writeback fixes and cleanups for 2.6.40

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 wbc.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

The patches are also git pullable from

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

Thanks,
Fengguang