Re: [patch 1/4] mmu_notifier: Core code

Robin Holt
2008-01-26T11:58:27Z

> > > 1. invalidate_all()
> >
> > That will be fine as long as we can unregister the ops notifier and free
> > the structure. Otherwise, we end up being called needlessly.
>
> No you cannot do that because there are still callbacks that come later.
> The invalidate_all may lead to invalidate_range() doing nothing for this
> mm. The ops notifier and the freeing of the structure has to wait until
> release().

Could you be a little more clear here? If you are saying that the other
callbacks will need to do work? I can assure you we will clean up those
pages and raise memory protections. It will also be done in a much more
efficient fashion than the individual callouts.

If, on the other hand, you are saying we can not because of the way
we traverse the list, can we return a result indicating to the caller
we would like to be unregistered and then the mmu_notifier code do the
remove followed by a call to the release notifier?

>
> > > 2. invalidate_range() for each vma
> > >
> > > 3. release()
> > >
> > > We cannot simply move the call up because there will be future range
> > > callbacks on vma invalidation.
> >
> > I am not sure what this means. Right now, if you were to notify XPMEM
> > the process is exiting, we would take care of all the recalling of pages
> > exported by this process, clearing those pages cache lines from cache,
> > and raising memory protections. I would assume that moving the callout
> > earlier would expect the same of every driver.
>
> That does not sync with the current scheme of the invalidate_range()
> hooks. We would have to do a global invalidate early and then place the
> other invalidate_range hooks in such a way that none is called in later in
> process exit handling.

But if the notifier is removed from the list following the invalidate_all
callout, there would be no additional callouts.

Thanks,
Robin