[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>

4 files changed, 10 insertions, 10 deletions

diff --git a/fs/dquot.c b/fs/dquot.c
index 05f3327..ea76442 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 86ec8ae..4dc2055 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 8a8c344..b638fb5 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 6e57ee2..f60155e 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;
 	}