RFR: 8361099: Shenandoah: Improve heap lock contention by using CAS for memory allocation [v20]

[Xiaolong Peng]

On Tue, 6 Jan 2026 02:04:04 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

>> Xiaolong Peng has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 265 commits:
>> 
>>  - Merge branch 'openjdk:master' into cas-alloc-1
>>  - Fix build error after merging from tip
>>  - Merge branch 'master' into cas-alloc-1
>>  - Merge branch 'master' into cas-alloc-1
>>  - Some comments updates as suggested in PR review
>>  - Fix build failure after merge
>>  - Expend promoted from ShenandoahOldCollectorAllocator
>>  - Merge branch 'master' into cas-alloc-1
>>  - Address PR comments
>>  - Merge branch 'openjdk:master' into cas-alloc-1
>>  - ... and 255 more: https://git.openjdk.org/jdk/compare/de81d389...cf13b7b5
>
> src/hotspot/share/gc/shenandoah/shenandoahAllocator.cpp line 364:
> 
>> 362:   _free_set->partitions()->decrease_used(ALLOC_PARTITION, total_free_bytes);
>> 363:   _free_set->partitions()->increase_region_counts(ALLOC_PARTITION, total_regions_to_unretire);
>> 364:   accounting_updater._need_update = true;
> 
> Here is where you know which tallies have been affected by this operation.  This is where you should specialize the calls to freeset recompute_total_used() and recompute_total_affiliated().  Either call those from here, or add parameters to your accounting_updater object so that you do not have to overcompute each operation.

This is not the only place, there are many other places in the allocation code path as well, I can specialize the calls to  recompute_total_used and recompute_total_affiliated in the places, but that will make the code necessary rambling, I'd rather to solve this issue and simplify it in https://bugs.openjdk.org/browse/JDK-8373371.

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PR Review Comment: https://git.openjdk.org/jdk/pull/26171#discussion_r2673820942