Index: cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
===================================================================
--- cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
+++ cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
@@ -4290,6 +4290,7 @@
 	}
 
 #endif	/* illumos */
+#ifdef __FreeBSD__
 #if defined(__i386) || !defined(UMA_MD_SMALL_ALLOC)
 	/*
 	 * If we're on an i386 platform, it's possible that we'll exhaust the
@@ -4302,16 +4303,14 @@
 	 * heap is allocated.  (Or, in the calculation, if less than 1/4th is
 	 * free)
 	 */
-	n = (int64_t)vmem_size(heap_arena, VMEM_FREE) -
-	    (vmem_size(heap_arena, VMEM_FREE | VMEM_ALLOC) >> 2);
+	n = uma_avail() - (long)(uma_limit() / 4);
 	if (n < lowest) {
 		lowest = n;
 		r = FMR_HEAP_ARENA;
 	}
+#endif
 #define	zio_arena	NULL
-#else
-#define	zio_arena	heap_arena
-#endif
+#endif	/* __FreeBSD__ */
 
 	/*
 	 * If zio data pages are being allocated out of a separate heap segment,
@@ -4335,6 +4334,8 @@
 	 * Above limits know nothing about real level of KVA fragmentation.
 	 * Start aggressive reclamation if too little sequential KVA left.
 	 */
+#ifndef __FreeBSD__
+	/* FreeBSD will reclaim via a uma or vmem lowmem callback. */
 	if (lowest > 0) {
 		n = (vmem_size(heap_arena, VMEM_MAXFREE) < SPA_MAXBLOCKSIZE) ?
 		    -((int64_t)vmem_size(heap_arena, VMEM_ALLOC) >> 4) :
@@ -4344,6 +4345,7 @@
 			r = FMR_ZIO_FRAG;
 		}
 	}
+#endif
 
 #else	/* _KERNEL */
 	/* Every 100 calls, free a small amount */
@@ -6110,8 +6112,7 @@
 	static uint64_t last_txg = 0;
 
 #if defined(__i386) || !defined(UMA_MD_SMALL_ALLOC)
-	available_memory =
-	    MIN(available_memory, ptob(vmem_size(heap_arena, VMEM_FREE)));
+	available_memory = MIN(available_memory, uma_avail());
 #endif
 
 	if (freemem > (uint64_t)physmem * arc_lotsfree_percent / 100)
@@ -6492,9 +6493,13 @@
 	 * Metadata is stored in the kernel's heap.  Don't let us
 	 * use more than half the heap for the ARC.
 	 */
+#ifdef __FreeBSD__
+	arc_meta_limit = MIN(arc_meta_limit, uma_limit() / 2);
+#else
 	arc_meta_limit = MIN(arc_meta_limit,
 	    vmem_size(heap_arena, VMEM_ALLOC | VMEM_FREE) / 2);
 #endif
+#endif
 
 	/* Allow the tunable to override if it is reasonable */
 	if (zfs_arc_meta_limit > 0 && zfs_arc_meta_limit <= arc_c_max)
Index: vm/uma.h
===================================================================
--- vm/uma.h
+++ vm/uma.h
@@ -698,4 +698,12 @@
 void uma_reclaim_wakeup(void);
 void uma_reclaim_worker(void *);
 
+unsigned long uma_limit(void);
+
+/* Return the amount of memory managed by UMA. */
+unsigned long uma_size(void);
+
+/* Return the amount of memory remaining.  May be negative. */
+long uma_avail(void);
+
 #endif	/* _VM_UMA_H_ */
Index: vm/uma_core.c
===================================================================
--- vm/uma_core.c
+++ vm/uma_core.c
@@ -3265,9 +3265,16 @@
 uma_size(void)
 {
 
-	return uma_kmem_total;
+	return (uma_kmem_total);
 }
 
+long
+uma_avail(void)
+{
+
+	return (uma_kmem_limit - uma_kmem_total);
+}
+
 void
 uma_print_stats(void)
 {
Index: vm/uma_int.h
===================================================================
--- vm/uma_int.h
+++ vm/uma_int.h
@@ -428,10 +428,6 @@
 
 /* Set a global soft limit on UMA managed memory. */
 void uma_set_limit(unsigned long limit);
-unsigned long uma_limit(void);
-
-/* Return the amount of memory managed by UMA. */
-unsigned long uma_size(void);
 #endif /* _KERNEL */
 
 #endif /* VM_UMA_INT_H */