[PATCH v7 15/28] mm: Add folio_mapcount

[Matthew Wilcox (Oracle)]

This is the folio equivalent of page_mapcount().

Signed-off-by: Matthew Wilcox (Oracle) <willy at infradead.org>
Reviewed-by: Christoph Hellwig <hch at lst.de>
Acked-by: Jeff Layton <jlayton at kernel.org>
---
 include/linux/mm.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 143b354c3f4a..7bd2ce197e2f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -883,6 +883,22 @@ static inline int page_mapcount(struct page *page)
 	return atomic_read(&page->_mapcount) + 1;
 }
 
+/**
+ * folio_mapcount - The number of mappings of this folio.
+ * @folio: The folio.
+ *
+ * The result includes the number of times any of the pages in the
+ * folio are mapped to userspace.
+ *
+ * Return: The number of page table entries which refer to this folio.
+ */
+static inline int folio_mapcount(struct folio *folio)
+{
+	if (unlikely(FolioMulti(folio)))
+		return __page_mapcount(&folio->page);
+	return atomic_read(&folio->_mapcount) + 1;
+}
+
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 int total_mapcount(struct page *page);
 int page_trans_huge_mapcount(struct page *page, int *total_mapcount);
-- 
2.30.2