Index: sys/cddl/compat/opensolaris/kern/opensolaris_kmem.c
===================================================================
--- sys/cddl/compat/opensolaris/kern/opensolaris_kmem.c	(revision 270422)
+++ sys/cddl/compat/opensolaris/kern/opensolaris_kmem.c	(working copy)
@@ -126,18 +126,47 @@ kmem_size_init(void *unused __unused)
 }
 SYSINIT(kmem_size_init, SI_SUB_KMEM, SI_ORDER_ANY, kmem_size_init, NULL);
 
-uint64_t
-kmem_size(void)
+/*
+ * The return values from kmem_free_* are only valid once the pagedaemon
+ * has been initialised, before then they return 0.
+ * 
+ * To ensure the returns are valid the caller can use a SYSINIT with
+ * subsystem set to SI_SUB_KTHREAD_PAGE and an order of at least
+ * SI_ORDER_SECOND.
+ */
+u_int
+kmem_free_target(void)
 {
 
-	return (kmem_size_val);
+	return (cnt.v_free_target);
 }
 
+u_int
+kmem_free_min(void)
+{
+
+	return (cnt.v_free_min);
+}
+
+u_int
+kmem_free_count(void)
+{
+
+	return (cnt.v_free_count);
+}
+
+u_int
+kmem_page_count(void)
+{
+
+	return (cnt.v_page_count);
+}
+
 uint64_t
-kmem_used(void)
+kmem_size(void)
 {
 
-	return (vmem_size(kmem_arena, VMEM_ALLOC));
+	return (kmem_size_val);
 }
 
 static int
Index: sys/cddl/compat/opensolaris/sys/kmem.h
===================================================================
--- sys/cddl/compat/opensolaris/sys/kmem.h	(revision 270422)
+++ sys/cddl/compat/opensolaris/sys/kmem.h	(working copy)
@@ -66,7 +66,16 @@ typedef struct kmem_cache {
 void *zfs_kmem_alloc(size_t size, int kmflags);
 void zfs_kmem_free(void *buf, size_t size);
 uint64_t kmem_size(void);
-uint64_t kmem_used(void);
+u_int kmem_page_count(void);
+
+/*
+ * The return values from kmem_free_* are only valid once the pagedaemon
+ * has been initialised, before then they return 0.
+ */
+u_int kmem_free_count(void);
+u_int kmem_free_target(void);
+u_int kmem_free_min(void);
+
 kmem_cache_t *kmem_cache_create(char *name, size_t bufsize, size_t align,
     int (*constructor)(void *, void *, int), void (*destructor)(void *, void *),
     void (*reclaim)(void *) __unused, void *private, vmem_t *vmp, int cflags);
Index: sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
===================================================================
--- sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c	(revision 270422)
+++ sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c	(working copy)
@@ -193,9 +193,6 @@ extern int zfs_prefetch_disable;
  */
 static boolean_t arc_warm;
 
-/*
- * These tunables are for performance analysis.
- */
 uint64_t zfs_arc_max;
 uint64_t zfs_arc_min;
 uint64_t zfs_arc_meta_limit = 0;
@@ -204,10 +201,24 @@ int zfs_arc_shrink_shift = 0;
 int zfs_arc_p_min_shift = 0;
 int zfs_disable_dup_eviction = 0;
 uint64_t zfs_arc_average_blocksize = 8 * 1024; /* 8KB */
+u_int zfs_arc_free_target = (1 << 19); /* default before pagedaemon init only */
 
+static int sysctl_vfs_zfs_arc_free_target(SYSCTL_HANDLER_ARGS);
+
+#ifdef _KERNEL
+static void
+arc_free_target_init(void *unused __unused)
+{
+
+	zfs_arc_free_target = kmem_free_target();
+}
+SYSINIT(arc_free_target_init, SI_SUB_KTHREAD_PAGE, SI_ORDER_ANY,
+    arc_free_target_init, NULL);
+#endif
+
 TUNABLE_QUAD("vfs.zfs.arc_max", &zfs_arc_max);
 TUNABLE_QUAD("vfs.zfs.arc_min", &zfs_arc_min);
 TUNABLE_QUAD("vfs.zfs.arc_meta_limit", &zfs_arc_meta_limit);
 TUNABLE_QUAD("vfs.zfs.arc_average_blocksize", &zfs_arc_average_blocksize);
 SYSCTL_DECL(_vfs_zfs);
 SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, arc_max, CTLFLAG_RDTUN, &zfs_arc_max, 0,
@@ -217,7 +228,36 @@ SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, arc_min, CTLFLAG_
 SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, arc_average_blocksize, CTLFLAG_RDTUN,
     &zfs_arc_average_blocksize, 0,
     "ARC average blocksize");
+/*
+ * We don't have a tunable for arc_free_target due to the dependency on
+ * pagedaemon initialisation.
+ */
+SYSCTL_PROC(_vfs_zfs, OID_AUTO, arc_free_target,
+    CTLTYPE_UINT | CTLFLAG_MPSAFE | CTLFLAG_RW, 0, sizeof(u_int),
+    sysctl_vfs_zfs_arc_free_target, "IU",
+    "Desired number of free pages below which ARC triggers reclaim");
 
