From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753427Ab2IOK4p (ORCPT ); Sat, 15 Sep 2012 06:56:45 -0400 Received: from mail-lb0-f174.google.com ([209.85.217.174]:62242 "EHLO mail-lb0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751976Ab2IOK4m (ORCPT ); Sat, 15 Sep 2012 06:56:42 -0400 Message-ID: <50545EE4.5050004@openvz.org> Date: Sat, 15 Sep 2012 14:56:36 +0400 From: Konstantin Khlebnikov User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.7) Gecko/20120831 Firefox/10.0.7 Iceape/2.7.7 MIME-Version: 1.0 To: Hugh Dickins CC: Johannes Weiner , Wen Congyang , "linux-kernel@vger.kernel.org" , "cgroups@vger.kernel.org" , "linux-mm@kvack.org" , Jiang Liu , "mhocko@suse.cz" , "bsingharora@gmail.com" , KAMEZAWA Hiroyuki , Andrew Morton , "paul.gortmaker@windriver.com" Subject: Re: [PATCH] memory cgroup: update root memory cgroup when node is onlined References: <505187D4.7070404@cn.fujitsu.com> <20120913205935.GK1560@cmpxchg.org> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hugh Dickins wrote: > On Thu, 13 Sep 2012, Johannes Weiner wrote: >> On Thu, Sep 13, 2012 at 03:14:28PM +0800, Wen Congyang wrote: >>> root_mem_cgroup->info.nodeinfo is initialized when the system boots. >>> But NODE_DATA(nid) is null if the node is not onlined, so >>> root_mem_cgroup->info.nodeinfo[nid]->zoneinfo[zone].lruvec.zone contains >>> an invalid pointer. If we use numactl to bind a program to the node >>> after onlining the node and its memory, it will cause the kernel >>> panicked: >> >> Is there any chance we could get rid of the zone backpointer in lruvec >> again instead? > > It could be done, but it would make me sad :( Me too > >> Adding new nodes is a rare event and so updating every >> single memcg in the system might be just borderline crazy. > > Not horribly crazy, but rather ugly, yes. > >> But can't >> we just go back to passing the zone along with the lruvec down >> vmscan.c paths? I agree it's ugly to pass both, given their >> relationship. But I don't think the backpointer is any cleaner but in >> addition less robust. > > It's like how we use vma->mm: we could change everywhere to pass mm with > vma, but it looks cleaner and cuts down on long arglists to have mm in vma. > From past experience, one of the things I worried about was adding extra > args to the reclaim stack. > >> >> That being said, the crashing code in particular makes me wonder: >> >> static __always_inline void add_page_to_lru_list(struct page *page, >> struct lruvec *lruvec, enum lru_list lru) >> { >> int nr_pages = hpage_nr_pages(page); >> mem_cgroup_update_lru_size(lruvec, lru, nr_pages); >> list_add(&page->lru,&lruvec->lists[lru]); >> __mod_zone_page_state(lruvec_zone(lruvec), NR_LRU_BASE + lru, nr_pages); >> } >> >> Why did we ever pass zone in here and then felt the need to replace it >> with lruvec->zone in fa9add6 "mm/memcg: apply add/del_page to lruvec"? >> A page does not roam between zones, its zone is a static property that >> can be retrieved with page_zone(). > > Just as in vmscan.c, we have the lruvec to hand, and that's what we > mainly want to operate upon, but there is also some need for zone. > > (Both Konstantin and I were looking towards the day when we move the > lru_lock into the lruvec, removing more dependence on "zone". Pretty > much the only reason that hasn't happened yet, is that we have not found > time to make a performance case convincingly - but that's another topic.) > > Yes, page_zone(page) is a static property of the page, but it's not > necessarily cheap to evaluate: depends on how complex the memory model > and the spare page flags space, doesn't it? We both preferred to > derive zone from lruvec where convenient. > > How do you feel about this patch, and does it work for you guys? > > You'd be right if you guessed that I started out without the > mem_cgroup_zone_lruvec part of it, but oops in get_scan_count > told me