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SubjectRe: [PATCHv5 20/28] mm: differentiate page_mapped() from page_mapcount() for compound pages
On 04/23/2015 11:03 PM, Kirill A. Shutemov wrote:
> Let's define page_mapped() to be true for compound pages if any
> sub-pages of the compound page is mapped (with PMD or PTE).
>
> On other hand page_mapcount() return mapcount for this particular small
> page.
>
> This will make cases like page_get_anon_vma() behave correctly once we
> allow huge pages to be mapped with PTE.
>
> Most users outside core-mm should use page_mapcount() instead of
> page_mapped().

Does "should" mean that they do that now, or just that you would like
them to? Should there be a warning before the function then?

>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Tested-by: Sasha Levin <sasha.levin@oracle.com>

> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -909,7 +909,16 @@ static inline pgoff_t page_file_index(struct page *page)

(not shown in the diff)

* Return true if this page is mapped into pagetables.
> */

Expand the comment? Especially if you put compound_head() there.

> static inline int page_mapped(struct page *page)

Convert to proper bool while at it?

> {
> - return atomic_read(&(page)->_mapcount) + compound_mapcount(page) >= 0;
> + int i;
> + if (likely(!PageCompound(page)))
> + return atomic_read(&page->_mapcount) >= 0;
> + if (compound_mapcount(page))
> + return 1;
> + for (i = 0; i < hpage_nr_pages(page); i++) {
> + if (atomic_read(&page[i]._mapcount) >= 0)
> + return 1;
> + }
> + return 0;
> }
>
> /*



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