[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 <dada1@cosmosbay.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

8 files changed, 21 insertions, 15 deletions

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index f5649a337743..c586bfa852ee 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -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 --git a/fs/dquot.c b/fs/dquot.c
index 05f3327d64a3..ea7644227a65 100644
--- a/fs/dquot.c
+++ b/fs/dquot.c
@@ -662,7 +662,7 @@ static void add_dquot_ref(struct super_block *sb, int type)
 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 --git a/fs/file_table.c b/fs/file_table.c
index 86ec8ae985b4..4dc205546547 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -56,13 +56,13 @@ void filp_dtor(void * objp, struct kmem_cache_s *cachep, unsigned long dflags)
 
 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 list_head *list)
         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 *sb)
         /* 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 --git a/fs/proc/generic.c b/fs/proc/generic.c
index 8a8c34461d48..b638fb500743 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -533,7 +533,7 @@ static void proc_kill_inodes(struct proc_dir_entry *de)
          */
         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 --git a/fs/super.c b/fs/super.c
index 6e57ee252e14..f60155ec7780 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -513,7 +513,7 @@ static void mark_files_ro(struct super_block *sb)
         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 --git a/include/linux/fs.h b/include/linux/fs.h
index f83d997c5582..6d6226732c93 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -574,7 +574,14 @@ struct file_ra_state {
 #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;
@@ -598,7 +605,6 @@ 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 --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index d50d7a782cf5..bb62838be496 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1609,7 +1609,7 @@ static inline void flush_unauthorized_files(struct files_struct * files)
 
         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 --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
index 7a387fec2a0c..fdc382389720 100644
--- a/security/selinux/selinuxfs.c
+++ b/security/selinux/selinuxfs.c
@@ -914,7 +914,7 @@ static void sel_remove_bools(struct dentry *de)
 
         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) {