--- a/src/hotspot/share/runtime/arguments.cpp	Wed Nov 14 09:19:31 2018 +0100
+++ b/src/hotspot/share/runtime/arguments.cpp	Wed Nov 14 04:56:43 2018 -0500
@@ -2642,23 +2642,7 @@
       // Obsolete in JDK 10
       JDK_Version::jdk(10).to_string(version, sizeof(version));
       warning("Ignoring option %s; support was removed in %s", option->optionString, version);
-    // -Xconcurrentio
-    } else if (match_option(option, "-Xconcurrentio")) {
-      if (FLAG_SET_CMDLINE(bool, UseLWPSynchronization, true) != JVMFlag::SUCCESS) {
-        return JNI_EINVAL;
-      }
-      if (FLAG_SET_CMDLINE(bool, BackgroundCompilation, false) != JVMFlag::SUCCESS) {
-        return JNI_EINVAL;
-      }
-      SafepointSynchronize::set_defer_thr_suspend_loop_count();
-      if (FLAG_SET_CMDLINE(bool, UseTLAB, false) != JVMFlag::SUCCESS) {
-        return JNI_EINVAL;
-      }
-      if (FLAG_SET_CMDLINE(size_t, NewSizeThreadIncrease, 16 * K) != JVMFlag::SUCCESS) {  // 20Kb per thread added to new generation
-        return JNI_EINVAL;
-      }
-
-      // -Xinternalversion
+    // -Xinternalversion
     } else if (match_option(option, "-Xinternalversion")) {
       jio_fprintf(defaultStream::output_stream(), "%s\n",
                   VM_Version::internal_vm_info_string());

--- a/src/hotspot/share/runtime/safepoint.hpp	Wed Nov 14 09:19:31 2018 +0100
+++ b/src/hotspot/share/runtime/safepoint.hpp	Wed Nov 14 04:56:43 2018 -0500
@@ -178,10 +178,6 @@
 
   static address safepoint_counter_addr()                  { return (address)&_safepoint_counter; }
 
-  // This method is only used for -Xconcurrentio support.
-  static void set_defer_thr_suspend_loop_count() {
-    _defer_thr_suspend_loop_count = 1;
-  }
 };
 
 // Some helper assert macros for safepoint checks.

--- a/test/hotspot/jtreg/runtime/CommandLine/TestNullTerminatedFlags.java	Wed Nov 14 09:19:31 2018 +0100
+++ b/test/hotspot/jtreg/runtime/CommandLine/TestNullTerminatedFlags.java	Wed Nov 14 04:56:43 2018 -0500
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2018, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -42,7 +42,6 @@
             "-green",
             "-native",
             "-Xrs",
-            "-Xconcurrentio",
             "-Xinternalversion",
             "-Xprintflags",
             "-Xint",