[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, 3 insertions, 3 deletions

diff --git a/fs/freevxfs/vxfs.h b/fs/freevxfs/vxfs.h
index d35979a58743..c8a92652612a 100644
--- a/fs/freevxfs/vxfs.h
+++ b/fs/freevxfs/vxfs.h
@@ -252,7 +252,7 @@ enum {
  * Get filesystem private data from VFS inode.
  */
 #define VXFS_INO(ip) \
-        ((struct vxfs_inode_info *)(ip)->u.generic_ip)
+        ((struct vxfs_inode_info *)(ip)->i_private)
 
 /*
  * Get filesystem private data from VFS superblock.
diff --git a/fs/freevxfs/vxfs_inode.c b/fs/freevxfs/vxfs_inode.c
index ca6a39714771..32a82ed108e4 100644
--- a/fs/freevxfs/vxfs_inode.c
+++ b/fs/freevxfs/vxfs_inode.c
@@ -243,7 +243,7 @@ vxfs_iinit(struct inode *ip, struct vxfs_inode_info *vip)
         ip->i_blocks = vip->vii_blocks;
         ip->i_generation = vip->vii_gen;
 
-        ip->u.generic_ip = (void *)vip;
+        ip->i_private = vip;
         
 }
 
@@ -338,5 +338,5 @@ vxfs_read_inode(struct inode *ip)
 void
 vxfs_clear_inode(struct inode *ip)
 {
-        kmem_cache_free(vxfs_inode_cachep, ip->u.generic_ip);
+        kmem_cache_free(vxfs_inode_cachep, ip->i_private);
 }