From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751504Ab2GIFW7 (ORCPT ); Mon, 9 Jul 2012 01:22:59 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:37664 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750756Ab2GIFW5 (ORCPT ); Mon, 9 Jul 2012 01:22:57 -0400 Message-ID: <4FFA6AAE.8030700@gmail.com> Date: Mon, 09 Jul 2012 13:22:54 +0800 From: Sha Zhengju User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.23) Gecko/20110922 Thunderbird/3.1.15 MIME-Version: 1.0 To: Kamezawa Hiroyuki CC: Fengguang Wu , linux-mm@kvack.org, cgroups@vger.kernel.org, gthelen@google.com, yinghan@google.com, akpm@linux-foundation.org, mhocko@suse.cz, linux-kernel@vger.kernel.org, Sha Zhengju Subject: Re: [PATCH 6/7] memcg: add per cgroup writeback pages accounting References: <1340880885-5427-1-git-send-email-handai.szj@taobao.com> <1340881562-5900-1-git-send-email-handai.szj@taobao.com> <20120708145309.GC18272@localhost> <4FFA51AB.30203@gmail.com> <20120709041437.GA10180@localhost> <4FFA5B7F.8030403@jp.fujitsu.com> In-Reply-To: <4FFA5B7F.8030403@jp.fujitsu.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/09/2012 12:18 PM, Kamezawa Hiroyuki wrote: > (2012/07/09 13:14), Fengguang Wu wrote: >> On Mon, Jul 09, 2012 at 11:36:11AM +0800, Sha Zhengju wrote: >>> On 07/08/2012 10:53 PM, Fengguang Wu wrote: >>>>> @@ -2245,7 +2252,10 @@ int test_set_page_writeback(struct page *page) >>>>> { >>>>> struct address_space *mapping = page_mapping(page); >>>>> int ret; >>>>> + bool locked; >>>>> + unsigned long flags; >>>>> >>>>> + mem_cgroup_begin_update_page_stat(page,&locked,&flags); >>>>> if (mapping) { >>>>> struct backing_dev_info *bdi = mapping->backing_dev_info; >>>>> unsigned long flags; >>>>> @@ -2272,6 +2282,8 @@ int test_set_page_writeback(struct page *page) >>>>> } >>>>> if (!ret) >>>>> account_page_writeback(page); >>>>> + >>>>> + mem_cgroup_end_update_page_stat(page,&locked,&flags); >>>>> return ret; >>>>> >>>>> } >>>> Where is the MEM_CGROUP_STAT_FILE_WRITEBACK increased? >>>> >>> >>> It's in account_page_writeback(). >>> >>> void account_page_writeback(struct page *page) >>> { >>> + mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_FILE_WRITEBACK); >>> inc_zone_page_state(page, NR_WRITEBACK); >>> } >> >> I didn't find that chunk, perhaps it's lost due to rebase.. >> >>> There isn't a unified interface to dec/inc writeback accounting, so >>> I just follow that. >>> Maybe we can rework account_page_writeback() to also account >>> dec in? >> >> The current seperate inc/dec paths are fine. It sounds like >> over-engineering if going any further. >> >> I'm a bit worried about some 3rd party kernel module to call >> account_page_writeback() without >> mem_cgroup_begin/end_update_page_stat(). >> Will that lead to serious locking issues, or merely inaccurate >> accounting? >> > > Ah, Hm. Maybe it's better to add some debug check in > mem_cgroup_update_page_stat(). rcu_read_lock_held() or some. > This also apply to account_page_dirtied()... But as an "range" lock, I think it's common in current kernel: just as set_page_dirty(), the caller should call it under the page lock (in most cases) and it's his responsibility to guarantee correctness. I can add some comments or debug check as reminding but I think i can only do so... Thanks, Sha