RFR: 8305895: Implement JEP 450: Compact Object Headers (Experimental) [v5]

[Roman Kennke]

On Fri, 30 Aug 2024 07:42:39 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> Yes. This silent setting of UseCompactObjectHeaders ended up hiding why we got CDS failures. I would also suggest that we change this to FLAG_SET_ERGO.
>
> Seems we run all into the same thoughts :)
> 
> I added
> 
> Suggestion:
> 
>     FLAG_SET_DEFAULT(UseCompactObjectHeaders, false);
>     warning("Compact object headers require a java heap size smaller than %zu (given: %zu). "
>                  "Disabling compact object headers.", max_narrow_heap_size * HeapWordSize, max_heap_size);

That %zu is SIZE_FORMAT, right? This should probably use proper_unit_for_byte_size()/byte_size_in_proper_unit().

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/20677#discussion_r1750215510