mm/page-writeback.c: document bdi_min_ratio

Looks like someone got distracted after adding the comment characters.
Signed-off-by: Johannes Weiner <jweiner@redhat.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page-writeback.c

@@ -305,7 +305,9 @@ static unsigned long task_min_dirty_limit(unsigned long bdi_dirty)
 }
 
 /*
- *
+ * bdi_min_ratio keeps the sum of the minimum dirty shares of all
+ * registered backing devices, which, for obvious reasons, can not
+ * exceed 100%.
  */
 static unsigned int bdi_min_ratio;