Garbage collection

David Brown <>
Fri Sep 3 16:44:44 CEST 1999


>>>>> On Thu,  2 Sep 1999 23:38:42 -0700 (PDT), Patrick Logan <> said:

> A problem with a heap per process seems to be how much heap to
> allocate to each process, and handling the processes that outgrow
> their heap.

Another approach would be to do something like Caml Light.  Each
process has a small heap.  Objects that are smaller than a certain
size are allocated from this heap.  When a process does a minor
collection, its live data is moved to the shared heap.  This
per-process heap is usually something small, like 32k.  (The small
heap is also only for non-mutable objects).

The large heap is the collected in a more coordinated way.  This ends
up as a kind of hybrid copying and mark-sweep collector.  The first
generation is copying (but only for small objects), and the subsequent
generation is collected normally.

The large heap will need to use a real time collection algorithm,
whereas the small heaps can just be copied through in their entirery.
They can be chosen to be small enough that this collection runs fast
enough.

When a message is passed, it is checked to see which heap it is in,
and only if it is in a small heap is it copied.  That way, especially
large messages will avoid the copy.

I'm still looking for the article.  Hopefully I will find it when I
return from my trip (Monday is a holiday in the US).

Dave Brown




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