Commit 4ba1119c authored by Matthew Wilcox (Oracle)'s avatar Matthew Wilcox (Oracle)
Browse files

mm: Add folio_mapcount() 



This implements the same algorithm as total_mapcount(), which is
transformed into a wrapper function.

Signed-off-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
parent 74e8ee47

include/linux/mm.h

+7 −1
Original line number Diff line number Diff line
@@ -825,8 +825,14 @@ static inline int page_mapcount(struct page *page) 
	return atomic_read(&page->_mapcount) + 1;

}



int folio_mapcount(struct folio *folio);



#ifdef CONFIG_TRANSPARENT_HUGEPAGE

int total_mapcount(struct page *page);

static inline int total_mapcount(struct page *page)

{

	return folio_mapcount(page_folio(page));

}



int page_trans_huge_mapcount(struct page *page);

#else

static inline int total_mapcount(struct page *page)

mm/huge_memory.c

+0 −24
Original line number Diff line number Diff line
@@ -2465,30 +2465,6 @@ static void __split_huge_page(struct page *page, struct list_head *list, 
	}

}



int total_mapcount(struct page *page)

{

	int i, compound, nr, ret;



	VM_BUG_ON_PAGE(PageTail(page), page);



	if (likely(!PageCompound(page)))

		return atomic_read(&page->_mapcount) + 1;



	compound = compound_mapcount(page);

	nr = compound_nr(page);

	if (PageHuge(page))

		return compound;

	ret = compound;

	for (i = 0; i < nr; i++)

		ret += atomic_read(&page[i]._mapcount) + 1;

	/* File pages has compound_mapcount included in _mapcount */

	if (!PageAnon(page))

		return ret - compound * nr;

	if (PageDoubleMap(page))

		ret -= nr;

	return ret;

}



/*

 * This calculates accurately how many mappings a transparent hugepage

 * has (unlike page_mapcount() which isn't fully accurate). This full

mm/util.c

+33 −0
Original line number Diff line number Diff line
@@ -740,6 +740,39 @@ int __page_mapcount(struct page *page) 
}

EXPORT_SYMBOL_GPL(__page_mapcount);



/**

 * folio_mapcount() - Calculate the number of mappings of this folio.

 * @folio: The folio.

 *

 * A large folio tracks both how many times the entire folio is mapped,

 * and how many times each individual page in the folio is mapped.

 * This function calculates the total number of times the folio is

 * mapped.

 *

 * Return: The number of times this folio is mapped.

 */

int folio_mapcount(struct folio *folio)

{

	int i, compound, nr, ret;



	if (likely(!folio_test_large(folio)))

		return atomic_read(&folio->_mapcount) + 1;



	compound = folio_entire_mapcount(folio);

	nr = folio_nr_pages(folio);

	if (folio_test_hugetlb(folio))

		return compound;

	ret = compound;

	for (i = 0; i < nr; i++)

		ret += atomic_read(&folio_page(folio, i)->_mapcount) + 1;

	/* File pages has compound_mapcount included in _mapcount */

	if (!folio_test_anon(folio))

		return ret - compound * nr;

	if (folio_test_double_map(folio))

		ret -= nr;

	return ret;

}



/**

 * folio_copy - Copy the contents of one folio to another.

 * @dst: Folio to copy to.