Re: fix CONFIG_HIGHPTE

Daniel Phillips
2002-08-09T14:02:53Z

On Wednesday 07 August 2002 04:57, Andrew Morton wrote:
> Anton Blanchard wrote:
> > On ppc64 shared pagetables will require significant changes to the way
> > we handle the hardware hashtable. So add that to the "more and more crap
> > in there to support these pte_chains"
>
> Last I heard, pagetable sharing wasn't working out too well
> because they all get unshared.

That's only when you fork from a process with a minimal amount of VM mapped,
such as bash, which has 3 page tables allocated to it, all of which get
unshared. The situation is entirely different if you fork from a process
that has malloced more than a few meg, or beaten on a large mmap. Page table
sharing turns in a significant win there.

> > Will shared pagetables be a requirement or can we turn it on per arch?
>
> It's doubtful if per-arch would be an option.

It's currently expressed as a config option. As it's purely an optimization
there's no reason to do otherwise. Disabling it per-arch should be trivial.

> - We'll continue to suck for the University workload.

That seems likely ;-)

--
Daniel