RFR: 8267185: Add string deduplication support to ParallelGC [v3]

[Albert Mingkun Yang]

On Mon, 16 Aug 2021 11:44:19 GMT, Ivan Walulya <iwalulya at openjdk.org> wrote:

>> Hi all,
>> 
>> Please review this change to add string deduplication support to ParallelGC.
>> 
>> Testing: All string deduplication tests, and Tier 1-5.
>
> Ivan Walulya has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fix indentation

The rest look fine.

src/hotspot/share/gc/parallel/psStringDedup.cpp line 33:

> 31:   // reached the deduplication age threshold, i.e. has not previously been a
> 32:   // candidate during its life in the young generation.
> 33:   return PSParallelCompact::space_id(cast_from_oop<HeapWord*>(java_string)) > PSParallelCompact::old_space_id &&

I wonder if the space-id comparison can be replaced with sth like `PSScavenge::is_obj_in_young(java_string)`; we are checking if this `java_string` live in young-gen, right?

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PR: https://git.openjdk.java.net/jdk/pull/5085