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-rw-r--r--include/linux/mm.h15
1 files changed, 13 insertions, 2 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5a323422d783..f3fe7371855c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -782,6 +782,11 @@ static inline void *kvcalloc(size_t n, size_t size, gfp_t flags)
extern void kvfree(const void *addr);
+/*
+ * Mapcount of compound page as a whole, does not include mapped sub-pages.
+ *
+ * Must be called only for compound pages or any their tail sub-pages.
+ */
static inline int compound_mapcount(struct page *page)
{
VM_BUG_ON_PAGE(!PageCompound(page), page);
@@ -801,10 +806,16 @@ static inline void page_mapcount_reset(struct page *page)
int __page_mapcount(struct page *page);
+/*
+ * Mapcount of 0-order page; when compound sub-page, includes
+ * compound_mapcount().
+ *
+ * Result is undefined for pages which cannot be mapped into userspace.
+ * For example SLAB or special types of pages. See function page_has_type().
+ * They use this place in struct page differently.
+ */
static inline int page_mapcount(struct page *page)
{
- VM_BUG_ON_PAGE(PageSlab(page), page);
-
if (unlikely(PageCompound(page)))
return __page_mapcount(page);
return atomic_read(&page->_mapcount) + 1;