From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id B9015600374 for ; Wed, 14 Apr 2010 02:55:53 -0400 (EDT) Subject: Re: [PATCH -mmotm 1/5] memcg: disable irq at page cgroup lock References: <1268609202-15581-1-git-send-email-arighi@develer.com> <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> From: Greg Thelen Date: Tue, 13 Apr 2010 23:55:12 -0700 In-Reply-To: (Greg Thelen's message of "Tue\, 13 Apr 2010 23\:37\:33 -0700") 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: 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 List-ID: 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 10:23:3= 2]: >> >> > 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() indpende= nt from >> > > > mem_cgroup_update_file_mapped(). The look may be messy but it's no= t your >> > > > fault. But please write "why add new function" to patch descriptio= n. >> > > > >> > > > 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. > =C2=A0 =C2=A0 =C2=A0 =C2=A0- don't modify codes around FILE_MAPPED in thi= s 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 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 re= view, 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 =3D 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); __mem_cgroup_update_page_stat(pc, idx, charge); unlock_page_cgroup(pc); } __mem_cgroup_update_page_stat() has a switch statement that updates all of = the MEMCG_NR_FILE_{MAPPED,DIRTY,WRITEBACK,WRITEBACK_TEMP,UNSTABLE_NFS} counters using the following form: switch (idx) { case MEMCG_NR_FILE_MAPPED: if (charge) { if (!PageCgroupFileMapped(pc)) SetPageCgroupFileMapped(pc); else val =3D 0; } else { if (PageCgroupFileMapped(pc)) ClearPageCgroupFileMapped(pc); else val =3D 0; } idx =3D MEM_CGROUP_STAT_FILE_MAPPED; break; ... } /* * Preemption is already disabled. We can use __this_cpu_xxx */ if (val > 0) { __this_cpu_inc(mem->stat->count[idx]); } else if (val < 0) { __this_cpu_dec(mem->stat->count[idx]); } In my current tree, irq is never saved/restored by cgroup locking code. To protect against interrupt reentrancy, trylock_page_cgroup() is used. As the comment indicates, this makes the new counters fuzzy. -- 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