[PATCH] writeback: initialize global_dirty_limit

[Fengguang Wu <fengguang.wu@intel.com>]

This prevents global_dirty_limit from remaining 0 (the initial value)
for long time, since it's only updated in update_dirty_limit() when
above the dirty freerun area.

It will avoid unexpected consequences when some random code use it as a
convenient approximation of the global dirty threshold.

Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
---
 mm/page-writeback.c |    1 +
 1 file changed, 1 insertion(+)

--- linux-next.orig/mm/page-writeback.c	2012-04-25 20:16:12.766859391 +0800
+++ linux-next/mm/page-writeback.c	2012-05-03 11:44:32.746272930 +0800
@@ -1568,6 +1568,7 @@ void writeback_set_ratelimit(void)
 	unsigned long background_thresh;
 	unsigned long dirty_thresh;
 	global_dirty_limits(&background_thresh, &dirty_thresh);
+	global_dirty_limit = dirty_thresh;
 	ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
 	if (ratelimit_pages < 16)
 		ratelimit_pages = 16;