8329655: Cleanup KlassObj and klassOop names after the PermGen removal #18618

stefank · 2024-04-04T09:45:58Z

We have a few places that uses the terms KlassObj and klassOop when referring to Klasses. This is old code from before the PermGen removal, when Klasses also were Java objects.

These names tripped me up when I was reading the heap heapInspection.cpp and first though we were mixing the klass mirror objects and klass pointers in the hash code calculation:

   // An aligned reference address (typically the least
   // address in the perm gen) used for hashing klass
   // objects.
   HeapWord* _ref;
...
_ref = (HeapWord*) Universe::boolArrayKlassObj();
...
uint KlassInfoTable::hash(const Klass* p) {
  return (uint)(((uintptr_t)p - (uintptr_t)_ref) >> 2);
}

I propose that we rename these functions (and stop casting the Klass* to a (HeapWord*)).

Tested with serviceability/dcmd/gc/ClassHistogramTest.java but will run this through our lower tiers.

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JDK-8329655: Cleanup KlassObj and klassOop names after the PermGen removal (Enhancement - P4)

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Roman Kennke (@rkennke - Reviewer)
Coleen Phillimore (@coleenp - Reviewer)

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bridgekeeper · 2024-04-04T09:46:49Z

👋 Welcome back stefank! 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 · 2024-04-04T09:47:11Z

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

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

8329655: Cleanup KlassObj and klassOop names after the PermGen removal

Reviewed-by: rkennke, coleenp

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At the time when this comment was updated there had been 3 new commits pushed to the master branch:

21867c9: 8313332: Simplify lazy jmethodID cache in InstanceKlass
b9da140: 8329594: G1: Consistent Titles to Thread Work Items.
a169c06: 8329580: Parallel: Remove VerifyObjectStartArray

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openjdk · 2024-04-04T09:47:34Z

@stefank The following labels will be automatically applied to this pull request:

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hotspot
serviceability

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

mlbridge · 2024-04-04T09:51:16Z

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01: Full - Incremental (85f6bbe6)
00: Full (02bcbd89)

rkennke

This is a useful change, it has tripped me up a couple of times, too. Change mostly looks good, just a few minor suggestions.

rkennke · 2024-04-04T09:55:38Z

src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp


  ldrw(scan_temp, Address(recv_klass, Klass::vtable_length_offset()));

-  // %%% Could store the aligned, prescaled offset in the klassoop.


Unrelated, but what's the point of the %%% in all those comments? Might want to remove that, while you're there.

I think it is an old-style TODO. I'm considering if we shouldn't just remove these comments. What do people think about that?

I'm not even sure what they want to say, really. Should be good to remove, and if anybody can make sense of it, record an issue in the bug-tracker?

OK. I removed the %%%. I'll wait a little bit to see if someone else wants to keep them for some reason, if not, I'll remove them.

I think leaving these comments without the %%% seems fine. Describing this idea in a CR is a lot more difficult than seeing it in context as commentary, and unless the enhancement has other motivation, it won't be picked up. Leaving the comment as a clue seems useful.

rkennke · 2024-04-04T10:07:11Z

src/hotspot/share/memory/heapInspection.cpp

 KlassInfoTable::KlassInfoTable(bool add_all_classes) {
  _size_of_instances_in_words = 0;
-  _ref = (HeapWord*) Universe::boolArrayKlassObj();
+  _ref = (uintptr_t) Universe::boolArrayKlass();


It seems weird (non-obvious) to cast to uintptr_t here. I see it is only used in KlassInfoTable::hash(), which is weird, too. I am not sure that this even does a useful hashing. Might be worth to get rid of the whole thing and use the fastHash stuff that @rose00 proposed for Lilliput. Perhaps in a follow-up. I'd probably either cast to void* or Klass*, or cast to uintptr_t as you did and remove the unnecessary cast in ::hash().

I agree. I'll start by removing the redundant cast in ::hash().

rkennke

Thanks! Looks good to me, now.

Roman

coleenp

This is good. The Obj was confusing.

coleenp · 2024-04-04T13:25:23Z

src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp


  ldrw(scan_temp, Address(recv_klass, Klass::vtable_length_offset()));

-  // %%% Could store the aligned, prescaled offset in the klassoop.


I think leaving these comments without the %%% seems fine. Describing this idea in a CR is a lot more difficult than seeing it in context as commentary, and unless the enhancement has other motivation, it won't be picked up. Leaving the comment as a clue seems useful.

coleenp · 2024-04-04T13:27:55Z

src/hotspot/share/memory/heapInspection.hpp

  size_t _size_of_instances_in_words;

  // An aligned reference address (typically the least
-  // address in the perm gen) used for hashing klass


Rats I missed this.

stefank · 2024-04-05T07:39:24Z

Thanks for the reviews!
/integrate

openjdk · 2024-04-05T07:39:50Z

Going to push as commit 71d48bc.
Since your change was applied there have been 21 commits pushed to the master branch:

b71acc7: 8329089: Empty immutable list throws the wrong exception type for remove(first | last) operations
1131bb7: 8329261: G1: interpreter post-barrier x86 code asserts index size of wrong buffer
6bc6392: 8329201: C2: Replace TypeInterfaces::intersection_with() + eq() with contains()
9da5170: 8327978: C2 SuperWord: Fix compilation time regression in dependency graph traversal after JDK-8325651
c1cfb43: 8329109: Threads::print_on() tries to print CPU time for terminated GC threads
5860a48: 8329624: Add visitors for preview language features
0b01144: 8329720: Gtest failure printing markword after JDK-8325303
34f7974: 8325303: Replace markWord.is_neutral() with markWord.is_unlocked()
27cfcef: 8329651: TestLibGraal.java crashes with assert(_stack_base != nullptr)
e1183ac: 8329703: Remove unused apple.jpeg file from SwingSet2 demo
... and 11 more: https://git.openjdk.org/jdk/compare/8efd7aa6c1671fa7d40c5c43bed140a493cfcf72...master

Your commit was automatically rebased without conflicts.

openjdk · 2024-04-05T07:39:56Z

@stefank Pushed as commit 71d48bc.

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

8329655: Cleanup KlassObj and klassOop names after the PermGen removal

02bcbd8

openjdk bot changed the title ~~8329655: Cleanup KlassObj and klassOop names after the PermGen removal~~ 8329655: Cleanup KlassObj and klassOop names after the PermGen removal Apr 4, 2024

openjdk bot added the rfr Pull request is ready for review label Apr 4, 2024

openjdk bot added graal graal-dev@openjdk.org serviceability serviceability-dev@openjdk.org hotspot hotspot-dev@openjdk.org labels Apr 4, 2024

rkennke suggested changes Apr 4, 2024

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		ldrw(scan_temp, Address(recv_klass, Klass::vtable_length_offset()));

		// %%% Could store the aligned, prescaled offset in the klassoop.

8329655: Cleanup KlassObj and klassOop names after the PermGen removal #18618

8329655: Cleanup KlassObj and klassOop names after the PermGen removal #18618

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