simplify dirty buffer tracking

[Christoph Hellwig <hch@lst.de>]

Hi all,

this series rewrites the tracking and writeback of the per-transaction
or per-tree_log dirty buffers.  It is intended as a first step towards
getting rid of btree_inode, but turns out to be a pretty nice cleanup
on it's own.  I also see minor speedup in fs_mark workloads, but given
how variable they are in general I'm not sure if they really matter.

This series starts out new extent_buffer.[ch].  I plan to eventually
concentrate all code for extent_buffer handling there, but for now
this just has brand-new code.

Note that the series is based on top of net-next because the previous
round of extent_buffer changes has not made it to misc-next yet.

Diffstat:
 fs/btrfs/Makefile                |    2 
 fs/btrfs/ctree.h                 |    3 
 fs/btrfs/disk-io.c               |   72 +++++--------
 fs/btrfs/extent-io-tree.c        |  212 ---------------------------------------
 fs/btrfs/extent-io-tree.h        |   14 --
 fs/btrfs/extent-tree.c           |   21 ---
 fs/btrfs/extent_buffer.c         |  104 +++++++++++++++++++
 fs/btrfs/extent_buffer.h         |   26 ++++
 fs/btrfs/extent_io.c             |  131 ++++++------------------
 fs/btrfs/extent_io.h             |    2 
 fs/btrfs/fs.h                    |    3 
 fs/btrfs/tests/extent-io-tests.c |    2 
 fs/btrfs/transaction.c           |  168 ++----------------------------
 fs/btrfs/transaction.h           |    3 
 fs/btrfs/tree-log.c              |   71 ++++++++-----
 fs/btrfs/zoned.c                 |   11 +-
 include/trace/events/btrfs.h     |   57 ----------
 17 files changed, 278 insertions(+), 624 deletions(-)