Summary

Deprecate the -XX:+TLABStats flag.

Problem

After the removal of the -XX:+FastTLABRefill flag in JDK-8194084 the -XX:+TLABStats flag no longer has any effect. It should be deprecated and eventually removed.

Solution

The TLABStats flag should be deprecated, meaning it will still be recognized but a warning will be generated at startup if it is specified on the command line.

Specification

Mark the flag as deprecated:

diff -r e2abfdc3a349 src/hotspot/share/runtime/arguments.cpp
--- a/src/hotspot/share/runtime/arguments.cpp   Tue Sep 18 13:44:15 2018 -0700
+++ b/src/hotspot/share/runtime/arguments.cpp   Tue Sep 18 15:12:59 2018 -0700
@@ -542,6 +542,7 @@
   { "CreateMinidumpOnCrash",        JDK_Version::jdk(9),  JDK_Version::undefined(), JDK_Version::undefined() },
   { "MustCallLoadClassInternal",    JDK_Version::jdk(10), JDK_Version::jdk(11), JDK_Version::jdk(12) },
   { "UnsyncloadClass",              JDK_Version::jdk(10), JDK_Version::jdk(11), JDK_Version::jdk(12) },
+  { "TLABStats",                    JDK_Version::jdk(12), JDK_Version::undefined(), JDK_Version::undefined() },

   // -------------- Obsolete Flags - sorted by expired_in --------------
   { "CheckAssertionStatusDirectives",JDK_Version::undefined(), JDK_Version::jdk(11), JDK_Version::jdk(12) },

The VMDeprecatedOptions.java test also needs to be updated:

diff -r e2abfdc3a349 test/hotspot/jtreg/runtime/CommandLine/VMDeprecatedOptions.java
--- a/test/hotspot/jtreg/runtime/CommandLine/VMDeprecatedOptions.java   Tue Sep 18 13:44:15 2018 -0700
+++ b/test/hotspot/jtreg/runtime/CommandLine/VMDeprecatedOptions.java   Tue Sep 18 15:18:14 2018 -0700
@@ -46,6 +46,7 @@
         {"InitialRAMFraction",        "64"},
         {"AssumeMP",                  "false"},
         {"UseMembar",                 "true"},
+        {"TLABStats",                 "false"},

         // deprecated alias flags (see also aliased_jvm_flags):
         {"DefaultMaxRAMFraction", "4"},