Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753626Ab3JAPmA (ORCPT ); Tue, 1 Oct 2013 11:42:00 -0400 Received: from mx1.redhat.com ([209.132.183.28]:64365 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753347Ab3JAPl6 (ORCPT ); Tue, 1 Oct 2013 11:41:58 -0400 Date: Tue, 1 Oct 2013 17:34:52 +0200 From: Oleg Nesterov To: "Paul E. McKenney" Cc: Peter Zijlstra , Mel Gorman , Rik van Riel , Srikar Dronamraju , Ingo Molnar , Andrea Arcangeli , Johannes Weiner , Linux-MM , LKML , Thomas Gleixner , Steven Rostedt Subject: Re: [PATCH] hotplug: Optimize {get,put}_online_cpus() Message-ID: <20131001153451.GB3515@redhat.com> References: <20130926111042.GS3081@twins.programming.kicks-ass.net> <20130926165840.GA863@redhat.com> <20130926175016.GI3657@laptop.programming.kicks-ass.net> <20130927181532.GA8401@redhat.com> <20130927204116.GJ15690@laptop.programming.kicks-ass.net> <20131001035604.GW19582@linux.vnet.ibm.com> <20131001141429.GA32423@redhat.com> <20131001144537.GC5790@linux.vnet.ibm.com> <20131001144820.GP3657@laptop.programming.kicks-ass.net> <20131001152449.GD5790@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131001152449.GD5790@linux.vnet.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 908 Lines: 25 On 10/01, Paul E. McKenney wrote: > > On Tue, Oct 01, 2013 at 04:48:20PM +0200, Peter Zijlstra wrote: > > On Tue, Oct 01, 2013 at 07:45:37AM -0700, Paul E. McKenney wrote: > > > If you don't have cpuhp_seq, you need some other way to avoid > > > counter overflow. Which might be provided by limited number of > > > tasks, or, on 64-bit systems, 64-bit counters. > > > > How so? PID space is basically limited to 30 bits, so how could we > > overflow a 32bit reference counter? > > Nesting. Still it seems that UINT_MAX / PID_MAX_LIMIT has enough room. But again, OK lets make it ulong. The question is, how cpuhp_seq can help and why we can't kill it. Oleg. -- 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/