RFR: 8204210: Implementation: JEP 333: ZGC: A Scalable Low-Latency Garbage Collector (Experimental)

[Rickard Bäckman]

Hi,

I've looked at the C2 parts of things with Nils by my side. 
There are a couple of small things to note. 

classes.cpp misses an undef for optionalmacro.

compile.cpp the print_method should probably be within the {} of
macroExpand.

escape.cpp has two else if cases where the code looks very common.
Please make this into a function if possible?

opcodes.cpp misses an undef for optionalmacro.

In C2 in general, maybe BarrierSet::barrier_set()->barrier_set_c2()
coule be Compile::barrier_set()?

Looks good, great work everyone!

/R

On 06/01, Per Liden wrote:
> Hi,
> 
> Please review the implementation of JEP 333: ZGC: A Scalable Low-Latency
> Garbage Collector (Experimental)
> 
> Please see the JEP for more information about the project. The JEP is
> currently in state "Proposed to Target" for JDK 11.
> 
> https://bugs.openjdk.java.net/browse/JDK-8197831
> 
> Additional information in can also be found on the ZGC project wiki.
> 
> https://wiki.openjdk.java.net/display/zgc/Main
> 
> 
> Webrevs
> -------
> 
> To make this easier to review, we've divided the change into two webrevs.
> 
> * ZGC Master: http://cr.openjdk.java.net/~pliden/8204210/webrev.0-master
> 
>   This patch contains the actual ZGC implementation, the new unit tests and
> other changes needed in HotSpot.
> 
> * ZGC Testing: http://cr.openjdk.java.net/~pliden/8204210/webrev.0-testing
> 
>   This patch contains changes to existing tests needed by ZGC.
> 
> 
> Overview of Changes
> -------------------
> 
> Below follows a list of the files we add/modify in the master patch, with a
> short summary describing each group.
> 
> * Build support - Making ZGC an optional feature.
> 
>   make/autoconf/hotspot.m4
>   make/hotspot/lib/JvmFeatures.gmk
>   src/hotspot/share/utilities/macros.hpp
> 
> * C2 AD file - Additions needed to generate ZGC load barriers (adlc does not
> currently offer a way to easily break this out).
> 
>   src/hotspot/cpu/x86/x86.ad
>   src/hotspot/cpu/x86/x86_64.ad
> 
> * C2 - Things that can't be easily abstracted out into ZGC specific code,
> most of which is guarded behind a #if INCLUDE_ZGC and/or if (UseZGC)
> condition. There should only be two logic changes (one in idealKit.cpp and
> one in node.cpp) that are still active when ZGC is disabled. We believe
> these are low risk changes and should not introduce any real change i
> behavior when using other GCs.
> 
>   src/hotspot/share/adlc/formssel.cpp
>   src/hotspot/share/opto/*
>   src/hotspot/share/compiler/compilerDirectives.hpp
> 
> * General GC+Runtime - Registering ZGC as a collector.
> 
>   src/hotspot/share/gc/shared/*
>   src/hotspot/share/runtime/vmStructs.cpp
>   src/hotspot/share/runtime/vm_operations.hpp
>   src/hotspot/share/prims/whitebox.cpp
> 
> * GC thread local data - Increasing the size of data area by 32 bytes.
> 
>   src/hotspot/share/gc/shared/gcThreadLocalData.hpp
> 
> * ZGC - The collector itself.
> 
>   src/hotspot/share/gc/z/*
>   src/hotspot/cpu/x86/gc/z/*
>   src/hotspot/os_cpu/linux_x86/gc/z/*
>   test/hotspot/gtest/gc/z/*
> 
> * JFR - Adding new event types.
> 
>   src/hotspot/share/jfr/*
>   src/jdk.jfr/share/conf/jfr/*
> 
> * Logging - Adding new log tags.
> 
>   src/hotspot/share/logging/*
> 
> * Metaspace - Adding a friend declaration.
> 
>   src/hotspot/share/memory/metaspace.hpp
> 
> * InstanceRefKlass - Adjustments for concurrent reference processing.
> 
>   src/hotspot/share/oops/instanceRefKlass.inline.hpp
> 
> * vmSymbol - Disabled clone intrinsic for ZGC.
> 
>   src/hotspot/share/classfile/vmSymbols.cpp
> 
> * Oop Verification - In four cases we disabled oop verification because it
> do not makes sense or is not applicable to a GC using load barriers.
> 
>   src/hotspot/cpu/x86/c1_LIRAssembler_x86.cpp
>   src/hotspot/cpu/x86/stubGenerator_x86_64.cpp
>   src/hotspot/share/compiler/oopMap.cpp
>   src/hotspot/share/runtime/jniHandles.cpp
> 
> * StackValue - Apply a load barrier in case of OSR. This is a bit of a hack.
> However, this will go away in the future, when we have the next iteration of
> C2's load barriers in place (aka "C2 late barrier insertion").
> 
>   src/hotspot/share/runtime/stackValue.cpp
> 
> * JVMTI - Adding an assert() to catch problems if the tagmap hashing is
> changed in the future.
> 
>   src/hotspot/share/prims/jvmtiTagMap.cpp
> 
> * Legal - Adding copyright/license for 3rd party hash function used in
> ZHash.
> 
>   src/java.base/share/legal/c-libutl.md
> 
> * SA - Adding basic ZGC support.
> 
>   src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/*
> 
> 
> Testing
> -------
> 
> * Unit testing
> 
>   A number of new ZGC specific gtests have been added, in
> test/hotspot/gtest/gc/z/
> 
> * Regression testing
> 
>   No new failures in Mach5, with ZGC enabled, tier{1,2,3,4,5,6}
>   No new failures in Mach5, with ZGC disabled, tier{1,2,3}
> 
> * Stress testing
> 
>   We have been continuously been running a number stress tests throughout
> the development, these include:
> 
>     specjbb2000
>     specjbb2005
>     specjbb2015
>     specjvm98
>     specjvm2008
>     dacapo2009
>     test/hotspot/jtreg/gc/stress/gcold
>     test/hotspot/jtreg/gc/stress/systemgc
>     test/hotspot/jtreg/gc/stress/gclocker
>     test/hotspot/jtreg/gc/stress/gcbasher
>     test/hotspot/jtreg/gc/stress/finalizer
>     Kitchensink
> 
> 
> Thanks!
> 
> /Per, Stefan & the ZGC team