Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753528AbaFSEwa (ORCPT ); Thu, 19 Jun 2014 00:52:30 -0400 Received: from mail-wg0-f47.google.com ([74.125.82.47]:63016 "EHLO mail-wg0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751745AbaFSEw3 (ORCPT ); Thu, 19 Jun 2014 00:52:29 -0400 Message-ID: <1403153545.1225.8.camel@edumazet-glaptop2.roam.corp.google.com> Subject: Re: [bisected] pre-3.16 regression on open() scalability From: Eric Dumazet To: Andi Kleen Cc: "Paul E. McKenney" , Dave Hansen , LKML , Josh Triplett , "Chen, Tim C" , Christoph Lameter Date: Wed, 18 Jun 2014 21:52:25 -0700 In-Reply-To: <20140619033816.GQ8178@tassilo.jf.intel.com> References: <20140613224519.GV4581@linux.vnet.ibm.com> <53A0CAE5.9000702@intel.com> <20140618001836.GV4669@linux.vnet.ibm.com> <53A132D4.60408@intel.com> <20140618125831.GB4669@linux.vnet.ibm.com> <53A1CE19.7040103@intel.com> <20140618203052.GT4669@linux.vnet.ibm.com> <20140618235131.GA25946@linux.vnet.ibm.com> <20140619014200.GO8178@tassilo.jf.intel.com> <20140619021337.GA4669@linux.vnet.ibm.com> <20140619033816.GQ8178@tassilo.jf.intel.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2014-06-18 at 20:38 -0700, Andi Kleen wrote: > On Wed, Jun 18, 2014 at 07:13:37PM -0700, Paul E. McKenney wrote: > > On Wed, Jun 18, 2014 at 06:42:00PM -0700, Andi Kleen wrote: > > > > > > I still think it's totally the wrong direction to pollute so > > > many fast paths with this obscure debugging check workaround > > > unconditionally. > > > > OOM prevention should count for something, I would hope. > > OOM in what scenario? This is getting bizarre. > > If something keeps looping forever in the kernel creating > RCU callbacks without any real quiescent states it's simply broken. Typical problem we faced in the past is in exit() path when multi thousands of files/sockets are rcu-freed, and qhimark is hit. Huge latency alerts, as freeing 10000+ items takes a while (about 70 ns per item...) Maybe close_files() should use a cond_resched_and_keep_rcu_queues_small_please() ;) -- 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/