[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, 1 insertions, 1 deletions

diff --git a/fs/inode.c b/fs/inode.c
index 0bf9f0444a96..77e254792025 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -163,7 +163,7 @@ static struct inode *alloc_inode(struct super_block *sb)
                                 bdi = sb->s_bdev->bd_inode->i_mapping->backing_dev_info;
                         mapping->backing_dev_info = bdi;
                 }
-                memset(&inode->u, 0, sizeof(inode->u));
+                inode->i_private = 0;
                 inode->i_mapping = mapping;
         }
         return inode;