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, 32 insertions, 6 deletions

diff --git a/lib/proportions.c b/lib/proportions.c
index 9508d9a7af3e..4f387a643d72 100644
--- a/lib/proportions.c
+++ b/lib/proportions.c
@@ -73,12 +73,6 @@
 #include <linux/proportions.h>
 #include <linux/rcupdate.h>
 
-/*
- * Limit the time part in order to ensure there are some bits left for the
- * cycle counter.
- */
-#define PROP_MAX_SHIFT (3*BITS_PER_LONG/4)
-
 int prop_descriptor_init(struct prop_descriptor *pd, int shift)
 {
         int err;
@@ -268,6 +262,38 @@ void __prop_inc_percpu(struct prop_descriptor *pd, struct prop_local_percpu *pl)
 }
 
 /*
+ * identical to __prop_inc_percpu, except that it limits this pl's fraction to
+ * @frac/PROP_FRAC_BASE by ignoring events when this limit has been exceeded.
+ */
+void __prop_inc_percpu_max(struct prop_descriptor *pd,
+                           struct prop_local_percpu *pl, long frac)
+{
+        struct prop_global *pg = prop_get_global(pd);
+
+        prop_norm_percpu(pg, pl);
+
+        if (unlikely(frac != PROP_FRAC_BASE)) {
+                unsigned long period_2 = 1UL << (pg->shift - 1);
+                unsigned long counter_mask = period_2 - 1;
+                unsigned long global_count;
+                long numerator, denominator;
+
+                numerator = percpu_counter_read_positive(&pl->events);
+                global_count = percpu_counter_read(&pg->events);
+                denominator = period_2 + (global_count & counter_mask);
+
+                if (numerator > ((denominator * frac) >> PROP_FRAC_SHIFT))
+                        goto out_put;
+        }
+
+        percpu_counter_add(&pl->events, 1);
+        percpu_counter_add(&pg->events, 1);
+
+out_put:
+        prop_put_global(pd, pg);
+}
+
+/*
  * Obtain a fraction of this proportion
  *
  *   p_{j} = x_{j} / (period/2 + t % period/2)