writeback fixes and cleanups for 2.6.40 (v2)

Andrew,

This is the combination of all the recent writeback patches that get reasonably reviewed and tested.

The first 10 patches are already in -mm tree, with updates:

- remove "writeback: pass writeback_control down to move_expired_inodes()", and resolve the resulting merge conflicts in other patches.
- move ahead the sync livelock prevention patches (01, 02) so that (04) won't livelock sync
- merge the three -mm fixes to (08)
- fixed changelog of (01)

[PATCH 01/17] writeback: introduce .tagged_sync for the WB_SYNC_NONE sync stage [PATCH 02/17] writeback: update dirtied_when for synced inode to prevent livelock [PATCH 03/17] writeback: introduce writeback_control.inodes_cleaned [PATCH 04/17] writeback: try more writeback as long as something was written [PATCH 05/17] writeback: the kupdate expire timestamp should be a moving target [PATCH 06/17] writeback: sync expired inodes first in background writeback [PATCH 07/17] writeback: refill b_io iff empty
[PATCH 08/17] writeback: split inode_wb_list_lock into bdi_writeback.list_lock [PATCH 09/17] writeback: elevate queue_io() into wb_writeback() [PATCH 10/17] writeback: avoid extra sync work at enqueue time

The following 7 patches were posted and reviewed these days:

[PATCH 11/17] writeback: add bdi_dirty_limit() kernel-doc [PATCH 12/17] writeback: skip balance_dirty_pages() for in-memory fs [PATCH 13/17] writeback: remove writeback_control.more_io [PATCH 14/17] writeback: make writeback_control.nr_to_write straight [PATCH 15/17] writeback: remove .nonblocking and .encountered_congestion [PATCH 16/17] writeback: trace event writeback_single_inode [PATCH 17/17] writeback: trace event writeback_queue_io

Thanks to Jan and Dave for the careful reviews!

The patches are git pullable from

git://git.kernel.org/pub/scm/linux/kernel/git/wfg/writeback.git fs-writeback

Thanks,
Fengguang