Re: Hugh's alternate page fault scalability approach on 512p Altix

[Christoph Lameter <clameter@engr.sgi.com>]

On Wed, 7 Sep 2005, Martin J. Bligh wrote:

> > Anticipatory prefaulting raises the highest fault rate obtainable three-fold
> > through gang scheduling faults but may allocate some pages to a task that are
> > not needed.
> 
> IIRC that costed more than it saved, at least for forky workloads like a
> kernel compile - extra cost in zap_pte_range etc. If things have changed
> substantially in that path, I guess we could run the numbers again - has
> been a couple of years.

Right. The costs come about through wrong anticipations installing useless 
mappings. The patches that I posted have this feature off by default. Gang 
scheduling can be enabled by modifying a value in /proc. But I guess the 
approach is essentially dead unless others want this feature too. The 
current page fault scalability approach should be fine for a couple of 
years and who knows what direction mmu technology has taken then.