Lookup typically touches three fields of the dentry: d_bucket, d_name.hash and
d_parent.
Change the layout of things so that these will always be in the same
cacheline.
---
25-akpm/include/linux/dcache.h | 19 +++++++++++++++----
1 files changed, 15 insertions(+), 4 deletions(-)
diff -puN include/linux/dcache.h~dentry-layout-tweaks include/linux/dcache.h
--- 25/include/linux/dcache.h~dentry-layout-tweaks 2004-05-08 21:51:36.024307400 -0700
+++ 25-akpm/include/linux/dcache.h 2004-05-08 21:51:36.029306640 -0700
@@ -27,11 +27,14 @@ struct vfsmount;
/*
* "quick string" -- eases parameter passing, but more importantly
* saves "metadata" about the string (ie length and the hash).
+ *
+ * hash comes first so it snuggles against d_parent and d_bucket in the
+ * dentry.
*/
struct qstr {
+ unsigned int hash;
const unsigned char *name;
unsigned int len;
- unsigned int hash;
};
struct dentry_stat_t {
@@ -75,12 +78,23 @@ full_name_hash(const unsigned char *name
struct dcookie_struct;
+/*
+ * On x86, dentries are a multiple of 16 bytes, with 16-byte alignment.
+ */
struct dentry {
atomic_t d_count;
unsigned int d_flags; /* protected by d_lock */
spinlock_t d_lock; /* per dentry lock */
struct inode *d_inode; /* Where the name belongs to - NULL is
* negative */
+ /*
+ * The next three fields are touched by __d_lookup. Place them here
+ * so they all fit in a 16-byte range, with 16-byte alignment.
+ */
+ struct dentry *d_parent; /* parent directory */
+ struct hlist_head *d_bucket; /* lookup hash bucket */
+ struct qstr d_name;
+
struct list_head d_lru; /* LRU list */
struct list_head d_child; /* child of parent list */
struct list_head d_subdirs; /* our children */
@@ -92,10 +106,7 @@ struct dentry {
void *d_fsdata; /* fs-specific data */
struct rcu_head d_rcu;
struct dcookie_struct *d_cookie; /* cookie, if any */
- struct dentry *d_parent; /* parent directory */
- struct qstr d_name;
struct hlist_node d_hash; /* lookup hash list */
- struct hlist_head *d_bucket; /* lookup hash bucket */
unsigned char d_iname[0]; /* small names */
};
_