Is that difference twixt allocation protocols a 2.4.x kernel vs. 2.6.n kerrnel difference (i.e. generic to ANY AMD64 linux) or something else ?
9.1 and 9.3 both use 2.6 kernels. It was a change at some point in 2.6 that helps I/O clustering, because it is more likely that multiple pages lie next to each other in memory and can be submitted to the disk with a single request. 2.4 didn't have it. It's not AMD64 specific. As an additional side effect it makes Linux more hardware bug-to-bug compatible with some other popular OS. Previously machines with broken memory near the end tended to work mostly with that one as long as memory was not filled up, but fail early with Linux. Now they should mostly work with Linux too. Of course when memory eventually fills up you still have a problem. -Andi