[Xen-devel] Re: [PATCH 1 of 4] mm: add a ptep_modify_prot transaction abstraction

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

Benjamin Herrenschmidt wrote:
> On Wed, 2008-06-18 at 17:24 -0700, Linus Torvalds wrote:
>   
> > On Wed, 18 Jun 2008, Jeremy Fitzhardinge wrote:
> >     
> > > Along the lines of:
> > >       
> > Hell no. There's a reason we have a special set_wrprotect() thing. We can 
> > do it more efficiently on native hardware by just clearing the bit 
> > atomically. No need to do the cmpxchg games.
> >     
> But we can't batch ... 
>   
Which architecture are you interested in?  If it isn't x86, you can 
probably get anything past Linus ;)
I'll do some measurements to see what effect the batchable 
ptep_set_wrprotect() has on native.  If it's significant, I'll propose 
making it conditional on CONFIG_PARAVIRT.
   J

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