Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752058Ab1CPHwu (ORCPT ); Wed, 16 Mar 2011 03:52:50 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:47791 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751877Ab1CPHwo (ORCPT ); Wed, 16 Mar 2011 03:52:44 -0400 Subject: Re: [PATCH v2 2.6.38-rc8-tip 4/20] 4: uprobes: Adding and remove a uprobe in a rb tree. From: Peter Zijlstra To: Eric Dumazet Cc: Thomas Gleixner , Srikar Dronamraju , Ingo Molnar , Steven Rostedt , Linux-mm , Arnaldo Carvalho de Melo , Linus Torvalds , Masami Hiramatsu , Christoph Hellwig , Ananth N Mavinakayanahalli , Andi Kleen , Oleg Nesterov , Andrew Morton , Jim Keniston , Roland McGrath , SystemTap , LKML , "Paul E. McKenney" In-Reply-To: <1300228944.2565.19.camel@edumazet-laptop> References: <20110314133403.27435.7901.sendpatchset@localhost6.localdomain6> <20110314133444.27435.50684.sendpatchset@localhost6.localdomain6> <20110315173041.GB24254@linux.vnet.ibm.com> <1300218499.2250.12.camel@laptop> <1300228944.2565.19.camel@edumazet-laptop> Content-Type: text/plain; charset="UTF-8" Date: Wed, 16 Mar 2011 08:54:27 +0100 Message-ID: <1300262067.2250.49.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1711 Lines: 45 On Tue, 2011-03-15 at 23:42 +0100, Eric Dumazet wrote: > Le mardi 15 mars 2011 à 20:48 +0100, Peter Zijlstra a écrit : > > On Tue, 2011-03-15 at 20:22 +0100, Thomas Gleixner wrote: > > > I am not sure if its a good idea to walk the tree > > > > as and when the tree is changing either because of a insertion or > > > > deletion of a probe. > > > > > > I know that you cannot walk the tree lockless except you would use > > > some rcu based container for your probes. > > > > You can in fact combine a seqlock, rb-trees and RCU to do lockless > > walks. > > > > https://lkml.org/lkml/2010/10/20/160 > > > > and > > > > https://lkml.org/lkml/2010/10/20/437 > > > > But doing that would be an optimization best done once we get all this > > working nicely. > > > > We have such schem in net/ipv4/inetpeer.c function inet_getpeer() (using > a seqlock on latest net-next-2.6 tree), but we added a counter to make > sure a reader could not enter an infinite loop while traversing tree Right, Linus suggested a single lockless iteration, but a limited count works too. > (AVL tree in inetpeer case). Ooh, there's an AVL implementation in the kernel? I have to ask, why not use the RB-tree? (I know AVL has a slightly stronger balancing condition which reduces the max depth from 2*log(n) to 1+log(n)). Also, if it does make sense to have both and AVL and RB implementation, does it then also make sense to lift the AVL thing to generic code into lib/ ? -- 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/