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

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Date:   Tue, 3 Dec 2019 12:47:30 +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 Mon, Dec 02, 2019 at 10:21:51PM +0000, Wei Yang wrote:
> On Mon, Dec 02, 2019 at 11:03:15AM +0300, Kirill A. Shutemov wrote:
> >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.
> >
> 
> BTW, may I ask why you suggest to use page_size() if we are sure only PMD THP
> page is used here? To be more generic?

Yeah. I would rather not touch it at all.

-- 
 Kirill A. Shutemov