mm: bdi: allow setting a maximum for the bdi dirty limit

Add "max_ratio" to /sys/class/bdi.  This indicates the maximum percentage of
the global dirty threshold allocated to this bdi.

[mszeredi@suse.cz]

 - fix parsing in max_ratio_store().
 - export bdi_set_max_ratio() to modules
 - limit bdi_dirty with bdi->max_ratio
 - document new sysfs attribute

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/include/linux/proportions.h b/include/linux/proportions.h
index 2c3b3cad92be..5afc1b23346d 100644
--- a/include/linux/proportions.h
+++ b/include/linux/proportions.h
@@ -78,6 +78,19 @@ void prop_inc_percpu(struct prop_descriptor *pd, struct prop_local_percpu *pl)
 }
 
 /*
+ * Limit the time part in order to ensure there are some bits left for the
+ * cycle counter and fraction multiply.
+ */
+#define PROP_MAX_SHIFT (3*BITS_PER_LONG/4)
+
+#define PROP_FRAC_SHIFT         (BITS_PER_LONG - PROP_MAX_SHIFT - 1)
+#define PROP_FRAC_BASE          (1UL << PROP_FRAC_SHIFT)
+
+void __prop_inc_percpu_max(struct prop_descriptor *pd,
+                           struct prop_local_percpu *pl, long frac);
+
+
+/*
  * ----- SINGLE ------
  */