From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx199.postini.com [74.125.245.199]) by kanga.kvack.org (Postfix) with SMTP id 03F096B007E for ; Thu, 8 Mar 2012 22:26:28 -0500 (EST) Received: from m2.gw.fujitsu.co.jp (unknown [10.0.50.72]) by fgwmail5.fujitsu.co.jp (Postfix) with ESMTP id 42E743EE0AE for ; Fri, 9 Mar 2012 12:26:27 +0900 (JST) Received: from smail (m2 [127.0.0.1]) by outgoing.m2.gw.fujitsu.co.jp (Postfix) with ESMTP id 2C9E845DD78 for ; Fri, 9 Mar 2012 12:26:27 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (s2.gw.fujitsu.co.jp [10.0.50.92]) by m2.gw.fujitsu.co.jp (Postfix) with ESMTP id 0D50545DD74 for ; Fri, 9 Mar 2012 12:26:27 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id 001131DB8038 for ; Fri, 9 Mar 2012 12:26:26 +0900 (JST) Received: from m105.s.css.fujitsu.com (m105.s.css.fujitsu.com [10.240.81.145]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id A00A01DB803A for ; Fri, 9 Mar 2012 12:26:26 +0900 (JST) Date: Fri, 9 Mar 2012 12:24:48 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH v3 2/2] memcg: avoid THP split in task migration Message-Id: <20120309122448.92931dc6.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: References: <1330719189-20047-1-git-send-email-n-horiguchi@ah.jp.nec.com> <1330719189-20047-2-git-send-email-n-horiguchi@ah.jp.nec.com> <20120309101658.8b36ce4f.kamezawa.hiroyu@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: Naoya Horiguchi , linux-mm@kvack.org, Andrew Morton , Andrea Arcangeli , Daisuke Nishimura , Hillf Danton , linux-kernel@vger.kernel.org"nishimura@mxp.nes.nec.co.jp" On Thu, 8 Mar 2012 18:33:14 -0800 (PST) Hugh Dickins wrote: > On Fri, 9 Mar 2012, KAMEZAWA Hiroyuki wrote: > > > + > > > + page = pmd_page(pmd); > > > + VM_BUG_ON(!page || !PageHead(page)); > > > + if (!move_anon() || page_mapcount(page) != 1) > > > + return 0; > > > > Could you add this ? > > == > > static bool move_check_shared_map(struct page *page) > > { > > /* > > * Handling of shared pages between processes is a big trouble in memcg. > > * Now, we never move shared-mapped pages between memcg at 'task' moving because > > * we have no hint which task the page is really belongs to. For example, > > * When a task does "fork()-> move to the child other group -> exec()", the charges > > * should be stay in the original cgroup. > > * So, check mapcount to determine we can move or not. > > */ > > return page_mapcount(page) != 1; > > } > > That's a helpful elucidation, thank you. However... > > That is not how it has actually been behaving for the last 18 months > (because of the "> 2" bug), so in practice you are asking for a change > in behaviour there. > Yes. > And it's not how it has been and continues to behave with file pages. > It's ok to add somethink like.. if (PageAnon(page) && !move_anon()) return false; ... > Isn't getting that behaviour in fork-move-exec just a good reason not > to set move_charge_at_immigrate? > Hmm. Maybe. > I think there are other scenarios where you do want all the pages to > move if move_charge_at_immigrate: and that's certainly easier to > describe and to understand and to code. > > But if you do insist on not moving the shared, then it needs to involve > something like mem_cgroup_count_swap_user() on PageSwapCache pages, > rather than just the bare page_mapcount(). > This 'moving swap account' was a requirement from a user (NEC?). But no user doesn't say 'I want to move shared pages between cgroups at task move !' and I don't like to move shared objects. > I'd rather delete than add code here! > As a user, for Fujitsu, I believe it's insane to move task between cgroups. So, I have no benefit from this code, at all. Ok, maybe I'm not a stakeholder,here. If users say all shared pages should be moved, ok, let's move. But change of behavior should be documented and implemented in an independet patch. CC'ed Nishimura-san, he implemetned this, a real user. 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org