8270347: ZGC: Adopt release-acquire ordering for forwarding table access #4763

weixlu · 2021-07-13T06:52:56Z

ZGC forwarding table records entries to track the destination of object relocation. Currently, the entry insertion (ZForwarding::insert()) adopts memory_order_conservative to guarantee that (1) the object copy always happens before the installation of forwardee, and (2) the other thread that accesses the same entry (ZForwarding::at() with load_acquire semantic) is able to access the correct contents of the forwarded object.

Let us consider memory_order_release for the entry insertion in ZForwarding::insert(). Pairing with the entry access in ZForwarding::at(), the forwarding table adopts release-acquire memory ordering. The two statements we mentioned above can also be guaranteed by the release-acquire ordering.

We performed an experiment on benchmark SPECjvm2008.sunflow on AArch64. The concurrent relocation time is listed below. The optimized version results in shorter average concurrent relocation time. Furthermore, it could benefit the throughput of ZGC.

$ grep "[50]00.*Phase: Concurrent Relocate" optimized.log
[500.506s][info][gc,stats    ]       Phase: Concurrent Relocate                           4.006 / 4.449         4.041 / 5.361         4.041 / 5.361         4.041 / 5.361       ms
[1000.506s][info][gc,stats    ]       Phase: Concurrent Relocate                           4.512 / 5.278         4.213 / 5.278         4.146 / 5.361         4.146 / 5.361       ms
[1500.506s][info][gc,stats    ]       Phase: Concurrent Relocate                           4.831 / 5.524         4.446 / 5.584         4.253 / 5.584         4.253 / 5.584       ms
[2000.506s][info][gc,stats    ]       Phase: Concurrent Relocate                           4.037 / 4.649         4.391 / 5.524         4.281 / 5.584         4.281 / 5.584       ms
[2500.506s][info][gc,stats    ]       Phase: Concurrent Relocate                           4.256 / 4.568         4.198 / 5.022         4.265 / 5.584         4.265 / 5.584       ms
[3000.506s][info][gc,stats    ]       Phase: Concurrent Relocate                           3.032 / 4.424         3.810 / 24.709        4.173 / 24.709        4.173 / 24.709      ms
[3500.506s][info][gc,stats    ]       Phase: Concurrent Relocate                           3.740 / 4.598         3.304 / 4.872         4.050 / 24.709        4.050 / 24.709      ms

$ grep "[50]00.*Phase: Concurrent Relocate" baseline.log
[500.545s][info][gc,stats    ]       Phase: Concurrent Relocate                           4.634 / 5.191         4.425 / 5.490         4.425 / 5.490         4.425 / 5.490       ms
[1000.545s][info][gc,stats    ]       Phase: Concurrent Relocate                           4.177 / 4.731         4.414 / 5.543         4.400 / 5.543         4.400 / 5.543       ms
[1500.545s][info][gc,stats    ]       Phase: Concurrent Relocate                           4.560 / 4.894         4.441 / 5.543         4.427 / 5.543         4.427 / 5.543       ms
[2000.546s][info][gc,stats    ]       Phase: Concurrent Relocate                           4.509 / 5.100         4.591 / 5.739         4.468 / 5.739         4.468 / 5.739       ms
[2500.545s][info][gc,stats    ]       Phase: Concurrent Relocate                           4.543 / 5.533         4.685 / 5.762         4.511 / 5.762         4.511 / 5.762       ms
[3000.546s][info][gc,stats    ]       Phase: Concurrent Relocate                           4.423 / 4.834         4.635 / 5.895         4.530 / 5.895         4.530 / 5.895       ms
[3500.545s][info][gc,stats    ]       Phase: Concurrent Relocate                           4.152 / 5.243         4.313 / 24.341        4.493 / 24.341        4.493 / 24.341      ms

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Issue

JDK-8270347: ZGC: Adopt release-acquire ordering for forwarding table access

Reviewers

Erik Österlund (@fisk - Reviewer)
Per Liden (@pliden - Reviewer)

Contributors

Hao Tang <albert.th@alibaba-inc.com>

Reviewing

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$ git fetch https://git.openjdk.java.net/jdk pull/4763/head:pull/4763
$ git checkout pull/4763

Update a local copy of the PR:
$ git checkout pull/4763
$ git pull https://git.openjdk.java.net/jdk pull/4763/head

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$ git pr checkout 4763

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$ git pr show -t 4763

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https://git.openjdk.java.net/jdk/pull/4763.diff

bridgekeeper · 2021-07-13T06:53:50Z

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openjdk · 2021-07-13T06:56:08Z

@weixlu 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.

weixlu · 2021-07-13T06:58:16Z

/covered

weixlu · 2021-07-13T06:59:12Z

/contributor add Hao Tang albert.th@alibaba-inc.com

openjdk · 2021-07-13T06:59:16Z

@weixlu
Contributor Hao Tang <albert.th@alibaba-inc.com> successfully added.

bridgekeeper · 2021-07-13T06:59:21Z

Thank you! Please allow for a few business days to verify that your employer has signed the OCA. Also, please note that pull requests that are pending an OCA check will not usually be evaluated, so your patience is appreciated!

tanghaoth90 · 2021-07-13T08:07:01Z

#4597 implements memory_order_release for AArch64. We think this could benefit ZGC as well.

