RFR (round 1), JDK-8214259: Implementation: JEP 189: Shenandoah: A Low-Pause Garbage Collector

Vladimir Kozlov vladimir.kozlov at oracle.com
Mon Nov 26 23:12:46 UTC 2018


Hi Roman,

You need to check if shenandoahgc is disabled first - check DISABLED_JVM_FEATURES list (see code for jvmci).

Do you support 32-bit x86? You have OPENJDK_TARGET_CPU == xx86 check.

Do you support all x86 OSs?

Why you set VM CFLAGS when shenandoahgc is not enabled? It is in JvmFeatures.gmk.

I looked on C2 changes. It has INCLUDE_SHENANDOAHGC, checks and new gc specific nodes. This looks intrusive. I hope you 
clean it up.

Thanks,
Vladimir

On 11/26/18 2:47 PM, Erik Joelsson wrote:
> Build changes look ok to me.
> 
> /Erik
> 
> On 2018-11-26 13:39, Roman Kennke wrote:
>> Hi,
>>
>> This is the first round of changes for including Shenandoah GC into
>> mainline.
>> I divided the review into parts that roughly correspond to the mailing lists
>> that would normally review it, and I divided it into 'shared' code
>> changes and
>> 'shenandoah' code changes (actually, mostly additions). The intend is to
>> eventually
>> push them as single 'combined' changeset, once reviewed.
>>
>> JEP:
>>    https://openjdk.java.net/jeps/189
>> Bug entry:
>>
>>   https://bugs.openjdk.java.net/browse/JDK-8214259
>>
>> Webrevs:
>>    http://cr.openjdk.java.net/~rkennke/shenandoah-upstream/00/
>>
>> For those who want to see the full change, have a look at the
>> shenandoah-complete
>> <http://cr.openjdk.java.net/~rkennke/shenandoah-upstream/00/shenandoah-complete/>
>> directory,
>> it contains the full combined webrev. Alternatively, there is the file
>> shenandoah-master.patch
>> <http://cr.openjdk.java.net/~rkennke/shenandoah-upstream/00/shenandoah-master.patch>,
>> which is what I intend to commit (and which should be equivalent to the
>> 'shenandoah-complete' webrev).
>>
>> Sections to review (at this point) are the following:
>>   *) shenandoah-gc
>> <http://cr.openjdk.java.net/~rkennke/shenandoah-upstream/00/shenandoah-gc/>
>>      - Actual Shenandoah implementation, almost completely residing in
>> gc/shenandoah
>>
>>   *) shared-gc
>> <http://cr.openjdk.java.net/~rkennke/shenandoah-upstream/00/shared-gc/>
>>      - This is mostly boilerplate that is common to any GC
>>      - referenceProcessor.cpp has a little change to make one assert not
>> fail (next to CMS and G1)
>>      - taskqueue.hpp has some small adjustments to enable subclassing
>>
>>   *) shared-serviceability
>> <http://cr.openjdk.java.net/~rkennke/shenandoah-upstream/00/shared-serviceability/>
>>      - The usual code to support another GC
>>
>>   *) shared-runtime
>> <http://cr.openjdk.java.net/~rkennke/shenandoah-upstream/00/shared-runtime/>
>>      - A number of friends declarations to allow Shenandoah iterators to
>> hook up with,
>>        e.g. ClassLoaderData, CodeCache, etc
>>      - Warning and disabling JFR LeakProfiler
>>      - fieldDescriptor.hpp added is_stable() accessor, for use in
>> Shenandoah C2 optimizations
>>      - Locks initialization in mutexLocker.cpp as usual
>>      - VM operations defines for Shenandoah's VM ops
>>      - globalDefinitions.hpp added UINT64_FORMAT_HEX_W for use in
>> Shenandoah's logging
>>      - The usual macros in macro.hpp
>>
>>   *) shared-build
>> <http://cr.openjdk.java.net/~rkennke/shenandoah-upstream/00/shared-build/>
>>      - Add shenandoah feature, enabled by default, as agreed with
>> Vladimir K. beforehand
>>      - Some flags for shenandoah-enabled compilation to get
>> SUPPORT_BARRIER_ON_PRIMITIVES
>>        and SUPPORT_NOT_TO_SPACE_INVARIANT which is required for
>> Shenandoah's barriers
>>      - --param inline-unit-growth=1000 settings for 2 shenandoah source
>> files, which is
>>        useful to get the whole marking loop inlined (observed significant
>> regression if we
>>        don't)
>>
>>   *) shared-tests
>> <http://cr.openjdk.java.net/~rkennke/shenandoah-upstream/00/shared-tests/>
>>      - Test infrastructure to support Shenandoah
>>      - Shenandoah test groups
>>      - Exclude Shenandoah in various tests that can be run with selected GC
>>      - Enable/add configure for Shenandoah for tests that make sense to
>> run with it
>>
>>   *) shenandoah-tests
>> <http://cr.openjdk.java.net/~rkennke/shenandoah-upstream/00/shenandoah-tests/>
>>      - Shenandoah specific tests, most reside in gc/shenandoah subdirectory
>>      - A couple of tests configurations have been added, e.g.
>> TestGCBasherWithShenandoah.java
>>
>> I intentionally left out shared-compiler for now, because we have some
>> work left to do
>> there, but if you click around you'll find the patch anyway, in case you
>> want to take
>> a peek at it.
>>
>> We have regular builds on:
>>    - {Linux} x {x86_64, x86_32, armhf, aarch64, ppc64el, s390x}
>>    - {Windows} x {x86_64},
>>    - {MacOS X} x {x86_64}
>>
>> This also routinely passes:
>>    - the new Shenandoah tests
>>    - jcstress with/without aggressive Shenandoah verification
>>    - specjvm2008 with/without aggressive Shenandoah verification
>>
>>
>> I'd like to thank my collegues at Red Hat: Christine Flood, she deserves
>> the credit for being the original inventor of Shenandoah, Aleksey
>> Shiplëv, Roland Westrelin & Zhengyu Gu for their countless
>> contributions, everybody else in Red Hat's OpenJDK team for testing,
>> advice and support, my collegues in Oracle's GC, runtime and compiler
>> teams for tirelessly helping with and reviewing all the GC interface and
>> related changes, and of course the many early adopters for reporting
>> bugs and success stories and feature requests: we wouldn't be here
>> without any of you!
>>
>> Best regards,
>> Roman
>>


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