fs: split off __alloc_page_buffers function

This splits off the __alloc_page_buffers() function from the
alloc_page_buffers_function(). In addition it adds a gfp_t parameter, so
the caller can specify the allocation flags.

Signed-off-by: Stefan Roesch <shr@fb.com>

fs/buffer.c

@@ -802,26 +802,13 @@ int remove_inode_buffers(struct inode *inode)
 	return ret;
 }
 
-/*
- * Create the appropriate buffers when given a page for data area and
- * the size of each buffer.. Use the bh->b_this_page linked list to
- * follow the buffers created.  Return NULL if unable to create more
- * buffers.
- *
- * The retry flag is used to differentiate async IO (paging, swapping)
- * which may not fail from ordinary buffer allocations.
- */
-struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
-		bool retry)
+struct buffer_head *__alloc_page_buffers(struct page *page, unsigned long size,
+		gfp_t gfp)
 {
 	struct buffer_head *bh, *head;
-	gfp_t gfp = GFP_NOFS | __GFP_ACCOUNT;
 	long offset;
 	struct mem_cgroup *memcg, *old_memcg;
 
-	if (retry)
-		gfp |= __GFP_NOFAIL;
-
 	/* The page lock pins the memcg */
 	memcg = page_memcg(page);
 	old_memcg = set_active_memcg(memcg);
@@ -859,6 +846,26 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
 
 	goto out;
 }
+
+/*
+ * Create the appropriate buffers when given a page for data area and
+ * the size of each buffer.. Use the bh->b_this_page linked list to
+ * follow the buffers created.  Return NULL if unable to create more
+ * buffers.
+ *
+ * The retry flag is used to differentiate async IO (paging, swapping)
+ * which may not fail from ordinary buffer allocations.
+ */
+struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
+		bool retry)
+{
+	gfp_t gfp = GFP_NOFS | __GFP_ACCOUNT;
+
+	if (retry)
+		gfp |= __GFP_NOFAIL;
+
+	return __alloc_page_buffers(page, size, gfp);
+}
 EXPORT_SYMBOL_GPL(alloc_page_buffers);
 
 static inline void