[PATCH] real-time enhanced page allocator and throttling

From: Robert Love <rml@tech9.net>

- Let real-time tasks dip further into the reserves than usual in
  __alloc_pages().  There are a lot of ways to special case this.  This
  patch just cuts z->pages_low in half, before doing the incremental min
  thing, for real-time tasks.  I do not do anything in the low memory slow
  path.  We can be a _lot_ more aggressive if we want.  Right now, we just
  give real-time tasks a little help.

- Never ever call balance_dirty_pages() on a real-time task.  Where and
  how exactly we handle this is up for debate.  We could, for example,
  special case real-time tasks inside balance_dirty_pages().  This would
  allow us to perform some of the work (say, waking up pdflush) but not
  other work (say, the active throttling).  As it stands now, we do the
  per-processor accounting in balance_dirty_pages_ratelimited() but we
  never call balance_dirty_pages().  Lots of approaches work.  What we want
  to do is never engage the real-time task in forced writeback.

2 files changed, 3 insertions, 2 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 3c6e3129144d..3d9aba07d508 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -281,7 +281,9 @@ struct signal_struct {
 #define MAX_RT_PRIO		MAX_USER_RT_PRIO
 
 #define MAX_PRIO		(MAX_RT_PRIO + 40)
- 
+
+#define rt_task(p)		((p)->prio < MAX_RT_PRIO)
+
 /*
  * Some day this will be a full-fledged user tracking system..
  */
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 373e58fee2d4..1424811e1eab 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -84,7 +84,6 @@ int dirty_writeback_centisecs_handler(struct ctl_table *, int, struct file *,
 				      void __user *, size_t *);
 
 void page_writeback_init(void);
-void balance_dirty_pages(struct address_space *mapping);
 void balance_dirty_pages_ratelimited(struct address_space *mapping);
 int pdflush_operation(void (*fn)(unsigned long), unsigned long arg0);
 int do_writepages(struct address_space *mapping, struct writeback_control *wbc);