Hybrid GC/explicit MMGs?

Hi,

the unpredictability of GC runs, be it real or percieved, got me
thinking about the possibility of hybrid system that allows
explicit freeing of ojbects (possibly prematurely so, with the
obvious consequences) and provides garbage collection.  Wouldn't
it be nice to say, "Now is a good time to clean up manually" ...

Besides the more obvious questions (given address 0xbfbff054, should
GC free it, or will the program free it?  Should GC take precedence?
Should explicit free'ing be in command?), I'm wondering whether two
such systems can even co-exist behind the same process (who gets to
do the next brk?  Is that my page or your page?)

Does anyone know about any system that has addressed (sic) this problem
or provides a similar approach?  Any thoughts why this may be possible,
impossible or possible-but-only-with-significant-overhead?

Note, if replies come in via PM, I'll post a summary.

Cheers,
Florian
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