rootdir: init.rc: Adjust background dirty writeout policy

Signed-off-by: San Mehat <san@google.com>
diff --git a/rootdir/init.rc b/rootdir/init.rc
index e777970..5657f51 100644
--- a/rootdir/init.rc
+++ b/rootdir/init.rc
@@ -180,6 +180,10 @@
     # Set init its forked children's oom_adj.
     write /proc/1/oom_adj -16
 
+    # Tweak background writeout
+    write /proc/sys/vm/dirty_expire_centisecs 200
+    write /proc/sys/vm/dirty_background_ratio  5
+
     # Permissions for System Server and daemons.
     chown radio system /sys/android_power/state
     chown radio system /sys/android_power/request_state