+static int
+sysctl_vfs_zfs_arc_free_target(SYSCTL_HANDLER_ARGS)
+{
+	u_int val;
+	int err;
+
+	val = zfs_arc_free_target;
+	err = sysctl_handle_int(oidp, &val, 0, req);
+	if (err != 0 || req->newptr == NULL)
+		return (err);
+
+	if (val < kmem_free_min())
+		return (EINVAL);
+	if (val > kmem_page_count())
+		return (EINVAL);
+
+	zfs_arc_free_target = val;
+
+	return (0);
+}
+
 /*
  * Note that buffers can be in one of 6 states:
  *	ARC_anon	- anonymous (discussed below)
@@ -2421,9 +2461,12 @@ arc_flush(spa_t *spa)
 void
 arc_shrink(void)
 {
+
 	if (arc_c > arc_c_min) {
 		uint64_t to_free;
 
+		DTRACE_PROBE2(arc__shrink, uint64_t, arc_c, uint64_t,
+			arc_c_min);
 #ifdef _KERNEL
 		to_free = arc_c >> arc_shrink_shift;
 #else
@@ -2443,8 +2486,11 @@ arc_shrink(void)
 		ASSERT((int64_t)arc_p >= 0);
 	}
 
-	if (arc_size > arc_c)
+	if (arc_size > arc_c) {
+		DTRACE_PROBE2(arc__shrink_adjust, uint64_t, arc_size,
+			uint64_t, arc_c);
 		arc_adjust();
+	}
 }
 
 static int needfree = 0;
@@ -2455,15 +2501,25 @@ arc_reclaim_needed(void)
 
 #ifdef _KERNEL
 
-	if (needfree)
+	if (needfree) {
+		DTRACE_PROBE(arc__reclaim_needfree);
 		return (1);
+	}
 
+	if (kmem_free_count() < zfs_arc_free_target) {
+		DTRACE_PROBE2(arc__reclaim_freetarget, uint64_t,
+		    kmem_free_count(), uint64_t, zfs_arc_free_target);
+		return (1);
+	}
+
 	/*
 	 * Cooperate with pagedaemon when it's time for it to scan
 	 * and reclaim some pages.
 	 */
-	if (vm_paging_needed())
+	if (vm_paging_needed()) {
+		DTRACE_PROBE(arc__reclaim_paging);
 		return (1);
+	}
 
 #ifdef sun
 	/*
@@ -2507,9 +2563,6 @@ arc_reclaim_needed(void)
 	    (btop(vmem_size(heap_arena, VMEM_FREE | VMEM_ALLOC)) >> 2))
 		return (1);
 #endif
-#else	/* !sun */
-	if (kmem_used() > (kmem_size() * 3) / 4)
-		return (1);
 #endif	/* sun */
 
 #else
@@ -2516,6 +2569,8 @@ arc_reclaim_needed(void)
 	if (spa_get_random(100) == 0)
 		return (1);
 #endif
+	DTRACE_PROBE(arc__reclaim_no);
+
 	return (0);
 }
 
Index: sys/vm/vm_pageout.c
===================================================================
--- sys/vm/vm_pageout.c	(revision 270422)
+++ sys/vm/vm_pageout.c	(working copy)
@@ -115,10 +115,14 @@ __FBSDID("$FreeBSD$");
 
 /* the kernel process "vm_pageout"*/
 static void vm_pageout(void);
+static void vm_pageout_init(void);
 static int vm_pageout_clean(vm_page_t);
 static void vm_pageout_scan(struct vm_domain *vmd, int pass);
 static void vm_pageout_mightbe_oom(struct vm_domain *vmd, int pass);
 
+SYSINIT(pagedaemon_init, SI_SUB_KTHREAD_PAGE, SI_ORDER_FIRST, vm_pageout_init,
+    NULL);
+
 struct proc *pageproc;
 
 static struct kproc_desc page_kp = {
@@ -126,7 +130,7 @@ static struct kproc_desc page_kp = {
 	vm_pageout,
 	&pageproc
 };
-SYSINIT(pagedaemon, SI_SUB_KTHREAD_PAGE, SI_ORDER_FIRST, kproc_start,
+SYSINIT(pagedaemon, SI_SUB_KTHREAD_PAGE, SI_ORDER_SECOND, kproc_start,
     &page_kp);
 
 #if !defined(NO_SWAPPING)
@@ -1637,15 +1641,11 @@ vm_pageout_worker(void *arg)
 }
 
 /*
- *	vm_pageout is the high level pageout daemon.
+ *	vm_pageout_init initialises basic pageout daemon settings.
  */
 static void
-vm_pageout(void)
+vm_pageout_init(void)
 {
-#if MAXMEMDOM > 1
-	int error, i;
-#endif
-
 	/*
 	 * Initialize some paging parameters.
 	 */
@@ -1691,7 +1691,18 @@ static void
 	/* XXX does not really belong here */
 	if (vm_page_max_wired == 0)
 		vm_page_max_wired = cnt.v_free_count / 3;
+}
 
+/*
+ *     vm_pageout is the high level pageout daemon.
+ */
+static void
+vm_pageout(void)
+{
+#if MAXMEMDOM > 1
+	int error, i;
+#endif
+
 	swap_pager_swap_init();
 #if MAXMEMDOM > 1
 	for (i = 1; i < vm_ndomains; i++) {