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authorEric Dumazet <dada1@cosmosbay.com>2007-02-10 01:44:48 -0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-02-11 10:51:25 -0800
commit4ba4d4c0c52201009232fe9e781a281054a24e75 (patch)
tree4b4d47c78c561fc8f3d79713e7f80def3d9b73ce
parent0aa5de8590d684274f57647a870851f101bb3543 (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>
-rw-r--r--include/linux/mount.h10
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;
};