Comment 47 for bug 635834

(In reply to comment #44)
> Ah, fault ahead is why MAP_POPULATE is important.
>
> Note that RPM achieved a 10% increase in upgrade performance
> (measured by wallclock ;-) by changing mmap(2) flags in 3
> places as well as using a larger (16Mb but 256 Kb had most of the gain)
> buffer for zlib way back when.
>
> Linux kernels have an astonishing amount of read ahead
> bandwidth available and often unused.

Great, you have noticed yourself before I've finished my comment ;)
The flag is relatively new - and not available on older systems.