8303244: G1: call CardTable::clear_MemRegion directly

[albertnetymk]

Simple refactoring to skip a guard in card-table clearing.

Test: hotspot_gc

---

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Issue

• JDK-8303244: G1: call CardTable::clear_MemRegion directly

Reviewers

• Y. Srinivas Ramakrishna (@ysramakrishna - Reviewer)
• Kim Barrett (@kimbarrett - Reviewer)

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[openjdk]

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[mlbridge]

Webrevs

• 00: Full (33a443a2)

[openjdk]

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

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8303244: G1: call CardTable::clear_MemRegion directly

Reviewed-by: ysr, kbarrett

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At the time when this comment was updated there had been 91 new commits pushed to the master branch:

• 5b2e2e4: 8302590: Add String.indexOf(int ch, int fromIndex, int toIndex)
• cd4b88d: 8292269: Replace FileMapInfo::fail_continue() with Unified Logging
• ae29054: 8303175: (fs) Deprecate com.sun.nio.file.SensitivityWatchEventModifier for removal
• a04b104: 8303413: (fs) Ignore polling interval sensitivity modifiers in PollingWatchService
• 9944314: 8303587: Remove VMOutOfMemoryError001 test from the problem list after 8303198
• a50dc67: 8303527: update for deprecated sprintf for jdk.hotspot.agent
• 40c5edf: 8303181: Memory leak in ClassLoaderExt::setup_app_search_path
• 29ee7c3: 8303523: Cleanup problem listing of nsk/jvmti/AttachOnDemand/attach002a/TestDescription.java
• e3016c1: 8303472: Display name for region TR
• ae797c6: 8301117: Remove old_size param from ResizeableResourceHashtable::resize()
• ... and 81 more: https://git.openjdk.org/jdk/compare/a43931b79cb25d218e8f9b4d4f3a106f59cb2d37...master

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[kimbarrett]

I think the code changes are okay.

But while looking at it I wondered what the difference between CT::clear and
CT::clear_MemRegion might be. The former has no description. The latter has a
description that seems wrong.

I also wonder why dirty_MemRegion uses an explicit loop over the cards while
clear_MemRegion uses memset. It seems like that difference has been there
since before the mercurial age.

[albertnetymk]

what the difference between CT::clear and CT::clear_MemRegion might be.

The former guards against memregions not covered by _covered. (Maybe or maybe not really needed for Serial/Parallel; will take a look after this PR.)

dirty_MemRegion vs clear_MemRegion

Maybe there's no need for such discrepancy. Can be fixed in another PR.

[kimbarrett]

what the difference between CT::clear and CT::clear_MemRegion might be.

The former guards against memregions not covered by _covered. (Maybe or maybe not really needed for Serial/Parallel; will take a look after this PR.)

Right, but that's not what the description comments for the xxx_MemRegion functions say.

dirty_MemRegion vs clear_MemRegion

Maybe there's no need for such discrepancy. Can be fixed in another PR.

That would be fine.

[albertnetymk]

(not all of which must be covered.) for clear_MemRegion is inaccurate. I will fix that in another PR.

[kimbarrett]

Looks good.

[albertnetymk]

Thanks for the review.

/integrate

[openjdk]

Going to push as commit ec4e8aa.
Since your change was applied there have been 102 commits pushed to the master branch:

• 5753ab5: 8297454: javax/swing/JComponent/7154030/bug7154030.java failed with "Exception: Failed to show opaque button"
• fa1cebe: 8303266: Prefer ArrayList to LinkedList in JImageTask
• 5f153e0: 8302780: Add support for vectorized arraycopy GC barriers
• d00a767: 8295737: macOS: Print content cut off when width > height with portrait orientation
• 15c76e4: 8301254: UNIX sun/font coding does not detect SuSE in openSUSE Leap distribution
• 3eff1a0: 8303630: Move nsk/jvmti/AttachOnDemand/attach002a/TestDescription.java back to general problem list
• 10d6a8e: 8299518: HotSpotVirtualMachine shared code across different platforms
• 148900c: 8303562: Remove obsolete comments in os::pd_attempt_reserve_memory_at
• 1bb39a9: 8302027: Port fdlibm trig functions (sin, cos, tan) to Java
• 9fdbf3c: 8303588: [JVMCI] make JVMCI source directories conform with standard layout
• ... and 92 more: https://git.openjdk.org/jdk/compare/a43931b79cb25d218e8f9b4d4f3a106f59cb2d37...master

Your commit was automatically rebased without conflicts.

[openjdk]

@albertnetymk Pushed as commit ec4e8aa.

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