From 4ba4d4c0c52201009232fe9e781a281054a24e75 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Sat, 10 Feb 2007 01:44:48 -0800 Subject: [PATCH] [PATCH] struct vfsmount: keep mnt_count & mnt_expiry_mark away from mnt_flags 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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/mount.h | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/include/linux/mount.h b/include/linux/mount.h index 1b7e178b0d..dab69afee2 100644 --- a/include/linux/mount.h +++ b/include/linux/mount.h @@ -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; }; -- 2.39.5