8278207: G1: Tighten verification in G1ResetSkipCompactingClosure #6698

albertnetymk · 2021-12-03T10:35:18Z

Simple change of expanding the verification logic to mirror its source.

Test: tier1-5

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Issue

JDK-8278207: G1: Tighten verification in G1ResetSkipCompactingClosure

Reviewers

Thomas Schatzl (@tschatzl - Reviewer)
Stefan Johansson (@kstefanj - Reviewer)

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Update a local copy of the PR:
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$ git pull https://git.openjdk.java.net/jdk pull/6698/head

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https://git.openjdk.java.net/jdk/pull/6698.diff

bridgekeeper · 2021-12-03T10:35:56Z

👋 Welcome back ayang! 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 · 2021-12-03T10:39:15Z

@albertnetymk 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 · 2021-12-03T10:42:36Z

Webrevs

01: Full - Incremental (f31805b1)
00: Full (3fcf2f5f)

kstefanj · 2021-12-06T14:42:58Z

src/hotspot/share/gc/g1/g1FullGCCompactTask.cpp

+#ifdef ASSERT
+    if (r->is_humongous()) {
+      oop obj = cast_to_oop(r->humongous_start_region()->bottom());
+      assert(_collector->mark_bitmap()->is_marked(obj), "must be live");
+    } else if (r->is_open_archive()) {
+      bool is_empty = (_collector->live_words(r->hrm_index()) == 0);
+      assert(!is_empty, "should contain at least one live obj");
+    } else if (r->is_closed_archive()) {
+      // nothing to assert
+    } else {
+      assert(_collector->live_words(region_index) > _collector->scope()->region_compaction_threshold(),
+             "should be quite full");
+    }
+#endif


What do you think about extracting this to a function. Something like:

void assert_should_reset(HeapRegion*) PRODUCT_RETURN;

But you might be able to come up with a better name :)

Considering this method is fairly short, I think having those asserts inlined doesn't hinder readability; instead, provides some documentation concerning in what context this method is invoked.

I think the fact that the method is short a good reason to extract the asserts, now the bulk of the method is asserts. If we want more documentation I would rather see a comment explaining in what situations regions might be marked as "skip compacting". We do have some documentation on this in G1FullGCHeapRegionAttr.

I'm fine with leaving the asserts here if you and others prefer it. One other question, can we ever end up here with a closed archive region? Those are marked SkipMarking so I guess they should be filtered out above?

If we want more documentation I would rather see a comment explaining in what situations regions might be marked as "skip compacting".

These asserts serve as "runnable" documentation -- less likely to deviate from the actual code.

One other question, can we ever end up here with a closed archive region? Those are marked SkipMarking so I guess they should be filtered out above?

Yes; you are right. I should put ShouldNotReachHere() for closed-archive regions.

tschatzl

I would probably also have preferred to move this lengthy assert into an extra method, but lgtm.

openjdk · 2021-12-13T09:42:50Z

@albertnetymk 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:

8278207: G1: Tighten verification in G1ResetSkipCompactingClosure

Reviewed-by: tschatzl, sjohanss

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 374 new commits pushed to the master branch:

2bbeae3: 8279668: x86: AVX2 versions of vpxor should be asserted
3121898: 8279703: G1: Remove unused force_not_compacted local in G1CalculatePointersClosure::do_heap_region
bf7bcaa: 8277748: Obsolete the MinInliningThreshold flag in JDK 19
126328c: 8279560: AArch64: generate_compare_long_string_same_encoding and LARGE_LOOP_PREFETCH alignment
ec5a455: 8279682: JFR: Remove dead code
6504458: 8279647: JFR: Unclosed directory stream
2f13872: 8279646: JFR: Remove recursive call in jdk.jfr.internal.Control
2f7665b: 8279644: hsdis may not work when it was built with --with-binutils=system
4471e95: 8279645: JFR: The cacheEventType in Dispatcher is never assigned
d7e6e9b: 8279643: JFR: Explain why path is sometimes missing from FileRead and FileWrite events
... and 364 more: https://git.openjdk.java.net/jdk/compare/53df9ffbca841358eb8bb49837ec4bf43a1a743b...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.

bridgekeeper · 2022-01-10T14:28:45Z

@albertnetymk This pull request has been inactive for more than 4 weeks and will be automatically closed if another 4 weeks passes without any activity. To avoid this, simply add a new comment to the pull request. Feel free to ask for assistance if you need help with progressing this pull request towards integration!

kstefanj

I'm ok with leaving this as is as well.

albertnetymk · 2022-01-11T14:03:48Z

Thanks for the review.

/integrate

openjdk · 2022-01-11T14:05:09Z

Going to push as commit 08e14c6.
Since your change was applied there have been 377 commits pushed to the master branch:

c08b2ac: 8225093: Special property jdk.boot.class.path.append should not default to empty string
4c52eb3: 8279669: test/jdk/com/sun/jdi/TestScaffold.java uses wrong condition
d46410c: 8279785: JFR: 'jfr configure' should show default values
2bbeae3: 8279668: x86: AVX2 versions of vpxor should be asserted
3121898: 8279703: G1: Remove unused force_not_compacted local in G1CalculatePointersClosure::do_heap_region
bf7bcaa: 8277748: Obsolete the MinInliningThreshold flag in JDK 19
126328c: 8279560: AArch64: generate_compare_long_string_same_encoding and LARGE_LOOP_PREFETCH alignment
ec5a455: 8279682: JFR: Remove dead code
6504458: 8279647: JFR: Unclosed directory stream
2f13872: 8279646: JFR: Remove recursive call in jdk.jfr.internal.Control
... and 367 more: https://git.openjdk.java.net/jdk/compare/53df9ffbca841358eb8bb49837ec4bf43a1a743b...master

Your commit was automatically rebased without conflicts.

openjdk · 2022-01-11T14:05:32Z

@albertnetymk Pushed as commit 08e14c6.

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

full-gc-compact-assert

3fcf2f5

openjdk bot added the rfr label Dec 3, 2021

openjdk bot added the hotspot-gc label Dec 3, 2021

kstefanj reviewed Dec 6, 2021

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closed archive

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tschatzl approved these changes Dec 13, 2021

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kstefanj approved these changes Jan 11, 2022

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openjdk bot closed this Jan 11, 2022

openjdk bot removed ready rfr labels Jan 11, 2022

albertnetymk deleted the full-gc-compact-assert branch Jan 11, 2022

openjdk / jdk Public

8278207: G1: Tighten verification in G1ResetSkipCompactingClosure #6698

8278207: G1: Tighten verification in G1ResetSkipCompactingClosure #6698

albertnetymk commented Dec 3, 2021 •

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openjdk / jdk Public

8278207: G1: Tighten verification in G1ResetSkipCompactingClosure #6698

8278207: G1: Tighten verification in G1ResetSkipCompactingClosure #6698

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albertnetymk commented Dec 3, 2021 • edited by openjdk[bot] bot

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