[PATCH] reduce size of struct dentry on 64bit

[Anton Blanchard]

Reduce size of struct dentry from 248 to 232 bytes on 64bit.

- Reduce size of qstr by 8 bytes, placing int hash and int len together.
  We gain a further 4 byte saving when qstr is used in struct dentry
  since qstr goes from 24 to 16 bytes and the next member (d_lru)
  requires 8 byte alignment (which means 4 bytes of padding).
  
- Move d_mounted to the end, since char d_iname[] only requires 1 byte
  alignment. This reduces struct dentry by another 4 bytes.

With these changes the number of objects we can fit into a 4kB slab
goes from 16 to 17 on ppc64.

Note the above assumes the architecture naturally aligns types.

Signed-off-by: Anton Blanchard <anton@xxxxxxxxx>

diff -puN include/linux/dcache.h~optimize_structs include/linux/dcache.h
--- gr_work/include/linux/dcache.h~optimize_structs	2004-08-14 10:51:08.700491559 -0500
+++ gr_work-anton/include/linux/dcache.h	2004-08-14 10:51:08.718488705 -0500
@@ -33,8 +33,8 @@ struct vfsmount;
  */
 struct qstr {
 	unsigned int hash;
-	const unsigned char *name;
 	unsigned int len;
+	const unsigned char *name;
 };
 
 struct dentry_stat_t {
@@ -101,11 +101,11 @@ struct dentry {
 	unsigned long d_time;		/* used by d_revalidate */
 	struct dentry_operations *d_op;
 	struct super_block *d_sb;	/* The root of the dentry tree */
-	int d_mounted;
 	void *d_fsdata;			/* fs-specific data */
  	struct rcu_head d_rcu;
 	struct dcookie_struct *d_cookie; /* cookie, if any */
 	struct hlist_node d_hash;	/* lookup hash list */	
+	int d_mounted;
 	unsigned char d_iname[DNAME_INLINE_LEN_MIN];	/* small names */
 };
 
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