[gclist] Demand driven generational collector

[Pekka P. Pirinen]

> for two-generation systems, the widely known Appel collector does
> essentially that,

Also, Lisp Machine GC worked like that - I suppose Open Genera still
does.  There's a top generation, called the dynamic generation, and a
configurable number of "ephemeral" generations below that.  Each
ephemeral generation has a capacity, and is collected if it exceeds
its capacity.  I understand it worked well, although it required some
tweaking to configure it for demanding applications.

Collection scheduling in the MPS is based on the same principle,
complicated by mostly-copying collection, and a mechanism for the
client to restrict promotion when they're allocating a pig in the
python.
-- 
Pekka P. Pirinen, Global Graphics Software
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