Re: [PATCH 1/2] mm/page_vma_mapped: use PMD_SIZE instead of calculating it

Kirill A. Shutemov
2019-12-02T08:03:19Z

On Thu, Nov 28, 2019 at 09:22:26PM +0000, Wei Yang wrote:
> On Thu, Nov 28, 2019 at 11:32:55AM +0300, Kirill A. Shutemov wrote:
> >On Thu, Nov 28, 2019 at 09:03:20AM +0800, Wei Yang wrote:
> >> At this point, we are sure page is PageTransHuge, which means
> >> hpage_nr_pages is HPAGE_PMD_NR.
> >>
> >> This is safe to use PMD_SIZE instead of calculating it.
> >>
> >> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
> >> ---
> >> mm/page_vma_mapped.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
> >> index eff4b4520c8d..76e03650a3ab 100644
> >> --- a/mm/page_vma_mapped.c
> >> +++ b/mm/page_vma_mapped.c
> >> @@ -223,7 +223,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
> >> if (pvmw->address >= pvmw->vma->vm_end ||
> >> pvmw->address >=
> >> __vma_address(pvmw->page, pvmw->vma) +
> >> - hpage_nr_pages(pvmw->page) * PAGE_SIZE)
> >> + PMD_SIZE)
> >> return not_found(pvmw);
> >> /* Did we cross page table boundary? */
> >> if (pvmw->address % PMD_SIZE == 0) {
> >
> >It is dubious cleanup. Maybe page_size(pvmw->page) instead? It will not
> >break if we ever get PUD THP pages.
> >
>
> Thanks for your comment.
>
> I took a look into the code again and found I may miss something.
>
> I found we support PUD THP pages, whilc hpage_nr_pages() just return
> HPAGE_PMD_NR on PageTransHuge. Why this is not possible to return PUD number?

We only support PUD THP for DAX. Means, we don't have struct page for it.

--
Kirill A. Shutemov