Index: usr.sbin/bsdinstall/scripts/zfsboot
===================================================================
--- usr.sbin/bsdinstall/scripts/zfsboot
+++ usr.sbin/bsdinstall/scripts/zfsboot
@@ -123,8 +123,22 @@
 #
 # How much swap to put on each block device in the boot pool
 # NOTE: Value passed to gpart(8); which supports SI unit suffixes.
-#
-: ${ZFSBOOT_SWAP_SIZE:=2g}
+# Keep algorithm in sync with SWAP_SIZE() in part_wizard.c.
+if [ -z "${ZFSBOOT_SWAP_SIZE}" ]; then
+	case $(sysctl -n hw.pagesize) in
+	65536)
+		pgs_per_gb=16384 ;;
+	16384)
+		pgs_per_gb=65536 ;;
+	4096|*)
+		pgs_per_gb=262144 ;;
+	esac
+	swap=$(($(sysctl -n hw.availpages) / $pg_per_gb / 20))
+	if [ $swap -lt 4 ]; then
+		swap=4
+	fi
+	ZFSBOOT_SWAP_SIZE=${swap}g
+fi
 
 #
 # Should we use geli(8) to encrypt the swap?