RFR: 8338440: Parallel: Improve fragmentation mitigation in Full GC [v5]

[Zhengyu Gu]

On Mon, 26 Aug 2024 17:20:18 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Extend `SplitInfo` to support more fine-grained splitting to mitigate the fragmentation issue during full GC. Added comments and diagrams in the process.
>> 
>> For easier review, it's best to start with `SplitInfo` and then proceed to see how it is constructed in `summarize_split_space` and consumed in `first_src_addr`. The accompanying diagrams should help create a clear mental image.
>> 
>> With this patch, the exec time of `runtime/ClassInitErrors/TestOutOfMemoryDuringInit.java` using Parallel drops from ~30s to ~8s, the same as other GCs, and gc-log shows similar number of GC cycles as well.
>> 
>> Test: tier1-8, systemgc micro bm, CacheStress, dacapo, specjbb2005, specjvm2008
>
> Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   assert

LGTM

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Marked as reviewed by zgu (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/20590#pullrequestreview-2263397509