Roots under one 4 KiB unit, mostly runtime helpers, no longer count in the
partition loads that balancing compares. They are placed after the larger
roots, each in the first open partition from its name's partition whose
load from the larger roots is within the cap, so where a helper goes
depends only on the larger roots. A helper that an edit adds or removes
used to change the total and the cap and move several other roots, and
every partition they left or joined was compiled again.
A root's size also leaves out the digits of metadata references, which an
edit elsewhere in the module can renumber, so an unchanged function no
longer crosses a unit boundary because its references were renumbered.
Chris Tate
da6665a98a