IO-less dirty throttling v9

Hi,

The core bits of the IO-less balance_dirty_pages().

git://git.kernel.org/pub/scm/linux/kernel/git/wfg/writeback.git dirty-throttling-v9

Changes since v8:

- a lot of renames and comment/changelog rework
- use 3rd order polynomial as the global control line (Peter)
- stabilize dirty_ratelimit by decreasing update step size on small errors
- limit per-CPU dirtied pages to avoid dirty pages run away on 1k+ tasks (Peter)

Thanks a lot to Peter and Andrea, Vivek for the careful reviews!

shortlog:

Wu Fengguang (5):
writeback: account per-bdi accumulated dirtied pages
writeback: dirty position control
writeback: dirty rate control
writeback: per task dirty rate limit
writeback: IO-less balance_dirty_pages()

The last 4 patches are one single logical change, but splitted here to make it easier to review the different parts of the algorithm.

diffstat:

	 fs/fs-writeback.c                |    2 
	 include/linux/backing-dev.h      |    8 
	 include/linux/sched.h            |    7 
	 include/linux/writeback.h        |    1 
	 include/trace/events/writeback.h |   24 -
	 kernel/fork.c                    |    3 
	 mm/backing-dev.c                 |    3 
	 mm/page-writeback.c              |  544 ++++++++++++++++++++---------
	 8 files changed, 414 insertions(+), 178 deletions(-)

Thanks,
Fengguang