RFR: 8305895: Implement JEP 450: Compact Object Headers (Experimental) [v11]

[Thomas Stuefe]

On Wed, 11 Sep 2024 11:29:38 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

>> Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix FullGCForwarding initialization
>
> src/hotspot/share/memory/metaspace/metablock.hpp line 52:
> 
>> 50:   bool is_empty() const { return _base == nullptr; }
>> 51:   bool is_nonempty() const { return _base != nullptr; }
>> 52:   void reset() { _base = nullptr; _word_size = 0; }
> 
> Is this function really necessary? According to my IDE it's only used in tests and even then the `MetaBlock` isn't used afterwards (so it has no effect).

see test_clms.cpp, test_random function, used in two places there.

> src/hotspot/share/memory/metaspace/metaspaceArena.hpp line 84:
> 
>> 82:   // between threads and needs to be synchronized in CLMS.
>> 83: 
>> 84:   const size_t _allocation_alignment_words;
> 
> Nit: Document this? All other members are documented.

ok

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PR Review Comment: https://git.openjdk.org/jdk/pull/20677#discussion_r1762993378
PR Review Comment: https://git.openjdk.org/jdk/pull/20677#discussion_r1762995731