Add uma_zone_get_max() to obtain the effective limit after a call

to uma_zone_set_max().

The UMA zone limit is not exactly set to the value supplied but
rounded up to completely fill the backing store increment (a page
normally).  This can lead to surprising situations where the number
of elements allocated from UMA is higher than the supplied limit
value.  The new get function reads back the effective value so that
the supplied limit value can be adjusted to the real limit.

Reviewed by:	jeffr
MFC after:	1 week

2 files changed, 30 insertions, 0 deletions

diff --git a/sys/vm/uma.h b/sys/vm/uma.h
index 2076d3b..f0522b0 100644
--- a/sys/vm/uma.h
+++ b/sys/vm/uma.h
@@ -459,6 +459,18 @@ int uma_zone_set_obj(uma_zone_t zone, struct vm_object *obj, int size);
 void uma_zone_set_max(uma_zone_t zone, int nitems);
 
 /*
+ * Obtains the effective limit on the number of items in a zone
+ *
+ * Arguments:
+ *	zone  The zone to obtain the effective limit from
+ *
+ * Return:
+ *	0  No limit
+ *	int  The effective limit of the zone
+ */
+int uma_zone_get_max(uma_zone_t zone);
+
+/*
  * The following two routines (uma_zone_set_init/fini)
  * are used to set the backend init/fini pair which acts on an
  * object as it becomes allocated and is placed in a slab within
diff --git a/sys/vm/uma_core.c b/sys/vm/uma_core.c
index 2dcd14f..558b4c7 100644
--- a/sys/vm/uma_core.c
+++ b/sys/vm/uma_core.c
@@ -2797,6 +2797,24 @@ uma_zone_set_max(uma_zone_t zone, int nitems)
 }
 
 /* See uma.h */
+int
+uma_zone_get_max(uma_zone_t zone)
+{
+	int nitems;
+	uma_keg_t keg;
+
+	ZONE_LOCK(zone);
+	keg = zone_first_keg(zone);
+	if (keg->uk_maxpages)
+		nitems = keg->uk_maxpages * keg->uk_ipers;
+	else
+		nitems = 0;
+	ZONE_UNLOCK(zone);
+
+	return (nitems);
+}
+
+/* See uma.h */
 void
 uma_zone_set_init(uma_zone_t zone, uma_init uminit)
 {