[PATCH 0/5] improved busy extent handling

[Christoph Hellwig]

This series optimizes how XFS deals with busy extents.  It starts to
track them exactly, and allows reuses where possible (metadata to metadata)
or else tries to avoid busy extents during allocations.  This means
we don't have a single log force due to busy extents during either
xfstests, compilebench or postmark on my testsystem, which can easily
be tracked using the new tracepoints added in the last patch.

This is a repost of the previous series and should address all review
comments.  The discard support, which relies on the exact busy extent
tracking has been dropped temporarily until I can fix up some issues
that I found during testing.