Sorry - a little off track - I don't see where the OP has tried running ltrace with syscalls enabled - or strace.

The differences probably are due to OS implementation - maybe a lot of calls to brk in one OS and not the other. It's worth the 2 minutes it takes to execute Otheus' code under strace on each box. That would rule out an odd kernel setting or some implementation "feature" as the root cause of the differences. If you see odd behavior, like a lot of system calls on one box and not on the the other, maybe someone can relate that to something useful.