RFR: 8308231: Faster MemAllocator::Allocation checks for verify/notification [v3]

[Aleksey Shipilev]

On Mon, 22 May 2023 21:06:01 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Aleksey Shipilev 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 eight additional commits since the last revision:
>> 
>>  - Reshuffle and simplify
>>  - Merge branch 'master' into JDK-8308231-memalloc-check-faster
>>  - Touch up comment
>>  - Merge branch 'master' into JDK-8308231-memalloc-check-faster
>>  - Hide more stuff
>>  - Touchups
>>  - Branch
>>  - Fix
>
> src/hotspot/share/gc/shared/memAllocator.cpp line 98:
> 
>> 96: 
>> 97:       if ((is_real_allocation || _tlab_end_reset_for_sample) &&
>> 98:           JvmtiExport::should_post_sampled_object_alloc()) {
> 
> The same check is done inside the caller already.
> 
> On this note, I think all checks using info outside `class Allocation` should not be present on this level. (Ofc, this is very subjective.)

This is a fast-path code, and it is extremely sensitive to the overheads of the actual calls. So I made a point to check the pre-conditions before calling them. It is much less sensitive to the overheads for the methods that are already protected by `is_real_allocations`, but for others the condtions are pulled to the fast path.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14019#discussion_r1201818427