Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756982Ab1D0W1e (ORCPT ); Wed, 27 Apr 2011 18:27:34 -0400 Received: from e4.ny.us.ibm.com ([32.97.182.144]:48635 "EHLO e4.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753490Ab1D0W1d (ORCPT ); Wed, 27 Apr 2011 18:27:33 -0400 Date: Wed, 27 Apr 2011 15:27:27 -0700 From: "Paul E. McKenney" To: Thomas Gleixner Cc: Bruno =?iso-8859-1?Q?Pr=E9mont?= , Linus Torvalds , Ingo Molnar , Peter Zijlstra , Mike Frysinger , KOSAKI Motohiro , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, "Paul E. McKenney" , Pekka Enberg Subject: Re: 2.6.39-rc4+: Kernel leaking memory during FS scanning, regression? Message-ID: <20110427222727.GU2135@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20110425214933.GO2468@linux.vnet.ibm.com> <20110426081904.0d2b1494@pluto.restena.lu> <20110426112756.GF4308@linux.vnet.ibm.com> <20110426183859.6ff6279b@neptune.home> <20110426190918.01660ccf@neptune.home> <20110427081501.5ba28155@pluto.restena.lu> <20110427204139.1b0ea23b@neptune.home> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3067 Lines: 76 On Thu, Apr 28, 2011 at 12:06:11AM +0200, Thomas Gleixner wrote: > On Wed, 27 Apr 2011, Bruno Pr?mont wrote: > > On Wed, 27 April 2011 Bruno Pr?mont wrote: > > Voluntary context switches stay constant from the time on SLABs pile up. > > (which makes sense as it doesn't run get CPU slices anymore) > > > > > > Can you please enable CONFIG_SCHED_DEBUG and provide the output of > > > > /proc/sched_stat when the problem surfaces and a minute after the > > > > first snapshot? > > > > hm, did you mean CONFIG_SCHEDSTAT or /proc/sched_debug? > > > > I did use CONFIG_SCHED_DEBUG (and there is no /proc/sched_stat) so I took > > /proc/sched_debug which exists... (attached, taken about 7min and +1min > > after SLABs started piling up), though build processes were SIGSTOPped > > during first minute. > > Oops. /proc/sched_debug is the right thing. > > > printk wrote (in case its timestamp is useful, more below): > > [ 518.480103] sched: RT throttling activated > > Ok. Aside of the fact that the CPU time accounting is completely hosed > this is pointing to the root cause of the problem. > > kthread_rcu seems to run in circles for whatever reason and the RT > throttler catches it. After that things go down the drain completely > as it should get on the CPU again after that 50ms throttling break. Ah. This could happen if there was a huge number of callbacks, in which case blimit would be set very large and kthread_rcu could then go CPU-bound. And this workload was generating large numbers of callbacks due to filesystem operations, right? So, perhaps I should kick kthread_rcu back to SCHED_NORMAL if blimit has been set high. Or have some throttling of my own. I must confess that throttling kthread_rcu for two hours seems a bit harsh. ;-) If this was just throttling kthread_rcu for a few hundred milliseconds, or even for a second or two, things would be just fine. Left to myself, I will put together a patch that puts callback processing down to SCHED_NORMAL in the case where there are huge numbers of callbacks to be processed. > Though we should not ignore the fact, that the RT throttler hit, but > none of the RT tasks actually accumulated runtime. > > So there is a couple of questions: > > - Why does the scheduler detect the 950 ms RT runtime, but does > not accumulate that runtime to any thread > > - Why is the runtime accounting totally hosed > > - Why does that not happen (at least not reproducible) with > TREE_RCU This one I can answer -- In Linus's tree, TREE_RCU still uses softirq, so there is no RCU kthread, so there is nothing to throttle other than ksoftirqd itself. Thanx, Paul > I need some sleep now, but I will try to come up with sensible > debugging tomorrow unless Paul or someone else beats me to it. > > Thanks, > > tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/