[gclist] Time-stamping objects...

[Bill Bill]

|   Date: Mon, 15 Apr 1996 09:41:29 -0500
|   From: cef@geode.geodesic.com (Charles Fiterman)

|   Generational collectors eliminate fragmentation and if you have enough
|   storage are more efficient. In fact as the amount of storage increases
|   copying collectors approach zero overhead. If you never reach the end
|   of the space copying collectors have zero overhead. With this in mind
|   it makes sense to build execution frames on the heap.

You have to be very careful about this last claim because it is
generally not true.

The add/subtract instruction that deallocates a stack frame
simultaneously produces the pointer to the previous one.

If you allocate execution frames on the heap you will typically have
to load through a pointer to obtain the pointer to the previous one.
In addition, depending on your allocator you may need to write extra
header words (e.g. length of frame).

Thus even if you never trigger a collection, you will typically have
higher overhead for the heap-allocated execution frames than for the
stack-allocated frames.

A different issue is how expensive is call-with-current-continuation
and which way the trade-off should go there.