[PATCH 3/3] vm: writeout watermarks

[Nick Piggin]

3/3

--
SUSE Labs, Novell Inc.

Slightly change the writeout watermark calculations so we keep background
and synchronous writeout watermarks in the same ratios after adjusting them.
This ensures we should always attempt to start background writeout before
synchronous writeout.

Signed-off-by: Nick Piggin <npiggin@xxxxxxx>


Index: linux-2.6/mm/page-writeback.c
===================================================================
--- linux-2.6.orig/mm/page-writeback.c	2005-11-01 13:41:39.000000000 +1100
+++ linux-2.6/mm/page-writeback.c	2005-11-01 14:29:27.000000000 +1100
@@ -165,9 +165,11 @@ get_dirty_limits(struct writeback_state 
 	if (dirty_ratio < 5)
 		dirty_ratio = 5;
 
-	background_ratio = dirty_background_ratio;
-	if (background_ratio >= dirty_ratio)
-		background_ratio = dirty_ratio / 2;
+	/*
+	 * 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 = (background_ratio * available_memory) / 100;
 	dirty = (dirty_ratio * available_memory) / 100;