From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx165.postini.com [74.125.245.165]) by kanga.kvack.org (Postfix) with SMTP id 318A66B002C for ; Thu, 8 Mar 2012 21:33:51 -0500 (EST) Received: by iajr24 with SMTP id r24so2116112iaj.14 for ; Thu, 08 Mar 2012 18:33:50 -0800 (PST) Date: Thu, 8 Mar 2012 18:33:14 -0800 (PST) From: Hugh Dickins Subject: Re: [PATCH v3 2/2] memcg: avoid THP split in task migration In-Reply-To: <20120309101658.8b36ce4f.kamezawa.hiroyu@jp.fujitsu.com> Message-ID: 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 Sender: owner-linux-mm@kvack.org List-ID: To: KAMEZAWA Hiroyuki Cc: Naoya Horiguchi , linux-mm@kvack.org, Andrew Morton , Andrea Arcangeli , Daisuke Nishimura , Hillf Danton , linux-kernel@vger.kernel.org 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. And it's not how it has been and continues to behave with file pages. Isn't getting that behaviour in fork-move-exec just a good reason not to set move_charge_at_immigrate? 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(). I'd rather delete than add code here! Hugh -- 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