitsu.co.jp [10.0.50.96]) by m6.gw.fujitsu.co.jp (Postfix) with ESMTP id 6001545DE4C for ; Wed, 28 Apr 2010 09:32:03 +0900 (JST) Received: from s6.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s6.gw.fujitsu.co.jp (Postfix) with ESMTP id C10971DB8023 for ; Wed, 28 Apr 2010 09:32:02 +0900 (JST) Received: from m107.s.css.fujitsu.com (m107.s.css.fujitsu.com [10.249.87.107]) by s6.gw.fujitsu.co.jp (Postfix) with ESMTP id D161B1DB801A for ; Wed, 28 Apr 2010 09:32:01 +0900 (JST) Date: Wed, 28 Apr 2010 09:28:02 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH 1/3] mm,migration: During fork(), wait for migration to end if migration PTE is encountered Message-Id: <20100428092802.816e2716.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <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> <20100428001911.GG510@random.random> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Andrea Arcangeli Cc: Mel Gorman , Linux-MM , LKML , Minchan Kim , Christoph Lameter , Rik van Riel , Andrew Morton List-ID: On Wed, 28 Apr 2010 02:19:11 +0200 Andrea Arcangeli wrote: > 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 why we have to remove migration_pte by rmap_walk() which doesnt' exist ? Anyway, I agree there are no oops. But there are risks because migration is a feature which people don't tend to take care of (as memcg ;) I like conservative approach for this kind of features. Thanks, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org