From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with ESMTP id B83126B01E3 for ; Wed, 14 Apr 2010 16:14:38 -0400 (EDT) From: Greg Thelen Subject: Re: [PATCH -mmotm 1/5] memcg: disable irq at page cgroup lock References: <1268609202-15581-2-git-send-email-arighi@develer.com> <20100317115855.GS18054@balbir.in.ibm.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> <20100414140523.GC13535@redhat.com> Date: Wed, 14 Apr 2010 13:14:07 -0700 In-Reply-To: <20100414140523.GC13535@redhat.com> (Vivek Goyal's message of "Wed, 14 Apr 2010 10:05:23 -0400") Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org To: Vivek Goyal Cc: KAMEZAWA Hiroyuki , balbir@linux.vnet.ibm.com, Andrea Righi , Daisuke Nishimura , 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 List-ID: Vivek Goyal writes: > On Tue, Apr 13, 2010 at 11:55:12PM -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 10:2= 3:32]: >> >> >> >> > 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() indpe= ndent 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 descrip= tion. >> >> > > > >> >> > > > 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_lo= ck >> >> > > 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 functi= on. >> >> > >> >> >> >> 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. >> > =C2=A0 =C2=A0 =C2=A0 =C2=A0- don't modify codes around FILE_MAPPED in = this series. >> > =C2=A0 =C2=A0 =C2=A0 =C2=A0- add a new functions for new statistics >> > Then, >> > =C2=A0 =C2=A0 =C2=A0 =C2=A0- think about clean up later, after we conf= irm all things work as expected. >>=20 >> I have ported Andrea Righi's memcg dirty page accounting patches to late= st >> mmtom-2010-04-05-16-09. In doing so I have to address this locking issu= e. 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. >>=20 >> 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; >>=20 >> if (mem_cgroup_disabled()) >> return; >> pc =3D lookup_page_cgroup(page); >> if (!pc || mem_cgroup_is_root(pc->mem_cgroup)) >> return; >>=20 >> /* >> * 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()) { > ^^^^^^^^^ > Or may be in_interrupt()? Good catch. I will replace irqs_disabled() with in_interrupt(). Thank you. -- Greg -- 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