diff --git a/sys/kern/kern_mbuf.c b/sys/kern/kern_mbuf.c
index 0f999247aa1..39349654b50 100644
--- a/sys/kern/kern_mbuf.c
+++ b/sys/kern/kern_mbuf.c
@@ -372,6 +372,14 @@ mb_dtor_pack(void *mem, int size, void *arg)
 #ifdef INVARIANTS
 	trash_dtor(m->m_ext.ext_buf, MCLBYTES, arg);
 #endif
+	/*
+	 * If there are processes blocked on zone_clust, waiting for pages to be freed up,
+	 * cause them to be woken up by draining the packet zone. We are exposed to a race here 
+	 * (in the check for the UMA_ZFLAG_FULL) where we might miss the flag set, but that is 
+	 * deliberate. We don't want to acquire the zone lock for every mbuf free.
+	 */
+ 	if (uma_zone_exhausted_nolock(zone_clust))
+ 		zone_drain(zone_pack);
 }
 
 /*
diff --git a/sys/sys/mbuf.h b/sys/sys/mbuf.h
index 13e7e7f9ff9..bfb82be44c3 100644
--- a/sys/sys/mbuf.h
+++ b/sys/sys/mbuf.h
@@ -457,6 +457,14 @@ m_clget(struct mbuf *m, int how)
 		printf("%s: %p mbuf already has cluster\n", __func__, m);
 	m->m_ext.ext_buf = (char *)NULL;
 	uma_zalloc_arg(zone_clust, m, how);
+	/*
+	 * On a cluster allocation failure, drain the packet zone and retry,
+	 * we might be able to loosen a few clusters up on the drain.
+	 */
+	if ((how & M_NOWAIT) && (m->m_ext.ext_buf == NULL)) {
+		zone_drain(zone_pack);
+		uma_zalloc_arg(zone_clust, m, how);
+	}
 }
 
 /*
diff --git a/sys/vm/uma.h b/sys/vm/uma.h
index 08a55d675e8..00271772336 100644
--- a/sys/vm/uma.h
+++ b/sys/vm/uma.h
@@ -48,6 +48,8 @@ struct uma_zone;
 /* Opaque type used as a handle to the zone */
 typedef struct uma_zone * uma_zone_t;
 
+void zone_drain(uma_zone_t);
+
 /* 
  * Item constructor
  *
@@ -518,6 +520,7 @@ u_int32_t *uma_find_refcnt(uma_zone_t zone, void *item);
  * 	Non-zero if zone is exhausted.
  */
 int uma_zone_exhausted(uma_zone_t zone);
+int uma_zone_exhausted_nolock(uma_zone_t zone);
 
 /*
  * Exported statistics structures to be used by user space monitoring tools.
diff --git a/sys/vm/uma_core.c b/sys/vm/uma_core.c
index 62e7aff5af6..fa2cb05f7e3 100644
--- a/sys/vm/uma_core.c
+++ b/sys/vm/uma_core.c
@@ -238,7 +238,6 @@ static void bucket_zone_drain(void);
 static int uma_zalloc_bucket(uma_zone_t zone, int flags);
 static uma_slab_t uma_zone_slab(uma_zone_t zone, int flags);
 static void *uma_slab_alloc(uma_zone_t zone, uma_slab_t slab);
-static void zone_drain(uma_zone_t);
 static uma_zone_t uma_kcreate(uma_zone_t zone, size_t size, uma_init uminit,
     uma_fini fini, int align, u_int32_t flags);
 
@@ -680,7 +679,7 @@ bucket_cache_drain(uma_zone_t zone)
  * Returns:
  *	Nothing.
  */
-static void
+void
 zone_drain(uma_zone_t zone)
 {
 	struct slabhead freeslabs = { 0 };
@@ -2679,6 +2678,12 @@ uma_zone_exhausted(uma_zone_t zone)
 	return (full);	
 }
 
+int
+uma_zone_exhausted_nolock(uma_zone_t zone)
+{
+	return (zone->uz_keg->uk_flags & UMA_ZFLAG_FULL);
+}
+
 void *
 uma_large_malloc(int size, int wait)
 {