[PATCH] inode_diet: Replace inode.u.generic_ip with inode.i_private

The following patches reduce the size of the VFS inode structure by 28 bytes
on a UP x86.  (It would be more on an x86_64 system).  This is a 10% reduction
in the inode size on a UP kernel that is configured in a production mode
(i.e., with no spinlock or other debugging functions enabled; if you want to
save memory taken up by in-core inodes, the first thing you should do is
disable the debugging options; they are responsible for a huge amount of bloat
in the VFS inode structure).

This patch:

The filesystem or device-specific pointer in the inode is inside a union,
which is pretty pointless given that all 30+ users of this field have been
using the void pointer.  Get rid of the union and rename it to i_private, with
a comment to explain who is allowed to use the void pointer.  This is just a
cleanup, but it allows us to reuse the union 'u' for something something where
the union will actually be used.

[judith@osdl.org: powerpc build fix]
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Judith Lebzelter <judith@osdl.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index 34ebbc1..6759b98 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -517,7 +517,7 @@ static struct inode *bm_get_inode(struct super_block *sb, int mode)
 
 static void bm_clear_inode(struct inode *inode)
 {
-	kfree(inode->u.generic_ip);
+	kfree(inode->i_private);
 }
 
 static void kill_node(Node *e)
@@ -545,7 +545,7 @@ static void kill_node(Node *e)
 static ssize_t
 bm_entry_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
 {
-	Node *e = file->f_dentry->d_inode->u.generic_ip;
+	Node *e = file->f_dentry->d_inode->i_private;
 	loff_t pos = *ppos;
 	ssize_t res;
 	char *page;
@@ -579,7 +579,7 @@ static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
 				size_t count, loff_t *ppos)
 {
 	struct dentry *root;
-	Node *e = file->f_dentry->d_inode->u.generic_ip;
+	Node *e = file->f_dentry->d_inode->i_private;
 	int res = parse_command(buffer, count);
 
 	switch (res) {
@@ -646,7 +646,7 @@ static ssize_t bm_register_write(struct file *file, const char __user *buffer,
 	}
 
 	e->dentry = dget(dentry);
-	inode->u.generic_ip = e;
+	inode->i_private = e;
 	inode->i_fop = &bm_entry_operations;
 
 	d_instantiate(dentry, inode);