[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>

2 files changed, 4 insertions, 4 deletions

diff --git a/arch/s390/hypfs/inode.c b/arch/s390/hypfs/inode.c
index bdade5f2e325..8735024d235b 100644
--- a/arch/s390/hypfs/inode.c
+++ b/arch/s390/hypfs/inode.c
@@ -104,13 +104,13 @@ static struct inode *hypfs_make_inode(struct super_block *sb, int mode)
 
 static void hypfs_drop_inode(struct inode *inode)
 {
-        kfree(inode->u.generic_ip);
+        kfree(inode->i_private);
         generic_delete_inode(inode);
 }
 
 static int hypfs_open(struct inode *inode, struct file *filp)
 {
-        char *data = filp->f_dentry->d_inode->u.generic_ip;
+        char *data = filp->f_dentry->d_inode->i_private;
         struct hypfs_sb_info *fs_info;
 
         if (filp->f_mode & FMODE_WRITE) {
@@ -352,7 +352,7 @@ static struct dentry *hypfs_create_file(struct super_block *sb,
                 parent->d_inode->i_nlink++;
         } else
                 BUG();
-        inode->u.generic_ip = data;
+        inode->i_private = data;
         d_instantiate(dentry, inode);
         dget(dentry);
         return dentry;
diff --git a/arch/s390/kernel/debug.c b/arch/s390/kernel/debug.c
index 7ba20922a535..43f3d0c7e132 100644
--- a/arch/s390/kernel/debug.c
+++ b/arch/s390/kernel/debug.c
@@ -603,7 +603,7 @@ debug_open(struct inode *inode, struct file *file)
         debug_info_t *debug_info, *debug_info_snapshot;
 
         down(&debug_lock);
-        debug_info = (struct debug_info*)file->f_dentry->d_inode->u.generic_ip;
+        debug_info = file->f_dentry->d_inode->i_private;
         /* find debug view */
         for (i = 0; i < DEBUG_MAX_VIEWS; i++) {
                 if (!debug_info->views[i])