Summary

The HotSpot option -XX:+FastTLABRefill should be deprecated and set to a default of off.

Problem

• Newly integrated Memory-Leak Profiler doesn't work with FastTLABRefill
• Upcoming Low Overhead profiler doesn't work with FastTLABRefill
• Option complicates already complicated code paths
• Option is actually default off (if you do not change default GC from G1)
• Only works with C1 (interpreter and C2 don't use this option)
• Only works with SerialGC and ParallelGC (and CMS)

Note: When using Serial/Parallel and only C1 there is a performances regression of 1%.

Solution

The option should be removed and this first step is to deprecate it and set it to false.

Specification

    diff -r 9a9c764bc2d5 src/hotspot/share/runtime/arguments.cpp
    --- a/src/hotspot/share/runtime/arguments.cpp   Mon Nov 06 10:20:01 2017 +0100
    +++ b/src/hotspot/share/runtime/arguments.cpp   Wed Nov 08 09:58:24 2017 +0100
    @@ -386,2 +386,3 @@
       { "IgnoreUnverifiableClassesDuringDump", JDK_Version::jdk(10),  JDK_Version::undefined(), JDK_Version::undefined() },
    +  { "FastTLABRefill",                      JDK_Version::jdk(10), JDK_Version::jdk(11), JDK_Version::jdk(12) },

    diff -r 9a9c764bc2d5 src/hotspot/share/runtime/globals.hpp
    --- a/src/hotspot/share/runtime/globals.hpp Mon Nov 06 10:20:01 2017 +0100
    +++ b/src/hotspot/share/runtime/globals.hpp Wed Nov 08 09:58:24 2017 +0100
    @@ -2022,3 +2022,3 @@
                                                                                 \
    -  product(bool, FastTLABRefill, true,                                       \
    +  product(bool, FastTLABRefill, false,                                      \
    !           "(Deprecated) Use fast TLAB refill code")                        \