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.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

---
Changes since -v8:
 - initialized init_task

 - moved the prop_local init after the task_struct copy

 - changed the per task ratio to 1/8 (from 1/2).

 - explicit usage of prop_local_single
 include/linux/init_task.h |    1

 include/linux/sched.h     |    2 +

 kernel/fork.c             |   10 +++++++++

 mm/page-writeback.c       |   50 +++++++++++++++++++++++++++++++++++++++++++++-

 4 files changed, 62 insertions(+), 1 deletion(-)
Index: linux-2.6/include/linux/sched.h

===================================================================

--- linux-2.6.orig/include/linux/sched.h

+++ linux-2.6/include/linux/sched.h

@@ -84,6 +84,7 @@ struct sched_param {

 #include <linux/timer.h>

 #include <linux/hrtimer.h>

 #include <linux/task_io_accounting.h>

+#include <linux/proportions.h>
 #include <asm/processor.h>
@@ -1125,6 +1126,7 @@ struct task_struct {

 #ifdef CONFIG_FAULT_INJECTION

 	int make_it_fail;

 #endif

+	struct prop_local_single dirties;

 };
 /*

Index: linux-2.6/kernel/fork.c

===================================================================

--- linux-2.6.orig/kernel/fork.c

+++ linux-2.6/kernel/fork.c

@@ -107,6 +107,7 @@ static struct kmem_cache *mm_cachep;
 void free_task(struct task_struct *tsk)

 {

+	prop_local_destroy_single(&tsk->dirties);

 	free_thread_info(tsk->stack);

 	rt_mutex_debug_task_free(tsk);

 	free_task_struct(tsk);

@@ -163,6 +164,...
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