Global GC and address adjustment

Sometimes global GC takes a really long time (minutes) on my
Allegro/win32 system, and from the output generated with the :print
and :stats switches turned on, it appears that it is the "address
adjustment" phase that takes up most of that time.

What does "address adjustment" mean, and does anyone have any hint on
how to somehow reduce its impact?

Thanks,
-- 
Frode Vatvedt Fjeld