On Thu, Nov 23, 2023 at 06:22:33PM +0000, Christophe Leroy wrote:
> > For fast-gup I think the hugepd code is in use, however for walk_page_*
> > apis hugepd code shouldn't be reached iiuc as we have the hugetlb specific
> > handling (walk_hugetlb_range()), so anything within walk_pgd_range() to hit
> > a hugepd can be dead code to me (but note that this "dead code" is good
> > stuff to me, if one would like to merge hugetlb instead into generic mm).
> Not sure what you mean here. What do you mean by "dead code" ?
> A hugepage directory can be plugged at any page level, from PGD to PMD.
> So the following bit in walk_pgd_range() is valid and not dead:
>               if (is_hugepd(__hugepd(pgd_val(*pgd))))
>                       err = walk_hugepd_range((hugepd_t *)pgd, addr, next, 
> walk, PGDIR_SHIFT);

IMHO it boils down to the question on whether hugepd is only used in
hugetlbfs.  I think I already mentioned that above, but I can be more
explicit; what I see is that from higher stack in __walk_page_range():

        if (is_vm_hugetlb_page(vma)) {
                if (ops->hugetlb_entry)
                        err = walk_hugetlb_range(start, end, walk);
        } else
                err = walk_pgd_range(start, end, walk);

It means to me as long as the vma is hugetlb, it'll not trigger any code in
walk_pgd_range(), but only walk_hugetlb_range().  Do you perhaps mean
hugepd is used outside hugetlbfs?


Peter Xu

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