From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f70.google.com (mail-wm0-f70.google.com [74.125.82.70]) by kanga.kvack.org (Postfix) with ESMTP id 161F26B0274 for ; Wed, 30 Nov 2016 12:24:01 -0500 (EST) Received: by mail-wm0-f70.google.com with SMTP id g23so52209299wme.4 for ; Wed, 30 Nov 2016 09:24:01 -0800 (PST) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id l66si8051503wml.44.2016.11.30.09.23.59 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 30 Nov 2016 09:23:59 -0800 (PST) Received: from pps.filterd (m0098413.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.17/8.16.0.17) with SMTP id uAUHNg8Q039759 for ; Wed, 30 Nov 2016 12:23:58 -0500 Received: from e37.co.us.ibm.com (e37.co.us.ibm.com [32.97.110.158]) by mx0b-001b2d01.pphosted.com with ESMTP id 2722bs2xu4-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 30 Nov 2016 12:23:58 -0500 Received: from localhost by e37.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 30 Nov 2016 10:23:57 -0700 Date: Wed, 30 Nov 2016 09:23:55 -0800 From: "Paul E. McKenney" Subject: Re: INFO: rcu_sched detected stalls on CPUs/tasks with `kswapd` and `mem_cgroup_shrink_node` Reply-To: paulmck@linux.vnet.ibm.com References: <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> <20161130110944.GD18432@dhcp22.suse.cz> <20161130115320.GO3924@linux.vnet.ibm.com> <20161130131910.GF18432@dhcp22.suse.cz> <20161130142955.GS3924@linux.vnet.ibm.com> <20161130163820.GQ3092@twins.programming.kicks-ass.net> <20161130170557.GK18432@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161130170557.GK18432@dhcp22.suse.cz> Message-Id: <20161130172355.GA3924@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Peter Zijlstra , Donald Buczek , Paul Menzel , dvteam@molgen.mpg.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Josh Triplett On Wed, Nov 30, 2016 at 06:05:57PM +0100, Michal Hocko wrote: > On Wed 30-11-16 17:38:20, Peter Zijlstra wrote: > > On Wed, Nov 30, 2016 at 06:29:55AM -0800, Paul E. McKenney wrote: > > > We can, and you are correct that cond_resched() does not unconditionally > > > supply RCU quiescent states, and never has. Last time I tried to add > > > cond_resched_rcu_qs() semantics to cond_resched(), I got told "no", > > > but perhaps it is time to try again. > > > > Well, you got told: "ARRGH my benchmark goes all regress", or something > > along those lines. Didn't we recently dig out those commits for some > > reason or other? > > > > Finding out what benchmark that was and running it against this patch > > would make sense. > > > > Also, I seem to have missed, why are we going through this again? > > Well, the point I've brought that up is because having basically two > APIs for cond_resched is more than confusing. Basically all longer in > kernel loops do cond_resched() but it seems that this will not help the > silence RCU lockup detector in rare cases where nothing really wants to > schedule. I am really not sure whether we want to sprinkle > cond_resched_rcu_qs at random places just to silence RCU detector... Just in case there is any doubt on this point, any patch of mine adding cond_resched_rcu_qs() functionality to cond_resched() cannot go upstream without Peter's Acked-by. Or did you have some other solution in mind? Thanx, Paul -- 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