Re: [PATCH 3/8] mmu_notifier: add event information to address invalidation v3

[Jerome Glisse <j.glisse@gmail.com>]

On Wed, Jul 09, 2014 at 06:32:08PM +0200, Joerg Roedel wrote:
> On Tue, Jul 08, 2014 at 06:00:00PM -0400, j.glisse@gmail.com wrote:
> > From: Jerome Glisse <jglisse@redhat.com>
> > 
> > The event information will be usefull for new user of mmu_notifier API.
> > The event argument differentiate between a vma disappearing, a page
> > being write protected or simply a page being unmaped. This allow new
> > user to take different path for different event for instance on unmap
> > the resource used to track a vma are still valid and should stay around.
> > While if the event is saying that a vma is being destroy it means that any
> > resources used to track this vma can be free.
> > 
> > Changed since v1:
> >   - renamed action into event (updated commit message too).
> >   - simplified the event names and clarified their intented usage
> >     also documenting what exceptation the listener can have in
> >     respect to each event.
> > 
> > Changed since v2:
> >   - Avoid crazy name.
> >   - Do not move code that do not need to move.
> 
> Okay, I can actually see use-cases for something like this. Given the
> number of invalidate_range_start/end call-sites and the semantics of
> these call-backs it would allow certain optimizations to know details of
> whats going on between these calls.
> 
> But why do you need this event information for all the other
> mmu_notifier call-backs? In change_pte for example you already get the
> address and the new pte value, isn't that enough to find out whats going
> on?
> 

For hmm no, because hmm do not know the old pte value. Thus have no idea.
But right as i am not going to further use change_pte i do not mind much
about it so i can drop it for change_pte. But other user might still find
that useful as it avoids them to lookup the old pte and do a comparison.

Cheers,
Jerome

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