From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757475Ab0DAQQR (ORCPT ); Thu, 1 Apr 2010 12:16:17 -0400 Received: from e8.ny.us.ibm.com ([32.97.182.138]:59735 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755565Ab0DAQQI (ORCPT ); Thu, 1 Apr 2010 12:16:08 -0400 Date: Thu, 1 Apr 2010 09:15:51 -0700 From: "Paul E. McKenney" To: Avi Kivity Cc: Peter Zijlstra , Andrea Arcangeli , Thomas Gleixner , Rik van Riel , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Kent Overstreet , Ingo Molnar Subject: Re: [COUNTERPATCH] mm: avoid overflowing preempt_count() in mmu_take_all_locks() Message-ID: <20100401161551.GE2472@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1270117906.1653.139.camel@laptop> <4BB47FC3.1020606@redhat.com> <4BB480CC.2060503@redhat.com> <1270121264.1653.205.camel@laptop> <1270122194.1653.223.camel@laptop> <20100401154249.GQ5825@random.random> <4BB4C0F5.3070204@redhat.com> <1270137406.1598.78.camel@laptop> <4BB4C48C.5000005@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4BB4C48C.5000005@redhat.com> 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 On Thu, Apr 01, 2010 at 07:06:36PM +0300, Avi Kivity wrote: > On 04/01/2010 06:56 PM, Peter Zijlstra wrote: > >On Thu, 2010-04-01 at 18:51 +0300, Avi Kivity wrote: > >>On 04/01/2010 06:42 PM, Andrea Arcangeli wrote: > >>>On Thu, Apr 01, 2010 at 01:43:14PM +0200, Peter Zijlstra wrote: > >>> > >>>>On Thu, 2010-04-01 at 13:27 +0200, Peter Zijlstra wrote: > >>>> > >>>>>I've almost got a patch done that converts those two, still need to look > >>>>>where that tasklist_lock muck happens. > >>>>> > >>>>OK, so the below builds and boots, only need to track down that > >>>>tasklist_lock nesting, but I got to run an errand first. > >>>> > >>>You should have a look at my old patchset where Christoph already > >>>implemented this (and not for decreasing latency but to allow > >>>scheduling in mmu notifier handlers, only needed by XPMEM): > >>> > >>>http://www.kernel.org/pub/linux/kernel/people/andrea/patches/v2.6/2.6.26-rc7/mmu-notifier-v18/ > >>> > >>>The ugliest part of it (that I think you missed below) is the breakage > >>>of the RCU locking in the anon-vma which requires adding refcounting > >>>to it. That was the worst part of the conversion as far as I can tell. > >>> > >>>http://www.kernel.org/pub/linux/kernel/people/andrea/patches/v2.6/2.6.26-rc7/mmu-notifier-v18/anon-vma > >>> > >>Can we use srcu now instead? > >I would much rather we make call_rcu_preempt() available at all times. > > I don't understand. I thought the problem was that the locks were > taken inside an rcu critical section; switching to srcu would fix > that. But how is call_rcu_preempt() related? Grepping a bit, what > is call_rcu_preempt()? my tree doesn't have it. I believe that Peter is referring to the RCU implementation you get with CONFIG_TREE_PREEMPT_RCU, which currently depends on CONFIG_PREEMPT. The other implementation is CONFIG_TREE_RCU, which is usually called "classic RCU". Thanx, Paul