From e49471b04b4bf0bfc58e2feeb0dd4208ea8f7c0d Mon Sep 17 00:00:00 2001
From: Andre Oppermann <andre@FreeBSD.org>
Date: Mon, 16 Aug 2010 14:24:00 +0000
Subject: [PATCH] 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
---
 sys/vm/uma.h      | 12 ++++++++++++
 sys/vm/uma_core.c | 18 ++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/sys/vm/uma.h b/sys/vm/uma.h
index 2076d3bd0b61..f0522b01631d 100644
--- a/sys/vm/uma.h
+++ b/sys/vm/uma.h
@@ -458,6 +458,18 @@ 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
diff --git a/sys/vm/uma_core.c b/sys/vm/uma_core.c
index 2dcd14fdd1a3..558b4c727e75 100644
--- a/sys/vm/uma_core.c
+++ b/sys/vm/uma_core.c
@@ -2796,6 +2796,24 @@ uma_zone_set_max(uma_zone_t zone, int nitems)
 	ZONE_UNLOCK(zone);
 }
 
+/* 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)