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    SubjectRe: [patch 3/6] mmu_notifier: invalidate_page callbacks
    On Thu, 14 Feb 2008 22:49:02 -0800 Christoph Lameter <clameter@sgi.com> wrote:

    > Two callbacks to remove individual pages as done in rmap code
    >
    > invalidate_page()
    >
    > Called from the inner loop of rmap walks to invalidate pages.
    >
    > age_page()
    >
    > Called for the determination of the page referenced status.
    >
    > If we do not care about page referenced status then an age_page callback
    > may be be omitted. PageLock and pte lock are held when either of the
    > functions is called.

    The age_page mystery shallows.

    It would be useful to have some rationale somewhere in the patchset for the
    existence of this callback.

    > #include <asm/tlbflush.h>
    >
    > @@ -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.

    > /* Pretend the page is referenced if the task has the
    > @@ -455,6 +457,7 @@ static int page_mkclean_one(struct page
    >
    > 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.



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