> 1) Minimal copying (all page moves would be virtual.)

On some systems (typically those using inverted page tables or
virtually-addressed caches; I'm thinking in particular of the IBM RT
and the HP PA...), random page-flipping like this can be more
expensive than copying, because you can't have a page mapped at
"random" virtual addresses at the same time in different processes, so
you have to flush one mapping, flush/purge any references in the cache
to that page, and take a sharing fault when you need the original
mapping again.

					- Bill