From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752503AbYIWSNf (ORCPT ); Tue, 23 Sep 2008 14:13:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754100AbYIWSNV (ORCPT ); Tue, 23 Sep 2008 14:13:21 -0400 Received: from tomts20.bellnexxia.net ([209.226.175.74]:47987 "EHLO tomts20-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753993AbYIWSNU (ORCPT ); Tue, 23 Sep 2008 14:13:20 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AgsFANzJ2EhMQWq+/2dsb2JhbACBXrcXgWc Date: Tue, 23 Sep 2008 14:13:13 -0400 From: Mathieu Desnoyers To: Peter Zijlstra Cc: Tom Zanussi , prasad@linux.vnet.ibm.com, Martin Bligh , Linux Kernel Mailing List , Linus Torvalds , Thomas Gleixner , Steven Rostedt , od@novell.com, "Frank Ch. Eigler" , Andrew Morton , hch@lst.de, David Wilder , Christoph Lameter , linux-mm@kvack.org Subject: Re: Unified tracing buffer Message-ID: <20080923181313.GA4947@Krystal> References: <33307c790809191433w246c0283l55a57c196664ce77@mail.gmail.com> <1221869279.8359.31.camel@lappy.programming.kicks-ass.net> <20080922140740.GB5279@in.ibm.com> <1222094724.16700.11.camel@lappy.programming.kicks-ass.net> <1222147545.6875.135.camel@charm-linux> <1222162270.16700.57.camel@lappy.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <1222162270.16700.57.camel@lappy.programming.kicks-ass.net> X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.21.3-grsec (i686) X-Uptime: 14:03:24 up 110 days, 22:43, 8 users, load average: 1.06, 0.89, 0.74 User-Agent: Mutt/1.5.16 (2007-06-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Peter Zijlstra (a.p.zijlstra@chello.nl) wrote: > On Tue, 2008-09-23 at 00:25 -0500, Tom Zanussi wrote: > > > - get rid of anything having to do with padding, nobody needs it and its > > only affect has been to horribly distort and complicate a lot of the > > code > > - get rid of sub-buffers, they just cause confusion > > - get rid of mmap, nobody uses it > > - no sub-buffers and no mmap support means we can get rid of most of the > > callbacks, and a lot of API confusion along with them > > - add relay flags - they probably should have been used from the > > beginning and options made explicit instead of being shoehorned into the > > callback functions. > > - get rid of the vmap buffers as they cause tlb pressure and eat up > precious vspace on 32 bit platforms. > Although I agree on the basic idea, namely to use a sane amount of TLB entries for tracing, I disagree on the way proposed to reach this goal. Such memory management concerns belong to the mm field and should not be done "oh so cleverly" by a buffer management infrastructure in the back of the kernel memory management infrastructure. I think we should instead try to figure out what is currently missing in the kernel vmap mechanism (probably the ability to vmap from large 4MB pages after boot), and fix _that_ instead (if possible), which would not only benefit to tracing, but also to module support. Also, I would like to keep a contiguous address mapping within buffers so we could keep the buffer read/write code as simple as possible, leveraging the existing CPU MM unit. I added Christoph Lameter to the CC list, he always comes with clever ideas. :) Mathieu -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68