mm: dirty balancing for tasks

Based on ideas of Andrew:
  http://marc.info/?l=linux-kernel&m=102912915020543&w=2

Scale the bdi dirty limit inversly with the tasks dirty rate.
This makes heavy writers have a lower dirty limit than the occasional writer.

Andrea proposed something similar:
  http://lwn.net/Articles/152277/

The main disadvantage to his patch is that he uses an unrelated quantity to
measure time, which leaves him with a workload dependant tunable. Other than
that the two approaches appear quite similar.

[akpm@linux-foundation.org: fix warning]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 513bc3e..3a619f5 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -171,6 +171,7 @@
 		[PIDTYPE_PGID] = INIT_PID_LINK(PIDTYPE_PGID),		\
 		[PIDTYPE_SID]  = INIT_PID_LINK(PIDTYPE_SID),		\
 	},								\
+	.dirties = INIT_PROP_LOCAL_SINGLE(dirties),			\
 	INIT_TRACE_IRQFLAGS						\
 	INIT_LOCKDEP							\
 }
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 592e3a5..59738ef 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -74,6 +74,7 @@
 #include <linux/pid.h>
 #include <linux/percpu.h>
 #include <linux/topology.h>
+#include <linux/proportions.h>
 #include <linux/seccomp.h>
 #include <linux/rcupdate.h>
 #include <linux/futex.h>
@@ -1149,6 +1150,7 @@
 #ifdef CONFIG_FAULT_INJECTION
 	int make_it_fail;
 #endif
+	struct prop_local_single dirties;
 };
 
 /*