From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753788AbXLBHtg (ORCPT ); Sun, 2 Dec 2007 02:49:36 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751716AbXLBHt2 (ORCPT ); Sun, 2 Dec 2007 02:49:28 -0500 Received: from cantor.suse.de ([195.135.220.2]:54042 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751644AbXLBHt1 (ORCPT ); Sun, 2 Dec 2007 02:49:27 -0500 Date: Sat, 1 Dec 2007 23:54:37 -0800 From: Greg KH To: rae l Cc: linux-kernel@vger.kernel.org, ebiederm@xmission.com Subject: Re: Since sysfs_mount is static and used only in sysfs_init function, it could be just an automatic variable. Message-ID: <20071202075437.GA19897@suse.de> References: <91b13c310712011231k3604214bx3559387c568cce09@mail.gmail.com> <20071202044825.GA7004@suse.de> <91b13c310712012252k5307735x782582fd2d7abd94@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <91b13c310712012252k5307735x782582fd2d7abd94@mail.gmail.com> User-Agent: Mutt/1.5.16 (2007-06-09) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Dec 02, 2007 at 02:52:17PM +0800, rae l wrote: > On Dec 2, 2007 12:48 PM, Greg KH wrote: > ... > > > and where is a detailed explaination on kern_mount? could someone give > > > some comments or documentation pointers on this? > > > > See the patches that Eric Biederman just posted to lkml for why this > > structure is a static pointer this way right now, it's in preparation > > for future patches. > I have checked commit 7d0c7d676cc066413e1583b5af9fba8011972d41 by Eric > W. Biederman, > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=7d0c7d676cc066413e1583b5af9fba8011972d41 > > which just make sysfs_mount from externally visible to static that > could be only used in one c file, > > but I mean that the static variable is still on kernel bss section, > this consumes a pointer (4 or 8 bytes) memory, > > through a grep from fs/sysfs/, it appears that the variable > sysfs_mount is only used in the sysfs_init function, > > $ grep -RsInw sysfs_mount fs/sysfs/ > fs/sysfs/mount.c:25:static struct vfsmount *sysfs_mount; > fs/sysfs/mount.c:101: sysfs_mount = kern_mount(&sysfs_fs_type); > fs/sysfs/mount.c:102: if (IS_ERR(sysfs_mount)) { > fs/sysfs/mount.c:104: err = PTR_ERR(sysfs_mount); > fs/sysfs/mount.c:105: sysfs_mount = NULL; > > we could mark this variable an automatic one, which scope is just in > this function, thus created and destroyed with the stack, > this approach does not consume a pointer on kernel bss section, > > Why not do this? Again, see the patches he _just_ posted to lkml, the specific message you are looking for is: Message-ID: Subject: [PATCH 01/10] sysfs: Make sysfs_mount static again. Also see the whole long thread for more details. If you have further questions about this, please ask Eric. thanks, greg k-h