I did some more experiments and that's the most I can get from the script, no matter how much free memory there is on the machine.
Adding ./pharo --memory 2000m ... has no effect.


[PhilMac:~/Documents/Smalltalk/2-MyWorkspaces/workspaceMemTest philippeback$] ./pharo Pharo.image memtest.st 501 1024000
memtest.st
uptime 0h0m0s
memory 25,004,444 bytes
old 19,213,688 bytes (76.80000000000001%)
young 5,384 bytes (0.0%)
used 19,219,072 bytes (76.9%)
free 5,785,372 bytes (23.1%)
GCs 5 (62ms between GCs)
full 1 totalling 76ms (24.5% uptime), avg 76.0ms
incr 4 totalling 10ms (3.2% uptime), avg 2.5ms
tenures 0

allocating: 501 times 1024000 bytes
allocated: 513.02 MB
time to run 0:00:00:06.27
3 times GC
time to run 0:00:00:00.494
uptime 0h0m7s
memory 534,974,360 bytes
old 532,256,456 bytes (99.5%)
young 7,092 bytes (0.0%)
used 532,263,548 bytes (99.5%)
free 2,710,812 bytes (0.5%)
GCs 344 (21ms between GCs)
full 87 totalling 5,822ms (82.2% uptime), avg 66.9ms
incr 257 totalling 659ms (9.3% uptime), avg 2.6ms
tenures 0
Since last view 339 (20ms between GCs)
uptime 6.800000000000001s
full 86 totalling 5,746ms (84.9% uptime), avg 66.8ms
incr 253 totalling 649ms (9.600000000000001% uptime), avg 2.6ms
tenures 0