Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756305Ab0DNQXL (ORCPT ); Wed, 14 Apr 2010 12:23:11 -0400 Received: from smtp-out.google.com ([74.125.121.35]:56031 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756275Ab0DNQXI convert rfc822-to-8bit (ORCPT ); Wed, 14 Apr 2010 12:23:08 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=mime-version:in-reply-to:references:from:date:message-id: subject:to:cc:content-type:content-transfer-encoding:x-system-of-record; b=HYjkuJxnJO8GmV3Hrdlmi8zT20Fbh9bWNU4F1NPu64qXWHmjypE9tUeai5U40miDJ CknoPHm2Iv1DRC+tdjeEQ== MIME-Version: 1.0 In-Reply-To: <20100414182904.2f72a63d.kamezawa.hiroyu@jp.fujitsu.com> References: <1268609202-15581-1-git-send-email-arighi@develer.com> <20100318085411.834e1e46.kamezawa.hiroyu@jp.fujitsu.com> <20100318041944.GA18054@balbir.in.ibm.com> <20100318133527.420b2f25.kamezawa.hiroyu@jp.fujitsu.com> <20100318162855.GG18054@balbir.in.ibm.com> <20100319102332.f1d81c8d.kamezawa.hiroyu@jp.fujitsu.com> <20100319024039.GH18054@balbir.in.ibm.com> <20100319120049.3dbf8440.kamezawa.hiroyu@jp.fujitsu.com> <20100414182904.2f72a63d.kamezawa.hiroyu@jp.fujitsu.com> From: Greg Thelen Date: Wed, 14 Apr 2010 09:22:41 -0700 Message-ID: Subject: Re: [PATCH -mmotm 1/5] memcg: disable irq at page cgroup lock To: KAMEZAWA Hiroyuki Cc: balbir@linux.vnet.ibm.com, Andrea Righi , Daisuke Nishimura , Vivek Goyal , Peter Zijlstra , Trond Myklebust , Suleiman Souhlal , "Kirill A. Shutemov" , Andrew Morton , containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4594 Lines: 112 On Wed, Apr 14, 2010 at 2:29 AM, KAMEZAWA Hiroyuki wrote: > On Tue, 13 Apr 2010 23:55:12 -0700 > Greg Thelen wrote: >> On Thu, Mar 18, 2010 at 8:00 PM, KAMEZAWA Hiroyuki wrote: >> > On Fri, 19 Mar 2010 08:10:39 +0530 >> > Balbir Singh wrote: >> >> * KAMEZAWA Hiroyuki [2010-03-19 10:23:32]: >> >> >> >> > On Thu, 18 Mar 2010 21:58:55 +0530 >> >> > Balbir Singh wrote: >> >> > >> >> > > * KAMEZAWA Hiroyuki [2010-03-18 13:35:27]: >> >> > >> >> > > > Then, no probelm. It's ok to add mem_cgroup_udpate_stat() indpendent from >> >> > > > mem_cgroup_update_file_mapped(). The look may be messy but it's not your >> >> > > > fault. But please write "why add new function" to patch description. >> >> > > > >> >> > > > I'm sorry for wasting your time. >> >> > > >> >> > > Do we need to go down this route? We could check the stat and do the >> >> > > correct thing. In case of FILE_MAPPED, always grab page_cgroup_lock >> >> > > and for others potentially look at trylock. It is OK for different >> >> > > stats to be protected via different locks. >> >> > > >> >> > >> >> > I _don't_ want to see a mixture of spinlock and trylock in a function. >> >> > >> >> >> >> A well documented well written function can help. The other thing is to >> >> of-course solve this correctly by introducing different locking around >> >> the statistics. Are you suggesting the later? >> >> >> > >> > No. As I wrote. >> > ? ? ? ?- don't modify codes around FILE_MAPPED in this series. >> > ? ? ? ?- add a new functions for new statistics >> > Then, >> > ? ? ? ?- think about clean up later, after we confirm all things work as expected. >> >> I have ported Andrea Righi's memcg dirty page accounting patches to latest >> mmtom-2010-04-05-16-09. ?In doing so I have to address this locking issue. ?Does >> the following look good? ?I will (of course) submit the entire patch for review, >> but I wanted make sure I was aiming in the right direction. >> >> void mem_cgroup_update_page_stat(struct page *page, >> ? ? ? ? ? ? ? ? ? ? ? enum mem_cgroup_write_page_stat_item idx, bool charge) >> { >> ? ? ? static int seq; >> ? ? ? struct page_cgroup *pc; >> >> ? ? ? if (mem_cgroup_disabled()) >> ? ? ? ? ? ? ? return; >> ? ? ? pc = lookup_page_cgroup(page); >> ? ? ? if (!pc || mem_cgroup_is_root(pc->mem_cgroup)) >> ? ? ? ? ? ? ? return; >> >> ? ? ? /* >> ? ? ? ?* This routine does not disable irq when updating stats. ?So it is >> ? ? ? ?* possible that a stat update from within interrupt routine, could >> ? ? ? ?* deadlock. ?Use trylock_page_cgroup() to avoid such deadlock. ?This >> ? ? ? ?* makes the memcg counters fuzzy. ?More complicated, or lower >> ? ? ? ?* performing locking solutions avoid this fuzziness, but are not >> ? ? ? ?* currently needed. >> ? ? ? ?*/ >> ? ? ? if (irqs_disabled()) { >> ? ? ? ? ? ? ? if (! trylock_page_cgroup(pc)) >> ? ? ? ? ? ? ? ? ? ? ? return; >> ? ? ? } else >> ? ? ? ? ? ? ? lock_page_cgroup(pc); >> > > I prefer trylock_page_cgroup() always. What is your reason for preferring trylock_page_cgroup()? I assume it's for code simplicity, but I wanted to check. I had though about using trylock_page_cgroup() always, but I think that would make file_mapped accounting even more fuzzy that it already it is. I was trying to retain the current accuracy of file_mapped and only make new counters, like writeback/dirty/etc (those obtained in interrupt), fuzzy. > I have another idea fixing this up _later_. (But I want to start from simple one.) > > My rough idea is following. ?Similar to your idea which you gave me before. Hi Kame-san, I like the general approach. The code I previously gave you appears to work and is faster than non-root memcgs using mmotm due to mostly being lockless. > == > DEFINE_PERCPU(account_move_ongoing); What's the reason for having a per-cpu account_move_ongoing flag? Would a single system-wide global be sufficient? I assume the majority of the time this value will not be changing because accounting moves are rare. Perhaps all of the per-cpu variables are packed within a per-cpu cacheline making accessing it more likely to be local, but I'm not sure if this is true. -- Greg -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/