From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754784Ab2JPHVj (ORCPT ); Tue, 16 Oct 2012 03:21:39 -0400 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:57227 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754389Ab2JPHVg (ORCPT ); Tue, 16 Oct 2012 03:21:36 -0400 X-SecurityPolicyCheck: OK by SHieldMailChecker v1.8.4 Message-ID: <507D0AE2.1020604@jp.fujitsu.com> Date: Tue, 16 Oct 2012 16:21:06 +0900 From: Kamezawa Hiroyuki User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:16.0) Gecko/20121010 Thunderbird/16.0.1 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, Andrew Morton , Konstantin Khlebnikov , 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 (2012/09/14 10:36), 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 :( > >> 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 Acked-by: KAMEZAWA Hiroyuki