fs/mpage.c: factor clean_buffers() out of __mpage_writepage()

__mpage_writepage() is over 200 lines long, has 20 local variables, four
goto labels and could desperately use simplification.  Splitting
clean_buffers() into a helper function improves matters a little,
removing 20+ lines from it.

Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Dheeraj Reddy <dheeraj.reddy@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/mpage.c

@@ -439,6 +439,35 @@ struct mpage_data {
 	unsigned use_writepage;
 };
 
+/*
+ * We have our BIO, so we can now mark the buffers clean.  Make
+ * sure to only clean buffers which we know we'll be writing.
+ */
+static void clean_buffers(struct page *page, unsigned first_unmapped)
+{
+	unsigned buffer_counter = 0;
+	struct buffer_head *bh, *head;
+	if (!page_has_buffers(page))
+		return;
+	head = page_buffers(page);
+	bh = head;
+
+	do {
+		if (buffer_counter++ == first_unmapped)
+			break;
+		clear_buffer_dirty(bh);
+		bh = bh->b_this_page;
+	} while (bh != head);
+
+	/*
+	 * we cannot drop the bh if the page is not uptodate or a concurrent
+	 * readpage would fail to serialize with the bh and it would read from
+	 * disk before we reach the platter.
+	 */
+	if (buffer_heads_over_limit && PageUptodate(page))
+		try_to_free_buffers(page);
+}
+
 static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
 		      void *data)
 {
@@ -591,30 +620,7 @@ alloc_new:
 		goto alloc_new;
 	}
 
-	/*
-	 * OK, we have our BIO, so we can now mark the buffers clean.  Make
-	 * sure to only clean buffers which we know we'll be writing.
-	 */
-	if (page_has_buffers(page)) {
-		struct buffer_head *head = page_buffers(page);
-		struct buffer_head *bh = head;
-		unsigned buffer_counter = 0;
-
-		do {
-			if (buffer_counter++ == first_unmapped)
-				break;
-			clear_buffer_dirty(bh);
-			bh = bh->b_this_page;
-		} while (bh != head);
-
-		/*
-		 * we cannot drop the bh if the page is not uptodate
-		 * or a concurrent readpage would fail to serialize with the bh
-		 * and it would read from disk before we reach the platter.
-		 */
-		if (buffer_heads_over_limit && PageUptodate(page))
-			try_to_free_buffers(page);
-	}
+	clean_buffers(page, first_unmapped);
 
 	BUG_ON(PageWriteback(page));
 	set_page_writeback(page);