diff options
| author | Eric Dumazet <dada1@cosmosbay.com> | 2007-02-10 01:44:48 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2007-02-11 10:51:25 -0800 |
| commit | 4ba4d4c0c52201009232fe9e781a281054a24e75 (patch) | |
| tree | 4b4d47c78c561fc8f3d79713e7f80def3d9b73ce /include/linux | |
| parent | 0aa5de8590d684274f57647a870851f101bb3543 (diff) | |
[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 <dada1@cosmosbay.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/mount.h | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/include/linux/mount.h b/include/linux/mount.h index 1b7e178b0d8..dab69afee2f 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; }; |