BTW I was looking at a sample update-only pull and seeing
why different commands needed to page in stuff from the
cset file.  Some interesting points:

- probekey pages in all of delta2 doing the tag graph probe
  because it contains ptag
- listkey pages in all of delta2 in sccs_tagcolor().  The
  graph walk goes to the root
- makepatch does an admin(ADMIN_BK) so that walks the entire
  delta table and pages in everything
- takepatch is fast until it needs to validate the checksum, then
  it reads the entire cset weave to compute the data structure.
  that pages in 40% of the heap.