[PATCH 0/6] hfs: stop using write_supers and s_dirt

[Artem Bityutskiy <dedekind1@gmail.com>]

This patch-set makes HFS file-system stop using the VFS '->write_supers()'
call-back and the '->s_dirt' superblock field because I plan to remove them
once all users are gone.

Like the other similar patch-sets, we switch to a delayed job for writing out
the superblock instead of using the 's_dirt' flag. Additionally, this patch-set
includes several clean-ups.

Reminder:

The goal is to get rid of the 'sync_supers()' kernel thread. This kernel thread
wakes up every 5 seconds (by default) and calls '->write_super()' for all
mounted file-systems. And the bad thing is that this is done even if all the
superblocks are clean. Moreover, many file-systems do not even need this end
they do not register the '->write_super()' method at all (e.g., btrfs).

So 'sync_supers()' most often just generates useless wake-ups and wastes power.
I am trying to make all file-systems independent of '->write_super()' and plan
to remove 'sync_supers()' and '->write_super()' completely once there are no
more users.

Al, in the past I was trying to upstream patches which optimized 'sync_super()',
but you wanted me to kill it completely instead, which I am trying to do
now, see http://lkml.org/lkml/2010/7/22/96

Tested using the fsstress test from the LTP project.

======
Overall status:

1. ext4: patches submitted, waiting for review from Ted Ts'o:
   https://lkml.org/lkml/2012/4/2/111
2. udf: patch submitted, should be in Jan Kara's tree:
   https://lkml.org/lkml/2012/6/4/233
3  exofs: patch submitted, not sure if it will go to the exofs tree:
   https://lkml.org/lkml/2012/6/4/211
4. affs: patches submitted, should be in Al Viro's tree:
   https://lkml.org/lkml/2012/6/6/400
4. ext2:     done, see commit f72cf5e223a28d3b3ea7dc9e40464fd534e359e8
5. vfat:     done, see commit 78491189ddb6d84d4a4abae992ed891a236d0263
6. jffs2:    done, see commit 208b14e507c00ff7f108e1a388dd3d8cc805a443
7. reiserfs: done, see commit 033369d1af1264abc23bea2e174aa47cdd212f6f

TODO: hfsplus, sysv, ufs
======

 fs/hfs/extent.c |    2 +-
 fs/hfs/hfs_fs.h |   15 +++++++----
 fs/hfs/inode.c  |   14 +++-------
 fs/hfs/mdb.c    |   15 +++++++++++
 fs/hfs/super.c  |   73 +++++++++++++++++++++++++++----------------------------
 5 files changed, 65 insertions(+), 54 deletions(-)

Thanks,
Artem.