[PATCH 0/2] Fix a couple of random hangs.

[Dave Chinner]

The first patch fixes a low memory hang where I/O completion
processing triggers memory reclaim which hangs waiting for
I/O completion. The trigger is unwritten extent conversion
blocking completion of normal writes.

The second fixes a log hang which results from excessive load;
we update the push target after we go to sleep so if we are
unlucky enough not to have a current push target far enough
advanced we'll hang.