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>
Documentation: get rid of write_super

The '->write_super' superblock method is gone, and this patch removes all the
references to 'write_super' from various pieces of the kernel documentation.

Cc: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Documentation: fix the VM knobs descritpion WRT pdflush

The pdflush thread is long gone, however we still mention it incorrectly in the
kernel documentation. This patch fixes the situation.

Cc: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
ext3: nuke write_super from comments

The '->write_super' superblock method is gone, and this patch removes all the
references to 'write_super' from ext3.

Cc: Jan Kara <jack@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
ext4: nuke write_super from comments

The '->write_super' superblock method is gone, and this patch removes all the
references to 'write_super' from ext3.

Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
ext4: nuke pdflush from comments

The pdflush thread is long gone, so this patch removes references to pdflush
from ext4 comments.

Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
btrfs: nuke write_super from comments

The '->write_super' superblock method is gone, and this patch removes all the
references to 'write_super' from btrfs.

Cc: Chris Mason <chris.mason@fusionio.com>
Cc: linux-btrfs@vger.kernel.org
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
btrfs: nuke pdflush from comments

The pdflush thread is long gone, so this patch removes references to pdflush
from btrfs comments.

Cc: Chris Mason <chris.mason@fusionio.com>
Cc: linux-btrfs@vger.kernel.org
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
jbd/jbd2: nuke write_super from comments

The '->write_super' superblock method is gone, and this patch removes all the
references to 'write_super' from various jbd and jbd2.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jan Kara <jack@suse.cz>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
vfs: nuke pdflush from comments

The pdflush thread is long gone, so this patch removes references to pdflush
from vfs comments.

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

The '->write_super' superblock method is gone, and this patch removes all the
references to 'write_super' from hfs.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
nilfs2: nuke write_super from comments

The '->write_super' superblock method is gone, and this patch removes all the
references to 'write_super' from ntfs.

Cc: KONISHI Ryusuke <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
drbd: nuke pdflush from comments

The pdflush thread is long gone, so this patch removes references to pdflush
from drbd comments.

Cc: drbd-dev@lists.linbit.com
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
gfs2: nuke pdflush from comments

The pdflush thread is long gone, so this patch removes references to pdflush
from gfs comments.

Cc: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
UBIFS: nuke pdflush from comments

The pdflush thread is long gone, so this patch removes references to pdflush
from UBIFS comments.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
missed mnt_drop_write() in do_dentry_open()

This one ought to be __mnt_drop_write(), to match __mnt_want_write()
in the beginning...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Merge branch 'for-linus-2' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

Pull VFS fixes and cleanups from Al Viro.

Most of this is the series to remove sync_supers() and the
->write_supers VFS callback from Artem Bityutskiy.  One commit to do the
actual removal work, a whole series of commits to fix up stale comments
etc all over the tree.

There's also a regression fix for an incorrect use of mnt_drop_write()
in do_dentry_open().

* 'for-linus-2' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  missed mnt_drop_write() in do_dentry_open()
  UBIFS: nuke pdflush from comments
  gfs2: nuke pdflush from comments
  drbd: nuke pdflush from comments
  nilfs2: nuke write_super from comments
  hfs: nuke write_super from comments
  vfs: nuke pdflush from comments
  jbd/jbd2: nuke write_super from comments
  btrfs: nuke pdflush from comments
  btrfs: nuke write_super from comments
  ext4: nuke pdflush from comments
  ext4: nuke write_super from comments
  ext3: nuke write_super from comments
  Documentation: fix the VM knobs descritpion WRT pdflush
  Documentation: get rid of write_super
  vfs: kill write_super and sync_supers