8236176: Parallel GC SplitInfo comment should be updated for shadow regions #5195

walulyai · 2021-08-20T06:48:18Z

Hi all,

Please review this small change to add a high-level description of how shadow regions are utilized during the compact phase of the parallel GC. There is no special handling of Splitinfo by the shadow regions; the destination computation and the handling of partial_objects are done during the summary phase while the shadow regions optimization only applies to compaction.

Additionally, some unused variables are cleaned up.

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Change must be properly reviewed

Issue

JDK-8236176: Parallel GC SplitInfo comment should be updated for shadow regions

Reviewers

Thomas Schatzl (@tschatzl - Reviewer) ⚠️ Review applies to 52fbb6f
Albert Mingkun Yang (@albertnetymk - Reviewer)

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$ git checkout pull/5195

Update a local copy of the PR:
$ git checkout pull/5195
$ git pull https://git.openjdk.java.net/jdk pull/5195/head

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$ git pr checkout 5195

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https://git.openjdk.java.net/jdk/pull/5195.diff

…egions

bridgekeeper · 2021-08-20T06:48:46Z

👋 Welcome back iwalulya! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2021-08-20T06:51:11Z

@walulyai The following label will be automatically applied to this pull request:

hotspot-gc

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

mlbridge · 2021-08-20T06:55:37Z

Webrevs

01: Full - Incremental (b394ba83)
00: Full (52fbb6fa)

tschatzl · 2021-08-23T11:07:26Z

src/hotspot/share/gc/parallel/psParallelCompact.hpp

+// During compaction, there is a natural task dependency among regions because
+// destination regions may also be source regions themselves.  Consequently, the
+// destination regions are not available for processing until all live objects
+// within them are evacuated to their destinations. These dependencies lead to


There is a mix of one and two spaces after a full stop (5 times I think) in this and the next paragraph. I recommend using two spaces like in the above paragraphs for uniformity.

tschatzl · 2021-08-23T11:13:22Z

src/hotspot/share/gc/parallel/psParallelCompact.hpp

@@ -961,6 +961,25 @@ inline void ParMarkBitMapClosure::decrement_words_remaining(size_t words) {
 // regions and regions compacting into themselves.  There is always at least 1
 // region that can be put on the ready list.  The regions are atomically added
 // and removed from the ready list.
+//


This commentactually refers to the sentence: "// An alternate strategy is being investigated for this deferral of updating." above.

This sentence should be removed as this offers no information about the current algorithm. Fwiw I do not know that actually anyone is working on that, and if so, a CR in JIRA would be more appropriate. I could not find anything in JIRA about work on this, and given that comment is pretty old, this is just confusing.

tschatzl

Lgtm apart from my comments about some comment typos.

openjdk · 2021-08-23T11:15:34Z

@walulyai This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8236176: Parallel GC SplitInfo comment should be updated for shadow regions

Reviewed-by: tschatzl, ayang

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 49 new commits pushed to the master branch:

c5a2712: 8272850: Drop zapping values in the Zap* option descriptions
1e3e333: 8272884: Make VoidClosure::do_void pure virtual
0f428ca: 8272570: C2: crash in PhaseCFG::global_code_motion
b17b821: 8272639: jpackaged applications using microphone on mac
0e7288f: 8267125: AES Galois CounterMode (GCM) interleaved implementation using AVX512 + VAES instructions
6ace805: 8272856: DoubleFlagWithIntegerValue uses G1GC-only flag
c547ead: 8272916: Copyright year was modified unintentionally in jlink.properties and ImagePluginStack.java
aaedac6: 8265261: java/nio/file/Files/InterruptCopy.java fails with java.lang.RuntimeException: Copy was not interrupted
d34f17c: 8270195: Add missing links between methods of JavaFX properties
f608e81: 8264322: Generate CDS archive when creating custom JDK image
... and 39 more: https://git.openjdk.java.net/jdk/compare/03b5e99d998e037f84e9e2395b49321979c0acd8...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

walulyai · 2021-08-25T10:17:49Z

Thanks for the reviews!

/integrate

openjdk · 2021-08-25T10:19:06Z

Going to push as commit 63e062f.
Since your change was applied there have been 49 commits pushed to the master branch:

c5a2712: 8272850: Drop zapping values in the Zap* option descriptions
1e3e333: 8272884: Make VoidClosure::do_void pure virtual
0f428ca: 8272570: C2: crash in PhaseCFG::global_code_motion
b17b821: 8272639: jpackaged applications using microphone on mac
0e7288f: 8267125: AES Galois CounterMode (GCM) interleaved implementation using AVX512 + VAES instructions
6ace805: 8272856: DoubleFlagWithIntegerValue uses G1GC-only flag
c547ead: 8272916: Copyright year was modified unintentionally in jlink.properties and ImagePluginStack.java
aaedac6: 8265261: java/nio/file/Files/InterruptCopy.java fails with java.lang.RuntimeException: Copy was not interrupted
d34f17c: 8270195: Add missing links between methods of JavaFX properties
f608e81: 8264322: Generate CDS archive when creating custom JDK image
... and 39 more: https://git.openjdk.java.net/jdk/compare/03b5e99d998e037f84e9e2395b49321979c0acd8...master

Your commit was automatically rebased without conflicts.

openjdk · 2021-08-25T10:19:21Z

@walulyai Pushed as commit 63e062f.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

walulyai added 4 commits August 18, 2021 16:59

8236176: Parallel GC SplitInfo comment should be updated for shadow r…

c9e1d1c

…egions

Merge branch 'master' into JDK-8236176_Paralle_SplitInfo_shadow_regions

fb7c4c8

minor type

e58aa83

cleanup

52fbb6f

openjdk bot added the rfr Pull request is ready for review label Aug 20, 2021

openjdk bot added the hotspot-gc hotspot-gc-dev@openjdk.org label Aug 20, 2021

tschatzl reviewed Aug 23, 2021

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tschatzl approved these changes Aug 23, 2021

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openjdk bot added the ready Pull request is ready to be integrated label Aug 23, 2021

Thomas review

b394ba8

albertnetymk approved these changes Aug 25, 2021

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openjdk bot closed this Aug 25, 2021

openjdk bot added integrated Pull request has been integrated and removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Aug 25, 2021

8236176: Parallel GC SplitInfo comment should be updated for shadow regions #5195

8236176: Parallel GC SplitInfo comment should be updated for shadow regions #5195

walulyai commented Aug 20, 2021 •

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openjdk bot commented Aug 25, 2021

8236176: Parallel GC SplitInfo comment should be updated for shadow regions #5195

8236176: Parallel GC SplitInfo comment should be updated for shadow regions #5195

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walulyai commented Aug 20, 2021 • edited by openjdk bot

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