From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-f176.google.com (mail-we0-f176.google.com [74.125.82.176]) by kanga.kvack.org (Postfix) with ESMTP id ADCC06B0031 for ; Fri, 7 Feb 2014 08:45:35 -0500 (EST) Received: by mail-we0-f176.google.com with SMTP id q58so2325716wes.35 for ; Fri, 07 Feb 2014 05:45:35 -0800 (PST) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id hk7si2321125wjb.30.2014.02.07.05.45.33 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Fri, 07 Feb 2014 05:45:33 -0800 (PST) Date: Fri, 7 Feb 2014 14:45:33 +0100 From: Michal Hocko Subject: Re: [PATCH] cgroup: use an ordered workqueue for cgroup destruction Message-ID: <20140207134533.GC5121@dhcp22.suse.cz> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: Tejun Heo , Filipe Brandenburger , Li Zefan , Andrew Morton , Johannes Weiner , Greg Thelen , Michel Lespinasse , Markus Blank-Burian , Shawn Bohrer , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org On Thu 06-02-14 15:56:01, Hugh Dickins wrote: > Sometimes the cleanup after memcg hierarchy testing gets stuck in > mem_cgroup_reparent_charges(), unable to bring non-kmem usage down to 0. > > There may turn out to be several causes, but a major cause is this: the > workitem to offline parent can get run before workitem to offline child; > parent's mem_cgroup_reparent_charges() circles around waiting for the > child's pages to be reparented to its lrus, but it's holding cgroup_mutex > which prevents the child from reaching its mem_cgroup_reparent_charges(). > > Just use an ordered workqueue for cgroup_destroy_wq. Hmm, interesting. Markus has seen hangs even with mem_cgroup_css_offline and the referenced cgroup fixes, maybe this is the the right one finally. > Fixes: e5fca243abae ("cgroup: use a dedicated workqueue for cgroup destruction") > Suggested-by: Filipe Brandenburger > Signed-off-by: Hugh Dickins > Cc: stable@vger.kernel.org # 3.10+ Reviewed-by: Michal Hocko e5fca243abae was marked for 3.9 stable but I do not see it in the Greg's 3.9 stable branch so 3.10+ seems to be sufficient. > --- > > kernel/cgroup.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > --- 3.14-rc1/kernel/cgroup.c 2014-02-02 18:49:07.737302111 -0800 > +++ linux/kernel/cgroup.c 2014-02-06 15:20:35.548904965 -0800 > @@ -4845,12 +4845,12 @@ static int __init cgroup_wq_init(void) > /* > * There isn't much point in executing destruction path in > * parallel. Good chunk is serialized with cgroup_mutex anyway. > - * Use 1 for @max_active. > + * Must be ordered to make sure parent is offlined after children. > * > * We would prefer to do this in cgroup_init() above, but that > * is called before init_workqueues(): so leave this until after. > */ > - cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1); > + cgroup_destroy_wq = alloc_ordered_workqueue("cgroup_destroy", 0); > BUG_ON(!cgroup_destroy_wq); > > /* -- Michal Hocko SUSE Labs -- 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