HWPOISON: Add invalidate_inode_page

Add a simple way to invalidate a single page
This is just a refactoring of the truncate.c code.
Originally from Fengguang, modified by Andi Kleen.
Signed-off-by: Andi Kleen <ak@linux.intel.com>

include/linux/mm.h

@@ -796,6 +796,8 @@ extern int vmtruncate_range(struct inode * inode, loff_t offset, loff_t end);
 
 int truncate_inode_page(struct address_space *mapping, struct page *page);
 
+int invalidate_inode_page(struct page *page);
+
 #ifdef CONFIG_MMU
 extern int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 			unsigned long address, unsigned int flags);

mm/truncate.c

@@ -146,6 +146,24 @@ int truncate_inode_page(struct address_space *mapping, struct page *page)
 	return truncate_complete_page(mapping, page);
 }
 
+/*
+ * Safely invalidate one page from its pagecache mapping.
+ * It only drops clean, unused pages. The page must be locked.
+ *
+ * Returns 1 if the page is successfully invalidated, otherwise 0.
+ */
+int invalidate_inode_page(struct page *page)
+{
+	struct address_space *mapping = page_mapping(page);
+	if (!mapping)
+		return 0;
+	if (PageDirty(page) || PageWriteback(page))
+		return 0;
+	if (page_mapped(page))
+		return 0;
+	return invalidate_complete_page(mapping, page);
+}
+
 /**
  * truncate_inode_pages - truncate range of pages specified by start & end byte offsets
  * @mapping: mapping to truncate
@@ -312,12 +330,8 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
 			if (lock_failed)
 				continue;
 
-			if (PageDirty(page) || PageWriteback(page))
-				goto unlock;
-			if (page_mapped(page))
-				goto unlock;
-			ret += invalidate_complete_page(mapping, page);
-unlock:
+			ret += invalidate_inode_page(page);
+
 			unlock_page(page);
 			if (next > end)
 				break;