[ofa-general] Re: [patch 3/6] mmu_notifier: invalidate_page callbacks

Christoph Lameter
2008-02-16T19:22:18Z

On Fri, 15 Feb 2008, Andrew Morton wrote:

> > @@ -287,7 +288,8 @@ static int page_referenced_one(struct pa
> > if (vma->vm_flags & VM_LOCKED) {
> > referenced++;
> > *mapcount = 1; /* break early from loop */
> > - } else if (ptep_clear_flush_young(vma, address, pte))
> > + } else if (ptep_clear_flush_young(vma, address, pte) |
> > + mmu_notifier_age_page(mm, address))
> > referenced++;
>
> The "|" is obviously deliberate. But no explanation is provided telling us
> why we still call the callback if ptep_clear_flush_young() said the page
> was recently referenced. People who read your code will want to understand
> this.

Andrea?

> > flush_cache_page(vma, address, pte_pfn(*pte));
> > entry = ptep_clear_flush(vma, address, pte);
> > + mmu_notifier(invalidate_page, mm, address);
>
> I just don't see how ths can be done if the callee has another thread in
> the middle of establishing IO against this region of memory.
> ->invalidate_page() _has_ to be able to block. Confused.

The page lock is held and that holds off I/O?