[PATCH] vm_dirty_ratio initialisation fix

When a system has a very large imbalance of overall memory size to
ZONE_NORMAL (for example when large amounts of numa remap space are in use)
page_writeback_init() may incorrectly set vm_dirty_ratio and
dirty_background_ratio to zero; leading to divide by zero errors elsewhere.
This patch bounds these at 1%.
Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/page-writeback.c

@@ -504,6 +504,11 @@ void __init page_writeback_init(void)
 		dirty_background_ratio /= 100;
 		vm_dirty_ratio *= correction;
 		vm_dirty_ratio /= 100;
+
+		if (dirty_background_ratio <= 0)
+			dirty_background_ratio = 1;
+		if (vm_dirty_ratio <= 0)
+			vm_dirty_ratio = 1;
 	}
 	mod_timer(&wb_timer, jiffies + (dirty_writeback_centisecs * HZ) / 100);
 	set_ratelimit();