From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752746Ab0ESOPL (ORCPT ); Wed, 19 May 2010 10:15:11 -0400 Received: from mail.openrapids.net ([64.15.138.104]:53715 "EHLO blackscsi.openrapids.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752487Ab0ESOPI (ORCPT ); Wed, 19 May 2010 10:15:08 -0400 Date: Wed, 19 May 2010 10:15:00 -0400 From: Mathieu Desnoyers To: Srikar Dronamraju Cc: Peter Zijlstra , Ingo Molnar , Masami Hiramatsu , Mel Gorman , Steven Rostedt , Randy Dunlap , Linus Torvalds , "H. Peter Anvin" , Roland McGrath , Christoph Hellwig , Ananth N Mavinakayanahalli , Oleg Nesterov , Mark Wielaard , LKML , Jim Keniston , Frederic Weisbecker , "Rafael J. Wysocki" , "Frank Ch. Eigler" , Andrew Morton , "Paul E. McKenney" , Dominique Toupin Subject: Re: [PATCH v4 0/13] Uprobes v4 Message-ID: <20100519141458.GA3961@Krystal> References: <20100518165826.20070.11594.sendpatchset@localhost6.localdomain6> <20100518204944.GA6959@Krystal> <20100519060803.GB19957@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100519060803.GB19957@linux.vnet.ibm.com> X-Editor: vi X-Info: http://www.efficios.com X-Operating-System: Linux/2.6.26-2-686 (i686) X-Uptime: 10:10:56 up 116 days, 16:48, 9 users, load average: 1.37, 1.03, 1.10 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 * Srikar Dronamraju (srikar@linux.vnet.ibm.com) wrote: > > * Srikar Dronamraju (srikar@linux.vnet.ibm.com) wrote: > > > Uprobes Patches > > > > > > Changelog from v3: > > > - Reverted to background page replacement as suggested by Peter Zijlstra. > > > > Why ? > > > > I'm not sure we reached any concensus about the need for a background page > > replacement. > > > > Thanks, > > > > Mathieu > > > > I was tested with access_process_vm(previous patchset) and the current > (background page replacement) and the results are the same. > > However Peter Zijlstra's contention still stands that we might be > relying on a undocumented feature in the hardware The access_process_vm scheme is in many ways similar to what kprobes has been doing for years. So I would not rely on that as a primary argument against the access_process_vm approach. > and the flipping the > pages isnt that hard or expensive. > > Even Linus, (http://lkml.org/lkml/2010/1/27/87) had shown inclination > towards background page replacement. > > Also when uprobes implements global tracing support (i.e probing a > particular symbol in a dso across processes), it has to rely on > background page replacement. Ah OK. If you have to use page replacement for global tracing, I see that as a good argument for using page replacement everywhere. > > Hence I based this patchset on background page replacement rather than > on access_process_vm. Later On, if there is a consensus on using > access_process_vm, we can make the corresponding changes. Well, page replacement seems like a good way to support global tracing, so I doubt that we'll ever revert back to access_process_vm. Thanks, Mathieu > > -- > Thanks and Regards > Srikar -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com