This directory contains a quick and dirty log-structured
implementation of the MM.  This implementation overrides various pieces
of code implemented in the "mm" directory.

The basic idea is that the disk is divided into a number of large
fixed size regions (say about half a megabyte each).  The contents of
a segment are allowed to fragment over the disk because a segment is
not written back in place.  Instead, recent modifications are
collected up and written out a region at a time.  The various pieces
of disk storage that contain the current contents of a segment are
called "fragments".  Each region thus consists of a set of fragments.
The unit of writing to disk is a region, whereas the unit of reading
is a fragment.

TODO
====
* Invalidate cache entries when a region becomes empty.
