on since the last collection we
give partial credit for objects we expect to be explicitly deallocated.
Even if all objects are explicitly managed, it is often desirable to collect
on rare occasion, since that is our only mechanism for coalescing completely
empty chunks.
</ul>
<P>
It has been suggested that this should be adjusted so that we favor
expansion if the resulting heap still fits into physical memory.
In many cases, that would no doubt help.  But it is tricky to do this
in a way that remains robus