linux-kernel - Re: [PATCH 1/2] mm/page_vma_mapped: use PMD

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Date:   Mon, 2 Dec 2019 11:03:15 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Wei Yang <richard.weiyang@...il.com>
Cc:     Wei Yang <richardw.yang@...ux.intel.com>,
        akpm@...ux-foundation.org, kirill.shutemov@...ux.intel.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm/page_vma_mapped: use PMD_SIZE instead of
 calculating it

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@...ux.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