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

Roman Kennke rkennke at redhat.com
Mon Nov 26 21:39:30 UTC 2018


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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