From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758946Ab2INPqn (ORCPT ); Fri, 14 Sep 2012 11:46:43 -0400 Received: from zene.cmpxchg.org ([85.214.230.12]:57602 "EHLO zene.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758736Ab2INPqk (ORCPT ); Fri, 14 Sep 2012 11:46:40 -0400 Date: Fri, 14 Sep 2012 11:46:25 -0400 From: Johannes Weiner To: Hugh Dickins Cc: 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 , Konstantin Khlebnikov , paul.gortmaker@windriver.com Subject: Re: [PATCH] memory cgroup: update root memory cgroup when node is onlined Message-ID: <20120914154625.GN1560@cmpxchg.org> References: <505187D4.7070404@cn.fujitsu.com> <20120913205935.GK1560@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 13, 2012 at 06:36:34PM -0700, 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 :( We would not want that! > > 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. Ok, you certainly have a point. > > 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 This looks good to me, thanks. Acked-by: Johannes Weiner