From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752309AbZEJFeP (ORCPT ); Sun, 10 May 2009 01:34:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752519AbZEJFd7 (ORCPT ); Sun, 10 May 2009 01:33:59 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:50292 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751699AbZEJFd6 (ORCPT ); Sun, 10 May 2009 01:33:58 -0400 Date: Sat, 9 May 2009 22:26:12 -0700 From: Andrew Morton To: Ingo Molnar Cc: fengguang.wu@intel.com, fweisbec@gmail.com, rostedt@goodmis.org, a.p.zijlstra@chello.nl, lizf@cn.fujitsu.com, linux-kernel@vger.kernel.org, kosaki.motohiro@jp.fujitsu.com, andi@firstfloor.org, mpm@selenic.com, adobriyan@gmail.com, linux-mm@kvack.org Subject: Re: [PATCH 4/8] proc: export more page flags in /proc/kpageflags Message-Id: <20090509222612.887b96e3.akpm@linux-foundation.org> In-Reply-To: <20090509104409.GB16138@elte.hu> References: <20090508105320.316173813@intel.com> <20090508111031.020574236@intel.com> <20090508114742.GB17129@elte.hu> <20090508132452.bafa287a.akpm@linux-foundation.org> <20090509104409.GB16138@elte.hu> X-Mailer: Sylpheed 2.4.8 (GTK+ 2.12.5; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 9 May 2009 12:44:09 +0200 Ingo Molnar wrote: > And because it was so crappy to be in /proc we are now also > treating it as a hard ABI, not as a debugfs interface - for that > single app that is using it. We'd probably make better progress here were someone to explain what pagemap actually is. pagemap is a userspace interface via which application developers (including embedded) can analyse, understand and optimise their use of memory. It is not debugging feature at all, let alone a kernel debugging feature. For this reason it is not appropriate that its interfaces be presented in debugfs. Furthermore the main control file for pagemap is in /proc//pagemap. pagemap _cannot_ be put in debugfs because debugfs doesn't maintain the per-process subdirectories in which to place it. /proc// is exactly the place where the pagemap file should appear. Yes, we could place pagemap's two auxiliary files into debugfs but it would be rather stupid to split the feature's control files across two pseudo filesystems, one of which may not even exist. Plus pagemap is not a kernel debugging feature.