[PATCHv4 0/5] ext4: stop using write_super and s_dirt

From: Artem Bityutskiy
Date: Wed Jul 04 2012 - 08:21:27 EST

This patch-set makes ext4 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.

Most of the ext4 changes were done or suggested by Jan Kara (thanks!). This
patch does not do anything complex - we basically notice that ext4 does not
really needd the 'write_super()' functionality and we can remove it. We
mark the superblock buffer as dirty directly, rather than posponing this till
the next 'sync_supers()' kernel thread wake-up.

Tested with xfstests (both journalled and non-journalled ext4 modes).


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.

Overall status:

1. ext4: patches submitted,
2. exofs: patch submitted,
3. sysv: patches submitted,
4. udf: patch submitted, sits in Jan Kara's tree:
git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs for_testing
5. affs: patches submitted, sit in Al Viro's tree:
git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs for-next
6. hfs: patches submitted, sit Andrew Morton's tree
7. hfsplus: patches submitted, sit in Andrew Morton's tree:
8. ext2: done, see commit f72cf5e223a28d3b3ea7dc9e40464fd534e359e8
9. vfat: done, see commit 78491189ddb6d84d4a4abae992ed891a236d0263
10. jffs2: done, see commit 208b14e507c00ff7f108e1a388dd3d8cc805a443
11. reiserfs: done, see commit 033369d1af1264abc23bea2e174aa47cdd212f6f

TODO: ufs

fs/ext4/ext4.h | 10 +---------
fs/ext4/ext4_jbd2.c | 9 ++-------
fs/ext4/ext4_jbd2.h | 7 ++-----
fs/ext4/file.c | 14 +++++++++++++-
fs/ext4/ialloc.c | 2 --
fs/ext4/inode.c | 2 +-
fs/ext4/mballoc.c | 2 --
fs/ext4/namei.c | 4 ++--
fs/ext4/resize.c | 2 +-
fs/ext4/super.c | 15 ++-------------
10 files changed, 24 insertions(+), 43 deletions(-)

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