Some GC measurements

["Adam D. Moss" <adam@...>]

From my app 5.1w4 with generational forced to 0:

GCSTEPMUL->  2       8       16

 GCPACE      82.3    80.0    78.0    worst-case FPS
   2         4900    3900    3800    peak mem usage

   4         86.5    84.7    85.1
             5600    4900    4700

   8         88.3    88.2    87.1
             7800    6900    6900

Peakmem results do seem more stable (and a bit better)
than with generational allowed, though it's not really
a panacea.

With generational disabled, the 5.1w4 default for
GCSTEPMUL (8) looks reasonable, though a default GCPACE
of 8 still looks a bit high for a good peakmem (but is
thankfully runtime-tuneable).

--Adam