mm: rework mapcount accounting to enable 4k mapping of THPs

[cascardo/linux.git] / include / linux / mm.h

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 70f59de..67e0fab 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -410,6 +410,19 @@ static inline int is_vmalloc_or_module_addr(const void *x)
 
 extern void kvfree(const void *addr);
 
+static inline atomic_t *compound_mapcount_ptr(struct page *page)
+{
+       return &page[1].compound_mapcount;
+}
+
+static inline int compound_mapcount(struct page *page)
+{
+       if (!PageCompound(page))
+               return 0;
+       page = compound_head(page);
+       return atomic_read(compound_mapcount_ptr(page)) + 1;
+}
+
 /*
  * The atomic page->_mapcount, starts from -1: so that transitions
  * both from it and to it can be tracked, using atomic_inc_and_test
@@ -422,8 +435,17 @@ static inline void page_mapcount_reset(struct page *page)
 
 static inline int page_mapcount(struct page *page)
 {
+       int ret;
        VM_BUG_ON_PAGE(PageSlab(page), page);
-       return atomic_read(&page->_mapcount) + 1;
+
+       ret = atomic_read(&page->_mapcount) + 1;
+       if (PageCompound(page)) {
+               page = compound_head(page);
+               ret += atomic_read(compound_mapcount_ptr(page)) + 1;
+               if (PageDoubleMap(page))
+                       ret--;
+       }
+       return ret;
 }
 
 static inline int page_count(struct page *page)
@@ -934,7 +956,7 @@ static inline pgoff_t page_file_index(struct page *page)
  */
 static inline int page_mapped(struct page *page)
 {
-       return atomic_read(&(page)->_mapcount) >= 0;
+       return atomic_read(&(page)->_mapcount) + compound_mapcount(page) >= 0;
 }
 
 /*