Clean up __page_set_anon_rmap

Linus asked for a cleanup of __page_set_anon_rmap to make
it look more like the cleaner huge pages version.

Factor out the duplicated PageAnon check into a single check
at the beginning of the function.

Remove obsolete comments and rewrite them into standard English.

No functional changes.
Signed-off-by: Andi Kleen <ak@linux.intel.com>

mm/rmap.c

@@ -780,10 +780,10 @@ void page_move_anon_rmap(struct page *page,
 }
 
 /**
- * __page_set_anon_rmap - setup new anonymous rmap
- * @page:	the page to add the mapping to
- * @vma:	the vm area in which the mapping is added
- * @address:	the user virtual address mapped
+ * __page_set_anon_rmap - set up new anonymous rmap
+ * @page:	Page to add to rmap	
+ * @vma:	VM area to add page to.
+ * @address:	User virtual address of the mapping	
  * @exclusive:	the page is exclusively owned by the current process
  */
 static void __page_set_anon_rmap(struct page *page,
@@ -793,25 +793,16 @@ static void __page_set_anon_rmap(struct page *page,
 
 	BUG_ON(!anon_vma);
 
+	if (PageAnon(page))
+		return;
+
 	/*
 	 * If the page isn't exclusively mapped into this vma,
 	 * we must use the _oldest_ possible anon_vma for the
 	 * page mapping!
 	 */
-	if (!exclusive) {
-		if (PageAnon(page))
-			return;
+	if (!exclusive)
 		anon_vma = anon_vma->root;
-	} else {
-		/*
-		 * In this case, swapped-out-but-not-discarded swap-cache
-		 * is remapped. So, no need to update page->mapping here.
-		 * We convice anon_vma poitned by page->mapping is not obsolete
-		 * because vma->anon_vma is necessary to be a family of it.
-		 */
-		if (PageAnon(page))
-			return;
-	}
 
 	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
 	page->mapping = (struct address_space *) anon_vma;