From: Eric Dumazet 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 Signed-off-by: Andrew Morton --- drivers/char/tty_io.c | 2 +- fs/dquot.c | 2 +- fs/file_table.c | 14 +++++++------- fs/proc/generic.c | 2 +- fs/super.c | 2 +- include/linux/fs.h | 9 +++++++-- security/selinux/hooks.c | 2 +- security/selinux/selinuxfs.c | 2 +- 8 files changed, 20 insertions(+), 15 deletions(-) diff -puN drivers/char/tty_io.c~reduce-sizeofstruct-file drivers/char/tty_io.c --- devel/drivers/char/tty_io.c~reduce-sizeofstruct-file 2005-09-24 18:45:09.000000000 -0700 +++ devel-akpm/drivers/char/tty_io.c 2005-09-24 18:45:09.000000000 -0700 @@ -809,7 +809,7 @@ static void do_tty_hangup(void *data) 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) diff -puN fs/dquot.c~reduce-sizeofstruct-file fs/dquot.c --- devel/fs/dquot.c~reduce-sizeofstruct-file 2005-09-24 18:45:09.000000000 -0700 +++ devel-akpm/fs/dquot.c 2005-09-24 18:45:09.000000000 -0700 @@ -662,7 +662,7 @@ static void add_dquot_ref(struct super_b 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); diff -puN fs/file_table.c~reduce-sizeofstruct-file fs/file_table.c --- devel/fs/file_table.c~reduce-sizeofstruct-file 2005-09-24 18:45:09.000000000 -0700 +++ devel-akpm/fs/file_table.c 2005-09-24 18:45:09.000000000 -0700 @@ -56,13 +56,13 @@ void filp_dtor(void * objp, struct kmem_ 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. @@ -95,7 +95,7 @@ struct file *get_empty_filp(void) 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: @@ -225,15 +225,15 @@ void file_move(struct file *file, struct 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(); } } @@ -245,7 +245,7 @@ int fs_may_remount_ro(struct super_block /* 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? */ diff -puN fs/proc/generic.c~reduce-sizeofstruct-file fs/proc/generic.c --- devel/fs/proc/generic.c~reduce-sizeofstruct-file 2005-09-24 18:45:09.000000000 -0700 +++ devel-akpm/fs/proc/generic.c 2005-09-24 18:45:09.000000000 -0700 @@ -533,7 +533,7 @@ static void proc_kill_inodes(struct proc */ 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; diff -puN fs/super.c~reduce-sizeofstruct-file fs/super.c --- devel/fs/super.c~reduce-sizeofstruct-file 2005-09-24 18:45:09.000000000 -0700 +++ devel-akpm/fs/super.c 2005-09-24 18:45:09.000000000 -0700 @@ -513,7 +513,7 @@ static void mark_files_ro(struct super_b 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; } diff -puN include/linux/fs.h~reduce-sizeofstruct-file include/linux/fs.h --- devel/include/linux/fs.h~reduce-sizeofstruct-file 2005-09-24 18:45:09.000000000 -0700 +++ devel-akpm/include/linux/fs.h 2005-09-24 18:45:09.000000000 -0700 @@ -573,7 +573,13 @@ struct file_ra_state { #define RA_FLAG_INCACHE 0x02 /* file is already in cache */ struct file { - struct list_head f_list; +/* + * f_list and f_rcuhead can share the same memory location + */ + 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; @@ -597,7 +603,6 @@ struct file { 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); diff -puN security/selinux/hooks.c~reduce-sizeofstruct-file security/selinux/hooks.c --- devel/security/selinux/hooks.c~reduce-sizeofstruct-file 2005-09-24 18:45:09.000000000 -0700 +++ devel-akpm/security/selinux/hooks.c 2005-09-24 18:45:09.000000000 -0700 @@ -1593,7 +1593,7 @@ static inline void flush_unauthorized_fi 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 diff -puN security/selinux/selinuxfs.c~reduce-sizeofstruct-file security/selinux/selinuxfs.c --- devel/security/selinux/selinuxfs.c~reduce-sizeofstruct-file 2005-09-24 18:45:09.000000000 -0700 +++ devel-akpm/security/selinux/selinuxfs.c 2005-09-24 18:45:09.000000000 -0700 @@ -914,7 +914,7 @@ static void sel_remove_bools(struct dent 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) { _