[PATCH] reduce sizeof(struct file)

Now that RCU applied on 'struct file' seems stable, we can place f_rcuhead
in a memory location that is not anymore used at call_rcu(&f->f_rcuhead,
file_free_rcu) time, to reduce the size of this critical kernel object.

The trick I used is to move f_rcuhead and f_list in an union called f_u

The callers are changed so that f_rcuhead becomes f_u.fu_rcuhead and f_list
becomes f_u.f_list

Signed-off-by: Eric Dumazet <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/char/tty_io.c

···
 	check_tty_count(tty, "do_tty_hangup");
 	file_list_lock();
 	/* This breaks for file handles being sent over AF_UNIX sockets ? */
-	list_for_each_entry(filp, &tty->tty_files, f_list) {
+	list_for_each_entry(filp, &tty->tty_files, f_u.fu_list) {
 		if (filp->f_op->write == redirected_tty_write)
 			cons_filp = filp;
 		if (filp->f_op->write != tty_write)

fs/dquot.c

···
 restart:
 	file_list_lock();
 	list_for_each(p, &sb->s_files) {
-		struct file *filp = list_entry(p, struct file, f_list);
+		struct file *filp = list_entry(p, struct file, f_u.fu_list);
 		struct inode *inode = filp->f_dentry->d_inode;
 		if (filp->f_mode & FMODE_WRITE && dqinit_needed(inode, type)) {
 			struct dentry *dentry = dget(filp->f_dentry);

fs/file_table.c

···
 
 static inline void file_free_rcu(struct rcu_head *head)
 {
-	struct file *f =  container_of(head, struct file, f_rcuhead);
+	struct file *f =  container_of(head, struct file, f_u.fu_rcuhead);
 	kmem_cache_free(filp_cachep, f);
 }
 
 static inline void file_free(struct file *f)
 {
-	call_rcu(&f->f_rcuhead, file_free_rcu);
+	call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
 }
 
 /* Find an unused file structure and return a pointer to it.
···
 	f->f_gid = current->fsgid;
 	rwlock_init(&f->f_owner.lock);
 	/* f->f_version: 0 */
-	INIT_LIST_HEAD(&f->f_list);
+	INIT_LIST_HEAD(&f->f_u.fu_list);
 	return f;
 
 over:
···
 	if (!list)
 		return;
 	file_list_lock();
-	list_move(&file->f_list, list);
+	list_move(&file->f_u.fu_list, list);
 	file_list_unlock();
 }
 
 void file_kill(struct file *file)
 {
-	if (!list_empty(&file->f_list)) {
+	if (!list_empty(&file->f_u.fu_list)) {
 		file_list_lock();
-		list_del_init(&file->f_list);
+		list_del_init(&file->f_u.fu_list);
 		file_list_unlock();
 	}
 }
···
 	/* Check that no files are currently opened for writing. */
 	file_list_lock();
 	list_for_each(p, &sb->s_files) {
-		struct file *file = list_entry(p, struct file, f_list);
+		struct file *file = list_entry(p, struct file, f_u.fu_list);
 		struct inode *inode = file->f_dentry->d_inode;
 
 		/* File with pending delete? */

fs/proc/generic.c

···
 	 */
 	file_list_lock();
 	list_for_each(p, &sb->s_files) {
-		struct file * filp = list_entry(p, struct file, f_list);
+		struct file * filp = list_entry(p, struct file, f_u.fu_list);
 		struct dentry * dentry = filp->f_dentry;
 		struct inode * inode;
 		struct file_operations *fops;

fs/super.c

···
 	struct file *f;
 
 	file_list_lock();
-	list_for_each_entry(f, &sb->s_files, f_list) {
+	list_for_each_entry(f, &sb->s_files, f_u.fu_list) {
 		if (S_ISREG(f->f_dentry->d_inode->i_mode) && file_count(f))
 			f->f_mode &= ~FMODE_WRITE;
 	}

include/linux/fs.h

···
 #define RA_FLAG_INCACHE 0x02	/* file is already in cache */
 
 struct file {
-	struct list_head	f_list;
+	/*
+	 * fu_list becomes invalid after file_free is called and queued via
+	 * fu_rcuhead for RCU freeing
+	 */
+	union {
+		struct list_head	fu_list;
+		struct rcu_head 	fu_rcuhead;
+	} f_u;
 	struct dentry		*f_dentry;
 	struct vfsmount         *f_vfsmnt;
 	struct file_operations	*f_op;
···
 	spinlock_t		f_ep_lock;
 #endif /* #ifdef CONFIG_EPOLL */
 	struct address_space	*f_mapping;
-	struct rcu_head 	f_rcuhead;
 };
 extern spinlock_t files_lock;
 #define file_list_lock() spin_lock(&files_lock);

security/selinux/hooks.c

···
 
 	if (tty) {
 		file_list_lock();
-		file = list_entry(tty->tty_files.next, typeof(*file), f_list);
+		file = list_entry(tty->tty_files.next, typeof(*file), f_u.fu_list);
 		if (file) {
 			/* Revalidate access to controlling tty.
 			   Use inode_has_perm on the tty inode directly rather

security/selinux/selinuxfs.c

···
 
 	file_list_lock();
 	list_for_each(p, &sb->s_files) {
-		struct file * filp = list_entry(p, struct file, f_list);
+		struct file * filp = list_entry(p, struct file, f_u.fu_list);
 		struct dentry * dentry = filp->f_dentry;
 
 		if (dentry->d_parent != de) {