Re: [PATCH] mm/page_vma_mapped.c: Exactly compare hugetlbfs page's pfn in pfn_in_hpage()

["Kirill A. Shutemov" <kirill@shutemov.name>]

On Thu, Jan 09, 2020 at 06:44:40AM +0000, Li Xinhai wrote:
> check_pte is called for hugetlbfs page and comparing pfn in pfn_in_page,
> where pfn is compared in range [hpage_pfn, hpage_pfn+HPAGE_PMD_NR). Now
> change it to match exactly for hugetlbfs page to avoid hiding any
> potential problems.

Hm. What potential problems do you talk about?

I understand that for hugetlb pages pfn is always has to be equal
hpage_pfn, but returning false for pfn in the range of the hugetlb page
just because it's not head is not helpful.

I would rather have

	VM_BUG_ON_PAGE(PageHuge(hpage) && pfn != hpage_pfn, hpage);

there.
> 
> Signed-off-by: Li Xinhai <lixinhai.lxh@gmail.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
>  mm/page_vma_mapped.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
> index eff4b45..434978b 100644
> --- a/mm/page_vma_mapped.c
> +++ b/mm/page_vma_mapped.c
> @@ -55,6 +55,8 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw)
>  static inline bool pfn_in_hpage(struct page *hpage, unsigned long pfn)
>  {
>  	unsigned long hpage_pfn = page_to_pfn(hpage);
> +	if (unlikely(PageHuge(hpage)))
> +		return pfn == hpage_pfn;
>  
>  	/* THP can be referenced by any subpage */
>  	return pfn >= hpage_pfn && pfn - hpage_pfn < hpage_nr_pages(hpage);
> -- 
> 1.8.3.1
> 
> 

-- 
 Kirill A. Shutemov