RFR: 8329203: Parallel: Investigate Mark-Compact for Full GC to decrease memory usage [v2]

[Albert Mingkun Yang]

On Mon, 6 May 2024 18:08:50 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Refactor Parallel full-gc to use the same algorithm (mark-compact) as Serial and G1 full-GC. This removes the obj-end bitmap. When GC threads are few, the old implementation can be more efficient because it requires fewer heap iterations. The new full-GC implementation, on the other hand, is more scalable because it introduces more phases (`forward_to_new_addr` and `adjust_pointers`) that can partition work effectively.
>> 
>> The diff is rather large, so reading the new code directly from `invoke_no_policy` is probably easier.
>> 
>> Test: tier1-6; some improvement in Dacapo-h2, CacheStresser, but no difference in specjbb2015, specjvm2008.
>
> Albert Mingkun Yang 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:
> 
>  - review
>  - Merge branch 'master' into pgc-full-gc
>  - pgc-full-gc

> Have you also run the micros test/micro/org/openjdk/bench/vm/gc/systemgc/ on it?

~40% improvement on `OneBigObject.gc` and ~10% regression on `AllLive.gc`. Small or no diff for the rest.

Both baseline and new-impl have pros and cons. No single winner for all scenarios.

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PR Review: https://git.openjdk.org/jdk/pull/19101#pullrequestreview-2041365519