vfs: kill write_super and sync_supers

Finally we can kill the 'sync_supers' kernel thread along with the
'->write_super()' superblock operation because all the users are gone.
Now every file-system is supposed to self-manage own superblock and
its dirty state.

The nice thing about killing this thread is that it improves power management.
Indeed, 'sync_supers' is a source of monotonic system wake-ups - it woke up
every 5 seconds no matter what - even if there were no dirty superblocks and
even if there were no file-systems using this service (e.g., btrfs and
journalled ext4 do not need it). So it was wasting power most of the time. And
because the thread was in the core of the kernel, all systems had to have it.
So I am quite happy to make it go away.

Interestingly, this thread is a left-over from the pdflush kernel thread which
was a self-forking kernel thread responsible for all the write-back in old
Linux kernels. It was turned into per-block device BDI threads, and
'sync_supers' was a left-over. Thus, R.I.P, pdflush as well.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 0 insertions, 4 deletions

diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index c97c6b9cd38e..2a9a9abc9126 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -124,7 +124,6 @@ void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
 void bdi_start_background_writeback(struct backing_dev_info *bdi);
 int bdi_writeback_thread(void *data);
 int bdi_has_dirty_io(struct backing_dev_info *bdi);
-void bdi_arm_supers_timer(void);
 void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi);
 void bdi_lock_two(struct bdi_writeback *wb1, struct bdi_writeback *wb2);
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 38dba16c4176..aa110476a95b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1491,7 +1491,6 @@ struct sb_writers {
 struct super_block {
         struct list_head        s_list;         /* Keep this first */
         dev_t                   s_dev;          /* search index; _not_ kdev_t */
-        unsigned char           s_dirt;
         unsigned char           s_blocksize_bits;
         unsigned long           s_blocksize;
         loff_t                  s_maxbytes;     /* Max file size */
@@ -1861,7 +1860,6 @@ struct super_operations {
         int (*drop_inode) (struct inode *);
         void (*evict_inode) (struct inode *);
         void (*put_super) (struct super_block *);
-        void (*write_super) (struct super_block *);
         int (*sync_fs)(struct super_block *sb, int wait);
         int (*freeze_fs) (struct super_block *);
         int (*unfreeze_fs) (struct super_block *);
@@ -2397,7 +2395,6 @@ extern int vfs_fsync_range(struct file *file, loff_t start, loff_t end,
                            int datasync);
 extern int vfs_fsync(struct file *file, int datasync);
 extern int generic_write_sync(struct file *file, loff_t pos, loff_t count);
-extern void sync_supers(void);
 extern void emergency_sync(void);
 extern void emergency_remount(void);
 #ifdef CONFIG_BLOCK