writeback: trace global_dirty_state

Add trace event balance_dirty_state for showing the global dirty page
counts and thresholds at each global_dirty_limits() invocation.  This
will cover the callers throttle_vm_writeout(), over_bground_thresh()
and each balance_dirty_pages() loop.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 798842a22474..f9d9f5476d58 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -447,6 +447,7 @@ void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
         }
         *pbackground = background;
         *pdirty = dirty;
+        trace_global_dirty_state(background, dirty);
 }
 
 /**