that's needed too. > > Description to be filled in later: would it be needed for -stable, > or is onlining already broken in other ways that you're now fixing up? > > Reported-by: Tang Chen > Signed-off-by: Hugh Dickins > --- > > include/linux/mmzone.h | 2 - > mm/memcontrol.c | 40 ++++++++++++++++++++++++++++++++------- > mm/mmzone.c | 6 ----- > mm/page_alloc.c | 2 - > 4 files changed, 36 insertions(+), 14 deletions(-) > > --- 3.6-rc5/include/linux/mmzone.h 2012-08-03 08:31:26.892842267 -0700 > +++ linux/include/linux/mmzone.h 2012-09-13 17:07:51.893772372 -0700 > @@ -744,7 +744,7 @@ extern int init_currently_empty_zone(str > unsigned long size, > enum memmap_context context); > > -extern void lruvec_init(struct lruvec *lruvec, struct zone *zone); > +extern void lruvec_init(struct lruvec *lruvec); > > static inline struct zone *lruvec_zone(struct lruvec *lruvec) > { > --- 3.6-rc5/mm/memcontrol.c 2012-08-03 08:31:27.060842270 -0700 > +++ linux/mm/memcontrol.c 2012-09-13 17:46:36.870804625 -0700 > @@ -1061,12 +1061,25 @@ struct lruvec *mem_cgroup_zone_lruvec(st > struct mem_cgroup *memcg) > { > struct mem_cgroup_per_zone *mz; > + struct lruvec *lruvec; > > - if (mem_cgroup_disabled()) > - return&zone->lruvec; > + if (mem_cgroup_disabled()) { > + lruvec =&zone->lruvec; > + goto out; > + } > > mz = mem_cgroup_zoneinfo(memcg, zone_to_nid(zone), zone_idx(zone)); > - return&mz->lruvec; > + lruvec =&mz->lruvec; > +out: > + /* > + * Since a node can be onlined after the mem_cgroup was created, > + * we have to be prepared to initialize lruvec->zone here. > + */ > + if (unlikely(lruvec->zone != zone)) { > + VM_BUG_ON(lruvec->zone); > + lruvec->zone = zone; > + } > + return lruvec; > } Whoaaa, this makes me dizzy. I prefer hook in register_one_node(). BTW It would be nice to add notifier-chains into memory-hotplug. > > /* > @@ -1093,9 +1106,12 @@ struct lruvec *mem_cgroup_page_lruvec(st > struct mem_cgroup_per_zone *mz; > struct mem_cgroup *memcg; > struct page_cgroup *pc; > + struct lruvec *lruvec; > > - if (mem_cgroup_disabled()) > - return&zone->lruvec; > + if (mem_cgroup_disabled()) { > + lruvec =&zone->lruvec; > + goto out; > + } > > pc = lookup_page_cgroup(page); > memcg = pc->mem_cgroup; > @@ -1113,7 +1129,17 @@ struct lruvec *mem_cgroup_page_lruvec(st > pc->mem_cgroup = memcg = root_mem_cgroup; > > mz = page_cgroup_zoneinfo(memcg, page); > - return&mz->lruvec; > + lruvec =&mz->lruvec; > +out: > + /* > + * Since a node can be onlined after the mem_cgroup was created, > + * we have to be prepared to initialize lruvec->zone here. > + */ > + if (unlikely(lruvec->zone != zone)) { > + VM_BUG_ON(lruvec->zone); > + lruvec->zone = zone; > + } > + return lruvec; > } > > /** > @@ -4742,7 +4768,7 @@ static int alloc_mem_cgroup_per_zone_inf > > for (zone = 0; zone< MAX_NR_ZONES; zone++) { > mz =&pn->zoneinfo[zone]; > - lruvec_init(&mz->lruvec,&NODE_DATA(node)->node_zones[zone]); > + lruvec_init(&mz->lruvec); > mz->usage_in_excess = 0; > mz->on_tree = false; > mz->memcg = memcg; > --- 3.6-rc5/mm/mmzone.c 2012-08-03 08:31:27.064842271 -0700 > +++ linux/mm/mmzone.c 2012-09-13 17:06:28.921766001 -0700 > @@ -87,7 +87,7 @@ int memmap_valid_within(unsigned long pf > } > #endif /* CONFIG_ARCH_HAS_HOLES_MEMORYMODEL */ > > -void lruvec_init(struct lruvec *lruvec, struct zone *zone) > +void lruvec_init(struct lruvec *lruvec) > { > enum lru_list lru; > > @@ -95,8 +95,4 @@ void lruvec_init(struct lruvec *lruvec, > > for_each_lru(lru) > INIT_LIST_HEAD(&lruvec->lists[lru]); > - > -#ifdef CONFIG_MEMCG > - lruvec->zone = zone; > -#endif > } > --- 3.6-rc5/mm/page_alloc.c 2012-08-22 14:25:39.508279046 -0700 > +++ linux/mm/page_alloc.c 2012-09-13 17:06:08.265763526 -0700 > @@ -4456,7 +4456,7 @@ static void __paginginit free_area_init_ > zone->zone_pgdat = pgdat; > > zone_pcp_init(zone); > - lruvec_init(&zone->lruvec, zone); > + lruvec_init(&zone->lruvec); > if (!size) > continue; >