From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752120AbXKSS6R (ORCPT ); Mon, 19 Nov 2007 13:58:17 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751509AbXKSS6D (ORCPT ); Mon, 19 Nov 2007 13:58:03 -0500 Received: from tomts22-srv.bellnexxia.net ([209.226.175.184]:38406 "EHLO tomts22-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751053AbXKSS6B (ORCPT ); Mon, 19 Nov 2007 13:58:01 -0500 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: Ah4FAA5rQUdMROHU/2dsb2JhbACBWA Date: Mon, 19 Nov 2007 13:52:58 -0500 From: Mathieu Desnoyers To: Dave Hansen Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mbligh@google.com Subject: Re: [RFC 5/7] LTTng instrumentation mm Message-ID: <20071119185258.GA998@Krystal> References: <20071113193349.214098508@polymtl.ca> <20071113194025.150641834@polymtl.ca> <1195160783.7078.203.camel@localhost> <20071115215142.GA7825@Krystal> <1195164977.27759.10.camel@localhost> <20071116144742.GA17255@Krystal> <1195495626.27759.119.camel@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <1195495626.27759.119.camel@localhost> X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.21.3-grsec (i686) X-Uptime: 13:50:10 up 15 days, 23:55, 5 users, load average: 0.91, 1.97, 2.10 User-Agent: Mutt/1.5.16 (2007-06-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Dave Hansen (haveblue@us.ibm.com) wrote: > On Fri, 2007-11-16 at 09:47 -0500, Mathieu Desnoyers wrote: > > * Dave Hansen (haveblue@us.ibm.com) wrote: > > > For most (all?) architectures, the PFN and the virtual address in the > > > kernel's linear are interchangeable with pretty trivial arithmetic. All > > > pages have a pfn, but not all have a virtual address. Thus, I suggested > > > using the pfn. What kind of virtual addresses are you talking about? > > > > > > > Hrm, in asm-generic/memory_model.h, we have various versions of > > __page_to_pfn. Normally they all cast the result to (unsigned long), > > except for : > > > > > > #elif defined(CONFIG_SPARSEMEM_VMEMMAP) > > > > /* memmap is virtually contigious. */ > > #define __pfn_to_page(pfn) (vmemmap + (pfn)) > > #define __page_to_pfn(page) ((page) - vmemmap) > > > > So I guess the result is a pointer ? Should this be expected ? > > Nope. 'pointer - pointer' is an integer. Just solve this equation for > integer: > > 'pointer + integer = pointer' > Well, using page_to_pfn turns out to be ugly in markers (and in printks) then. Depending on the architecture, it will result in either an unsigned long (x86_64) or an unsigned int (i386), which corresponds to %lu or %u and will print a warning if we don't cast it explicitly. Mathieu > -- Dave > -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68