--- old/make/autoconf/boot-jdk.m4	2018-04-13 15:16:29.408730515 +0200
+++ new/make/autoconf/boot-jdk.m4	2018-04-13 15:16:29.144731193 +0200
@@ -367,6 +367,8 @@
 
 AC_DEFUN_ONCE([BOOTJDK_SETUP_BOOT_JDK_ARGUMENTS],
 [
+  # Ensure OPENJDK_TARGET_CPU_ARCH has been setup
+  AC_REQUIRE([PLATFORM_SETUP_OPENJDK_BUILD_AND_TARGET])
   ##############################################################################
   #
   # Specify jvm options for anything that is run with the Boot JDK.
@@ -401,11 +403,20 @@
   AC_MSG_CHECKING([flags for boot jdk java command for big workloads])
 
   # Starting amount of heap memory.
-  ADD_JVM_ARG_IF_OK([-Xms64M],boot_jdk_jvmargs_big,[$JAVA])
-  BOOTCYCLE_JVM_ARGS_BIG=-Xms64M
+  if test "x$OPENJDK_TARGET_CPU_ARCH" = "xs390"; then
+    ADD_JVM_ARG_IF_OK([-Xms256M],boot_jdk_jvmargs_big,[$JAVA])
+    BOOTCYCLE_JVM_ARGS_BIG=-Xms256M
+  else
+    ADD_JVM_ARG_IF_OK([-Xms64M],boot_jdk_jvmargs_big,[$JAVA])
+    BOOTCYCLE_JVM_ARGS_BIG=-Xms64M
+  fi
 
   # Maximum amount of heap memory and stack size.
-  JVM_HEAP_LIMIT_32="1024"
+  if test "x$OPENJDK_TARGET_CPU_ARCH" = "xs390"; then
+    JVM_HEAP_LIMIT_32="768"
+  else
+    JVM_HEAP_LIMIT_32="1024"
+  fi
   # Running a 64 bit JVM allows for and requires a bigger heap
   JVM_HEAP_LIMIT_64="1600"
   STACK_SIZE_32=768