diff --git a/share/man/man9/zone.9 b/share/man/man9/zone.9
--- a/share/man/man9/zone.9
+++ b/share/man/man9/zone.9
@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd April 14, 2021
+.Dd February 15, 2022
 .Dt UMA 9
 .Os
 .Sh NAME
@@ -324,6 +324,12 @@
 Items in this zone must be contiguous in physical address space.
 Items will follow normal alignment constraints and may span page boundaries
 between pages with contiguous physical addresses.
+.It Dv UMA_ZONE_UNMANAGED
+By default, UMA zone caches are shrunk to help resolve free page shortages.
+Cached items that have not been used for a long period may also be freed from
+zone.
+When this flag is set, the system will not reclaim memory from the zone's
+caches.
 .El
 .Pp
 Zones can be destroyed using
diff --git a/sys/vm/uma.h b/sys/vm/uma.h
--- a/sys/vm/uma.h
+++ b/sys/vm/uma.h
@@ -233,6 +233,10 @@
  * These flags share space with UMA_ZFLAGs in uma_int.h.  Be careful not to
  * overlap when adding new features.
  */
+#define	UMA_ZONE_UNMANAGED	0x0001	/*
+					 * Don't regulate the cache size, even
+					 * under memory pressure.
+					 */
 #define UMA_ZONE_ZINIT		0x0002	/* Initialize with zeros */
 #define UMA_ZONE_CONTIG		0x0004	/*
 					 * Physical memory underlying an object
diff --git a/sys/vm/uma_core.c b/sys/vm/uma_core.c
--- a/sys/vm/uma_core.c
+++ b/sys/vm/uma_core.c
@@ -1223,10 +1223,12 @@
 
 trim:
 	/* Trim caches not used for a long time. */
-	for (int i = 0; i < vm_ndomains; i++) {
-		if (bucket_cache_reclaim_domain(zone, false, false, i) &&
-		    (zone->uz_flags & UMA_ZFLAG_CACHE) == 0)
-			keg_drain(zone->uz_keg, i);
+	if ((zone->uz_flags & UMA_ZONE_UNMANAGED) == 0) {
+		for (int i = 0; i < vm_ndomains; i++) {
+			if (bucket_cache_reclaim_domain(zone, false, false, i) &&
+			    (zone->uz_flags & UMA_ZFLAG_CACHE) == 0)
+				keg_drain(zone->uz_keg, i);
+		}
 	}
 }
 
@@ -1735,24 +1737,6 @@
 	ZONE_UNLOCK(zone);
 }
 
-static void
-zone_drain(uma_zone_t zone, void *arg)
-{
-	int domain;
-
-	domain = (int)(uintptr_t)arg;
-	zone_reclaim(zone, domain, M_NOWAIT, true);
-}
-
-static void
-zone_trim(uma_zone_t zone, void *arg)
-{
-	int domain;
-
-	domain = (int)(uintptr_t)arg;
-	zone_reclaim(zone, domain, M_NOWAIT, false);
-}
-
 /*
  * Allocate a new slab for a keg and inserts it into the partial slab list.
  * The keg should be unlocked on entry.  If the allocation succeeds it will
@@ -3548,7 +3532,8 @@
 			    zone->uz_ctor(item, zone->uz_size, udata,
 			    flags) != 0) {
 				counter_u64_add(zone->uz_fails, 1);
-			    	zone->uz_fini(item, zone->uz_size);
+				if (zone->uz_fini != NULL)
+					zone->uz_fini(item, zone->uz_size);
 				*itemp = NULL;
 				return (error);
 			}
@@ -5202,6 +5187,21 @@
 	return (sz * PAGE_SIZE);
 }
 
+struct uma_reclaim_args {
+	int	domain;
+	int	req;
+};
+
+static void
+uma_reclaim_domain_cb(uma_zone_t zone, void *arg)
+{
+	struct uma_reclaim_args *args;
+
+	args = arg;
+	if ((zone->uz_flags & UMA_ZONE_UNMANAGED) == 0)
+		uma_zone_reclaim_domain(zone, args->req, args->domain);
+}
+
 /* See uma.h */
 void
 uma_reclaim(int req)
@@ -5212,23 +5212,23 @@
 void
 uma_reclaim_domain(int req, int domain)
 {
-	void *arg;
+	struct uma_reclaim_args args;
 
 	bucket_enable();
 
-	arg = (void *)(uintptr_t)domain;
+	args.domain = domain;
+	args.req = req;
+
 	sx_slock(&uma_reclaim_lock);
 	switch (req) {
 	case UMA_RECLAIM_TRIM:
-		zone_foreach(zone_trim, arg);
-		break;
 	case UMA_RECLAIM_DRAIN:
-		zone_foreach(zone_drain, arg);
+		zone_foreach(uma_reclaim_domain_cb, &args);
 		break;
 	case UMA_RECLAIM_DRAIN_CPU:
-		zone_foreach(zone_drain, arg);
+		zone_foreach(uma_reclaim_domain_cb, &args);
 		pcpu_cache_drain_safe(NULL);
-		zone_foreach(zone_drain, arg);
+		zone_foreach(uma_reclaim_domain_cb, &args);
 		break;
 	default:
 		panic("unhandled reclamation request %d", req);
@@ -5239,8 +5239,8 @@
 	 * we visit again so that we can free pages that are empty once other
 	 * zones are drained.  We have to do the same for buckets.
 	 */
-	zone_drain(slabzones[0], arg);
-	zone_drain(slabzones[1], arg);
+	uma_zone_reclaim_domain(slabzones[0], UMA_RECLAIM_DRAIN, domain);
+	uma_zone_reclaim_domain(slabzones[1], UMA_RECLAIM_DRAIN, domain);
 	bucket_zone_drain(domain);
 	sx_sunlock(&uma_reclaim_lock);
 }
@@ -5283,19 +5283,16 @@
 void
 uma_zone_reclaim_domain(uma_zone_t zone, int req, int domain)
 {
-	void *arg;
-
-	arg = (void *)(uintptr_t)domain;
 	switch (req) {
 	case UMA_RECLAIM_TRIM:
-		zone_trim(zone, arg);
+		zone_reclaim(zone, domain, M_NOWAIT, false);
 		break;
 	case UMA_RECLAIM_DRAIN:
-		zone_drain(zone, arg);
+		zone_reclaim(zone, domain, M_NOWAIT, true);
 		break;
 	case UMA_RECLAIM_DRAIN_CPU:
 		pcpu_cache_drain_safe(zone);
-		zone_drain(zone, arg);
+		zone_reclaim(zone, domain, M_NOWAIT, true);
 		break;
 	default:
 		panic("unhandled reclamation request %d", req);