mlbridge · 2021-07-15T12:04:22Z

Webrevs

00: Full (413560a2)

fisk

Looks good.

openjdk · 2021-07-16T08:45:01Z

⚠️ @weixlu the full name on your profile does not match the author name in this pull requests' HEAD commit. If this pull request gets integrated then the author name from this pull requests' HEAD commit will be used for the resulting commit. If you wish to push a new commit with a different author name, then please run the following commands in a local repository of your personal fork:

$ git checkout cas
$ git commit -c user.name='Preferred Full Name' --allow-empty -m 'Update full name'
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openjdk · 2021-07-16T08:45:03Z

@weixlu 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:

8270347: ZGC: Adopt release-acquire ordering for forwarding table access

Co-authored-by: Hao Tang <albert.th@alibaba-inc.com>
Reviewed-by: eosterlund, pliden

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 252 new commits pushed to the master branch:

c8add22: Merge
ada58d1: 8067223: [TESTBUG] Rename Whitebox API package
f8fb571: 8271150: Remove EA from JDK 17 version string starting with Initial RC promotion on Aug 5, 2021(B34)
84f0231: 8271419: Refactor test code for modifying CDS archive contents
0b95394: 8271624: Avoid unnecessary ThreadGroup.checkAccess calls when creating Threads
e621cff: 8271627: Use local field access in favor of Class.getClassLoader0
0a85236: 8193559: ugly DO_JAVA_THREADS macro should be replaced
db950ca: 8271348: Add stronger sanity check of thread state when polling for safepoint/handshakes
3e3051e: 8251329: (zipfs) Files.walkFileTree walks infinitely if zip has dir named "." inside
7a4c754: 8271611: Use SecurityConstants.ACCESS_PERMISSION in MethodHandles
... and 242 more: https://git.openjdk.java.net/jdk/compare/07e90524576f159fc16523430f1db62327c89a3b...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.

As you do not have Committer status in this project an existing Committer must agree to sponsor your change. Possible candidates are the reviewers of this PR (@fisk, @pliden) but any other Committer may sponsor as well.

➡️ To flag this PR as ready for integration with the above commit message, type /integrate in a new comment. (Afterwards, your sponsor types /sponsor in a new comment to perform the integration).

tanghaoth90 · 2021-07-19T02:52:31Z

Hi, it seems that a non-trivial patch requires at least two reviewers. @pliden would you please review this patch?

stooart-mon · 2021-07-19T09:57:13Z

I believe we're good because the release you've changed this to is matched by the ZForwarding::at() accesses the entries with an acquire, and I can find no other means of accessing entries.

stooart-mon

Looks good to me.

tanghaoth90 · 2021-07-20T07:14:07Z

Looks good to me.

@stooart-mon Thanks for reviewing. Could you please approve this pull request?

stooart-mon · 2021-07-20T09:53:19Z

I'm not a committer or reviewer, so I can't officially approve this.

pliden

Looks good!

pliden · 2021-08-03T09:24:42Z

I'll sponsor the change.

weixlu · 2021-08-03T11:26:04Z

@pliden @fisk @stooart-mon Thank you very much for your review.

weixlu · 2021-08-03T11:26:26Z

/integrate

openjdk · 2021-08-03T11:27:43Z

@weixlu
Your change (at version 413560a) is now ready to be sponsored by a Committer.

pliden · 2021-08-03T12:22:18Z

/sponsor

openjdk · 2021-08-03T12:23:26Z

Going to push as commit bdb50ca.
Since your change was applied there have been 253 commits pushed to the master branch:

b217a6c: 8271609: Misleading message for AbortVMOnVMOperationTimeoutDelay
c8add22: Merge
ada58d1: 8067223: [TESTBUG] Rename Whitebox API package
f8fb571: 8271150: Remove EA from JDK 17 version string starting with Initial RC promotion on Aug 5, 2021(B34)
84f0231: 8271419: Refactor test code for modifying CDS archive contents
0b95394: 8271624: Avoid unnecessary ThreadGroup.checkAccess calls when creating Threads
e621cff: 8271627: Use local field access in favor of Class.getClassLoader0
0a85236: 8193559: ugly DO_JAVA_THREADS macro should be replaced
db950ca: 8271348: Add stronger sanity check of thread state when polling for safepoint/handshakes
3e3051e: 8251329: (zipfs) Files.walkFileTree walks infinitely if zip has dir named "." inside
... and 243 more: https://git.openjdk.java.net/jdk/compare/07e90524576f159fc16523430f1db62327c89a3b...master

Your commit was automatically rebased without conflicts.

openjdk · 2021-08-03T12:23:40Z

@pliden @weixlu Pushed as commit bdb50ca.

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

8270347: ZGC: Adopt release-acquire ordering for forwarding table access

413560a

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weixlu mentioned this pull request Aug 9, 2021

8272138: ZGC: Adopt relaxed ordering for self-healing #5046

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8270347: ZGC: Adopt release-acquire ordering for forwarding table access #4763

8270347: ZGC: Adopt release-acquire ordering for forwarding table access #4763

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8270347: ZGC: Adopt release-acquire ordering for forwarding table access #4763

8270347: ZGC: Adopt release-acquire ordering for forwarding table access #4763

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