Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161011AbcK3LKQ (ORCPT ); Wed, 30 Nov 2016 06:10:16 -0500 Received: from mail-wj0-f196.google.com ([209.85.210.196]:32911 "EHLO mail-wj0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933901AbcK3LJ4 (ORCPT ); Wed, 30 Nov 2016 06:09:56 -0500 Date: Wed, 30 Nov 2016 12:09:44 +0100 From: Michal Hocko To: Donald Buczek Cc: Paul Menzel , dvteam@molgen.mpg.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Josh Triplett , "Paul E. McKenney" Subject: Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Message-ID: <20161130110944.GD18432@dhcp22.suse.cz> References: <20161121134130.GB18112@dhcp22.suse.cz> <20161121140122.GU3612@linux.vnet.ibm.com> <20161121141818.GD18112@dhcp22.suse.cz> <20161121142901.GV3612@linux.vnet.ibm.com> <68025f6c-6801-ab46-b0fc-a9407353d8ce@molgen.mpg.de> <20161124101525.GB20668@dhcp22.suse.cz> <583AA50A.9010608@molgen.mpg.de> <20161128110449.GK14788@dhcp22.suse.cz> <109d5128-f3a4-4b6e-db17-7a1fcb953500@molgen.mpg.de> <29196f89-c35e-f79d-8e4d-2bf73fe930df@molgen.mpg.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <29196f89-c35e-f79d-8e4d-2bf73fe930df@molgen.mpg.de> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1003 Lines: 33 [CCing Paul] On Wed 30-11-16 11:28:34, Donald Buczek wrote: [...] > shrink_active_list gets and releases the spinlock and calls cond_resched(). > This should give other tasks a chance to run. Just as an experiment, I'm > trying > > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1921,7 +1921,7 @@ static void shrink_active_list(unsigned long > nr_to_scan, > spin_unlock_irq(&pgdat->lru_lock); > > while (!list_empty(&l_hold)) { > - cond_resched(); > + cond_resched_rcu_qs(); > page = lru_to_page(&l_hold); > list_del(&page->lru); > > and didn't hit a rcu_sched warning for >21 hours uptime now. We'll see. This is really interesting! Is it possible that the RCU stall detector is somehow confused? > Is preemption disabled for another reason? I do not think so. I will have to double check the code but this is a standard sleepable context. Just wondering what is the PREEMPT configuration here? -- Michal Hocko SUSE Labs