From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx142.postini.com [74.125.245.142]) by kanga.kvack.org (Postfix) with SMTP id 014946B0072 for ; Mon, 9 Jul 2012 01:28:23 -0400 (EDT) Date: Mon, 9 Jul 2012 13:28:13 +0800 From: Fengguang Wu Subject: Re: [PATCH 6/7] memcg: add per cgroup writeback pages accounting Message-ID: <20120709052813.GB11126@localhost> 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> <4FFA6AAE.8030700@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4FFA6AAE.8030700@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Sha Zhengju Cc: Kamezawa Hiroyuki , 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 On Mon, Jul 09, 2012 at 01:22:54PM +0800, Sha Zhengju wrote: > 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... Yeah, it helps to add some brief comment on the locking rule in account_page_*(). Thanks, Fengguang -- 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