[PATCH 0/5] reiserfs: stop using write_supers and s_dirt

[Artem Bityutskiy <dedekind1@gmail.com>]

This patch-set makes reiserfs 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.

This patch-set makes reiserfs submit a delayed job for writing out old commits
instead of using 's_dirt'.

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.

The '->write_supers()' method is mostly used by baroque file-systems like hfs,
udf, etc. Modern file-systems like btrfs and xfs do not use it. This justifies
removing this stuff from VFS completely and make every FS self-manage own
superblock.

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 xfstests.

======
Overall status:

1. ext4: patches submitted, waiting for reply from Ted Ts'o:
   https://lkml.org/lkml/2012/4/2/111
   Ted keeps silence so far WRT the fate of this patch-set.
2. ext2:  done, see commit f72cf5e223a28d3b3ea7dc9e40464fd534e359e8
3. vfat:  done, see commit 78491189ddb6d84d4a4abae992ed891a236d0263
4. jffs2: sits the mtd subsystem tree, see commit
          208b14e507c00ff7f108e1a388dd3d8cc805a443 in
	  git://git.infradead.org/linux-mtd.git

TODO: affs, exofs, hfs, hfsplus, sysv, udf, ufs
======

Thanks,
Artem.