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

Wei Yang
2019-11-28T21:22:31Z

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?

Search in the kernel tree, one implementation of PUD_SIZE fault is
dev_dax_huge_fault. If page fault happens here, would this if break the loop
too early?

>--
> Kirill A. Shutemov

--
Wei Yang
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