[PATCH] revert writeback threshold changes

The post-2.6.8 recent tweaks to the page writeback thresholding code seems to
be doing the wrong thing for small unmapped_ratios - nathans had a few
problems with it.  The problem it was trying to fix is minor and fairly
theoretical anyway, so back it out to the old code.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/page-writeback.c

@@ -153,11 +153,9 @@ get_dirty_limits(struct writeback_state *wbs, long *pbackground, long *pdirty)
 	if (dirty_ratio < 5)
 		dirty_ratio = 5;
 
-	/*
-	 * Keep the ratio between dirty_ratio and background_ratio roughly
-	 * what the sysctls are after dirty_ratio has been scaled (above).
-	 */
-	background_ratio = dirty_background_ratio * dirty_ratio/vm_dirty_ratio;
+	background_ratio = dirty_background_ratio;
+	if (background_ratio >= dirty_ratio)
+		background_ratio = dirty_ratio / 2;
 
 	background = (background_ratio * total_pages) / 100;
 	dirty = (dirty_ratio * total_pages) / 100;