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8314100: G1: Improve collection set candidate selection code #15243

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tschatzl
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@tschatzl tschatzl commented Aug 11, 2023

Hi all,

discussions during review of JDK-8140326 indicated that he code surrounding selecting candidates after marking/rebuild for the collection set could be improved.

Testing: gha

Thanks,
Thomas


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  • JDK-8314100: G1: Improve collection set candidate selection code (Enhancement - P4)

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bridgekeeper bot commented Aug 11, 2023

👋 Welcome back tschatzl! 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 openjdk bot changed the title 8314100 8314100: G1: Improve collection set candidate selection code Aug 11, 2023
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openjdk bot commented Aug 11, 2023

@tschatzl 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.

@openjdk openjdk bot added the hotspot-gc hotspot-gc-dev@openjdk.org label Aug 11, 2023
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Passed tier1-3 too.

@tschatzl tschatzl marked this pull request as ready for review August 11, 2023 13:10
@openjdk openjdk bot added the rfr Pull request is ready for review label Aug 11, 2023
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mlbridge bot commented Aug 11, 2023

Webrevs

Comment on lines 154 to 161
bool should_add =
// We will skip any region that's currently used as an old GC
// alloc region (we should not consider those for collection
// before we fill them up). Otherwise the Old region must satisfy the liveness
// condition and have a complete remembered set.
!G1CollectedHeap::heap()->is_old_gc_alloc_region(r) &&
G1CollectionSetChooser::region_occupancy_low_enough_for_evac(r->live_bytes()) &&
r->rem_set()->is_complete();
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Does this work?

assert(!r->rem_set()->is_updating(), "inv");
if (!r->rem_set()->is_complete()) {
  return false;
}
if (G1CollectionSetChooser::region_occupancy_low_enough_for_evac(r->live_bytes())) {
  add_region(r);
} else {
  r->rem_set()->clear(true /* only_cardset */);
}

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I do not think so. Old GC alloc regions need special handling either way (unregistering them as such), and the suggested code may keep them as candidates - they may have a (complete) remembered set here (unless you suggest to change the meaning).

Not sure if breaking up the conjunction any further improves the code; the breakout of the earlier if (is_old() || !...) avoids the repetition for the remset clearing.

Something like

assert(!r->rem_set()->is_updating(), "must be");
if (!r->rem_set()->is_complete()) {
  return false;
}
bool should_add = !r->is_old_gc_alloc_region() || G1CollectionSetChooser::region_occupancy_low_enough_for_evac(r->live_bytes())
if (should_add) {
  add_region(r);
} else {
  r->rem_set()->clear(true /* only_cardset */);
}

would work if that is better for you.

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Yes, this looks better. The comment should make it clear whether is_old_gc_alloc_region is required for correctness or not. (I believe it is not.)

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openjdk bot commented Aug 18, 2023

@tschatzl 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:

8314100: G1: Improve collection set candidate selection code

Reviewed-by: ayang, iwalulya

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 122 new commits pushed to the master branch:

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.

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@openjdk openjdk bot added the ready Pull request is ready to be integrated label Aug 18, 2023
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Thanks @walulyai @albertnetymk for your reviews

/integrate

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openjdk bot commented Aug 21, 2023

Going to push as commit 8939d15.
Since your change was applied there have been 132 commits pushed to the master branch:

  • ec1f7a8: 8311630: [s390] Implementation of Foreign Function & Memory API (Preview)
  • c50315d: 8314495: Update to use jtreg 7.3.1
  • ed0f75f: 8313290: Misleading exception message from STS.Subtask::get when task forked after shutdown
  • febc34d: 8314610: hotspot can't compile with the latest of gtest because of
  • 58f5826: 8311222: strace004 can fail due to unexpected stack length after JDK-8309408
  • 395fc78: 8309475: Test java/foreign/TestByteBuffer.java fails: a problem with msync (aix)
  • f481477: 8314320: Mark runtime/CommandLine/ tests as flagless
  • fbe28ee: 8314481: JDWPTRANSPORT_ERROR_INTERNAL code in socketTransport.c can never be executed
  • 50a2ce0: 8310815: Clarify the name of the main class, services and provider classes in module descriptor
  • aecbb1b: 8314448: Coordinate DocLint and JavaDoc to report on unknown tags
  • ... and 122 more: https://git.openjdk.org/jdk/compare/52ec4bcb1bab15dbf0a9b2488d33a23cdc1cb0e1...master

Your commit was automatically rebased without conflicts.

@openjdk openjdk bot added the integrated Pull request has been integrated label Aug 21, 2023
@openjdk openjdk bot closed this Aug 21, 2023
@openjdk openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Aug 21, 2023
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openjdk bot commented Aug 21, 2023

@tschatzl Pushed as commit 8939d15.

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

@tschatzl tschatzl deleted the submit/8314100-improve-collection-set-candidate-selection branch August 23, 2023 12:30
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3 participants