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 ESMTP id 7EFE36B0093 for ; Tue, 21 Apr 2009 23:20:18 -0400 (EDT) Received: from d23relay01.au.ibm.com (d23relay01.au.ibm.com [202.81.31.243]) by e23smtp09.au.ibm.com (8.13.1/8.13.1) with ESMTP id n3M2wGLN012441 for ; Tue, 21 Apr 2009 22:58:16 -0400 Received: from d23av04.au.ibm.com (d23av04.au.ibm.com [9.190.235.139]) by d23relay01.au.ibm.com (8.13.8/8.13.8/NCO v9.2) with ESMTP id n3M3KSmT405790 for ; Wed, 22 Apr 2009 13:20:31 +1000 Received: from d23av04.au.ibm.com (loopback [127.0.0.1]) by d23av04.au.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id n3M3KS12029191 for ; Wed, 22 Apr 2009 13:20:28 +1000 Date: Wed, 22 Apr 2009 08:49:39 +0530 From: Balbir Singh Subject: Re: [PATCH] Add file based RSS accounting for memory resource controller (v3) Message-ID: <20090422031939.GQ19637@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com References: <20090417110350.3144183d.kamezawa.hiroyu@jp.fujitsu.com> <20090417034539.GD18558@balbir.in.ibm.com> <20090417124951.a8472c86.kamezawa.hiroyu@jp.fujitsu.com> <20090417045623.GA3896@balbir.in.ibm.com> <20090417141726.a69ebdcc.kamezawa.hiroyu@jp.fujitsu.com> <20090417064726.GB3896@balbir.in.ibm.com> <20090417155608.eeed1f02.kamezawa.hiroyu@jp.fujitsu.com> <20090417141837.GD3896@balbir.in.ibm.com> <20090421132551.38e9960a.akpm@linux-foundation.org> <20090422090218.6d451a08.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20090422090218.6d451a08.kamezawa.hiroyu@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: * KAMEZAWA Hiroyuki [2009-04-22 09:02:18]: > On Tue, 21 Apr 2009 13:25:51 -0700 > Andrew Morton wrote: > > > On Fri, 17 Apr 2009 19:48:38 +0530 > > Balbir Singh wrote: > > > > > > > > ... > > > > > > We currently don't track file RSS, the RSS we report is actually anon RSS. > > > All the file mapped pages, come in through the page cache and get accounted > > > there. This patch adds support for accounting file RSS pages. It should > > > > > > 1. Help improve the metrics reported by the memory resource controller > > > 2. Will form the basis for a future shared memory accounting heuristic > > > that has been proposed by Kamezawa. > > > > > > Unfortunately, we cannot rename the existing "rss" keyword used in memory.stat > > > to "anon_rss". We however, add "mapped_file" data and hope to educate the end > > > user through documentation. > > > > > > Signed-off-by: Balbir Singh > > > > > > ... > > > > > > @@ -1096,6 +1135,10 @@ static int mem_cgroup_move_account(struct page_cgroup *pc, > > > struct mem_cgroup_per_zone *from_mz, *to_mz; > > > int nid, zid; > > > int ret = -EBUSY; > > > + struct page *page; > > > + int cpu; > > > + struct mem_cgroup_stat *stat; > > > + struct mem_cgroup_stat_cpu *cpustat; > > > > > > VM_BUG_ON(from == to); > > > VM_BUG_ON(PageLRU(pc->page)); > > > @@ -1116,6 +1159,23 @@ static int mem_cgroup_move_account(struct page_cgroup *pc, > > > > > > res_counter_uncharge(&from->res, PAGE_SIZE); > > > mem_cgroup_charge_statistics(from, pc, false); > > > + > > > + page = pc->page; > > > + if (page_is_file_cache(page) && page_mapped(page)) { > > > + cpu = smp_processor_id(); > > > + /* Update mapped_file data for mem_cgroup "from" */ > > > + stat = &from->stat; > > > + cpustat = &stat->cpustat[cpu]; > > > + __mem_cgroup_stat_add_safe(cpustat, MEM_CGROUP_STAT_MAPPED_FILE, > > > + -1); > > > + > > > + /* Update mapped_file data for mem_cgroup "to" */ > > > + stat = &to->stat; > > > + cpustat = &stat->cpustat[cpu]; > > > + __mem_cgroup_stat_add_safe(cpustat, MEM_CGROUP_STAT_MAPPED_FILE, > > > + 1); > > > + } > > > > This function (mem_cgroup_move_account()) does a trylock_page_cgroup() > > and if that fails it will bale out, and the newly-added code will not > > be executed. > yes. and returns -EBUSY. > > > > > What are the implications of this? Does the missed accounting later get > > performed somewhere, or does the error remain in place? > > > no error just -BUSY. the caller (now, only force_empty is the caller) will do retry. > > > That trylock_page_cgroup() really sucks - trylocks usually do. Could > > someone please raise a patch which completely documents the reasons for > > its presence, and for any other uncommented/unobvious trylocks? > > > > Where appropriate, the comment should explain why the trylock isn't > > simply a bug - why it is safe and correct to omit the operations which > > we wished to perform. > > > > Thanks. > > > Hmm...maybe we can replace trylock with lock, here. > > IIRC, this has been trylock because the old routine uses other locks > (mem_cgroup' zone mz->lru_lock) before calling this. > mz->lru_lock > lock_page_cgroup() > And there was other routine which calls lock_page_cgroup()->mz->lru_lock. > lock_page_cgroup() > -> mz->lru_lock. > > So, I used trylock here. But now, the lock(mz->lru_lock) is removed. > I should check this. > > Thank you for pointing out. > This is definitely worth looking into. Since we run force_empty() in a while loop with some margin, we've probably avoided the problem. I think this code needs a second look and refactoring. -- Balbir -- 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