RFR: 8319650: Improve heap dump performance with class metadata caching [v3]

[Aleksey Shipilev]

On Thu, 9 Nov 2023 14:25:00 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
>> 
>>  - Limit the table size
>>  - Merge branch 'master' into JDK-8319650-heapdump-cache-meta
>>  - Fix
>
> src/hotspot/share/services/heapDumper.cpp line 813:
> 
>> 811: };
>> 812: 
>> 813: class DumperClassCacheTable : public StackObj {
> 
> Technically it's a ValueObj inside a StackObj, so don't really need to have StackObj here. To me, that it's means that you're going to use it as a local variable in a method, when it's really embedded in StackObj.  One can argue all ways on this though, it's just my opinion.

Yeah. What is the proper idiom for "I do not want this to be allocated (in C heap or anywhere else) without NMT knowing"? `StackObj` is the closest I can get nowadays, I think. `ValueObj` is gone since JDK 11: https://bugs.openjdk.org/browse/JDK-8199282

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PR Review Comment: https://git.openjdk.org/jdk/pull/16545#discussion_r1388127736