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Subject: Re: vm changes from linux-2.6.14 to linux-2.6.15
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From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: Tue, 01 May 2007 10:00:19 +1000

> 
> > > Interesting - thanks for working that out.  Let's keep linux-mm on cc please.
> > 
> > You can't elide the update_mmu_cache() call on sun4c because that will
> > miss some critical TLB setups which are performed there.
> > 
> > The sun4c TLB has two tiers of entries:
> > 
> > 1) segment maps, these hold ptes for a range of addresses
> > 2) ptes, mapped into segment maps
> > 
> > update_mmu_cache() on sun4c take care of allocating and setting
> > up the segment maps, so if you elide the call this never happens
> > and we fault forever.
> 
> Maybe we can move that logic to ptep_set_access_flags()... in fact, the
> tlb flush logic should be done there too imho.
>
> There would still be the update_mmu_cache() that we don't want on
> powerpc in all cases I suppose. That can be done by having
> ptep_set_access_flags() return a boolean indicating wether
> update_mmu_cache() shall be called or not ...

Always doing ptep_set_access_flags() and returning a boolean like
that might be a good idea.