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From: Daniel Phillips <phillips@arcor.de>
To: Andrew Morton <akpm@zip.com.au>, Anton Blanchard <anton@samba.org>
Subject: Re: fix CONFIG_HIGHPTE
Date: Fri, 9 Aug 2002 16:07:24 +0200
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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
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