Multiple page size support on FreeBSD?

[Benjamin Kaduk]

On Wed, 10 Apr 2013, Wojciech Puchar wrote:

>> How do your tests work?  Do you examine PTEs directly to check for 
>> superpages
>> or are you relying on the vm.pmap.pde sysctls?
>
> the later.
>
> anyway - algorithm described on list - that heuristics detects consecutive 
> page access doesn't really help the urgent case - RANDOM access to large 
> amount of memory.

The algorithm is not a heuristic based on consecutive accesses, promotion 
occurs when the entire superpage's worth of memory has actually been 
accessed.  If I remember correctly, the performance gain from superpages 
was only a few percent, so spending more time trying to decide when to use 
them would make the algorithm a net wash.

You should really watch the talk I linked to if you're interested, it was 
quite interesting.

> sequential access will get minimal improvement.
>
> IMHO the only way that really make sens is to add options to madvise to give 
> kernel information about usage.

Maybe.

-Ben Kaduk