From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753026AbWLORwW (ORCPT ); Fri, 15 Dec 2006 12:52:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753082AbWLORwV (ORCPT ); Fri, 15 Dec 2006 12:52:21 -0500 Received: from pfx2.jmh.fr ([194.153.89.55]:55482 "EHLO pfx2.jmh.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753026AbWLORwV (ORCPT ); Fri, 15 Dec 2006 12:52:21 -0500 From: Eric Dumazet To: Andrew Morton Subject: [PATCH] struct vfsmount : keep mnt_count & mnt_expiry_mark away from mnt_flags Date: Fri, 15 Dec 2006 18:51:58 +0100 User-Agent: KMail/1.9.5 Cc: linux-kernel@vger.kernel.org References: <200612150823.kBF8NV2u011171@shell0.pdx.osdl.net> <20061215083112.GB10687@elte.hu> <20061215081138.4c51e7c5.akpm@osdl.org> In-Reply-To: <20061215081138.4c51e7c5.akpm@osdl.org> MIME-Version: 1.0 Message-Id: <200612151851.58741.dada1@cosmosbay.com> Content-Type: Multipart/Mixed; boundary="Boundary-00=_+CugFmiIRjUXkKj" Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org --Boundary-00=_+CugFmiIRjUXkKj Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline I noticed cache misses in touch_atime() that can be avoided if we keep mnt_count & mnt_expiry_mark in a different cache line than mnt_flags (mostly read) mnt_count & mnt_expiry_mark are modified each time a file is opened/closed in a file system. touch_atime() is called each time a file is read, and generally needs to read mnt_flags. Other fields of struct vfsmount are mostly read so I chose to move mnt_count & mnt_expiry_mark at the end of struct vfsmount. And adding a comment so that nobody tries to re-arrange fields to fill the holes :) On 64bits platforms, the new offsetof(mnt_count) is 0xC0 On 32bits platforms, it is 0x60, so I didnot add a ____cacheline_aligned_in_smp because it would have a too big impact on the size of this object (in particular if CONFIG_X86_L1_CACHE_SHIFT=7) Signed-off-by: Eric Dumazet --Boundary-00=_+CugFmiIRjUXkKj Content-Type: text/plain; charset="iso-8859-1"; name="vfsmount.patch" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="vfsmount.patch" --- linux-2.6.20-rc1-mm1/include/linux/mount.h 2006-12-14 02:14:23.000000000 +0100 +++ linux-2.6.20-rc1-mm1-ed/include/linux/mount.h 2006-12-15 19:30:54.000000000 +0100 @@ -43,9 +43,8 @@ struct vfsmount { struct super_block *mnt_sb; /* pointer to superblock */ struct list_head mnt_mounts; /* list of children, anchored here */ struct list_head mnt_child; /* and going through their mnt_child */ - atomic_t mnt_count; int mnt_flags; - int mnt_expiry_mark; /* true if marked for expiry */ + /* 4 bytes hole on 64bits arches */ char *mnt_devname; /* Name of device e.g. /dev/dsk/hda1 */ struct list_head mnt_list; struct list_head mnt_expire; /* link in fs-specific expiry list */ @@ -54,6 +53,13 @@ struct vfsmount { struct list_head mnt_slave; /* slave list entry */ struct vfsmount *mnt_master; /* slave is on master->mnt_slave_list */ struct mnt_namespace *mnt_ns; /* containing namespace */ + /* + * We put mnt_count & mnt_expiry_mark at the end of struct vfsmount + * to let these frequently modified fields in a separate cache line + * (so that reads of mnt_flags wont ping-pong on SMP machines) + */ + atomic_t mnt_count; + int mnt_expiry_mark; /* true if marked for expiry */ int mnt_pinned; }; --Boundary-00=_+CugFmiIRjUXkKj--