Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755844Ab0DNOod (ORCPT ); Wed, 14 Apr 2010 10:44:33 -0400 Received: from e23smtp08.au.ibm.com ([202.81.31.141]:46773 "EHLO e23smtp08.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755814Ab0DNOoc (ORCPT ); Wed, 14 Apr 2010 10:44:32 -0400 Date: Wed, 14 Apr 2010 20:14:24 +0530 From: Balbir Singh To: Greg Thelen Cc: KAMEZAWA Hiroyuki , 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 Subject: Re: [PATCH -mmotm 1/5] memcg: disable irq at page cgroup lock Message-ID: <20100414144424.GN3994@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com 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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.20 (2009-08-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4316 Lines: 127 * Greg Thelen [2010-04-13 23:55:12]: > 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; Since this is just stats can we used deferred updates? else update a deferred structure > } else > lock_page_cgroup(pc); > > __mem_cgroup_update_page_stat(pc, idx, charge); Do charging + any deferred charges pending in __mem_cgroup_update_page_stat(). > 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 = 0; > } else { > if (PageCgroupFileMapped(pc)) > ClearPageCgroupFileMapped(pc); > else > val = 0; > } > idx = 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. > -- Three Cheers, Balbir -- 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/