RFR: 8324649: Shenandoah: refactor implementation of free set [v2]

[Kelvin Nilsen]

On Fri, 26 Jan 2024 18:56:23 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> Kelvin Nilsen has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Remove unnecessary change related to debugging
>
> src/hotspot/share/gc/shenandoah/shenandoahFreeSet.cpp line 550:
> 
>> 548:   }
>> 549: 
>> 550:   if (alloc_capacity(r) < PLAB::min_size() * HeapWordSize) {
> 
> Why not `TLAB::min_size`?

Good question.  You've caused me to dig a little to respond:

size_t PLAB::min_size() {
  // Make sure that we return something that is larger than AlignmentReserve                                                                                 
  return align_object_size(MAX2(MinTLABSize / HeapWordSize, (size_t)oopDesc::header_size())) + CollectedHeap::lab_alignment_reserve();
}

There is no TLAB::min_size() as far as I can tell.  There is MinTLABSize (default 2K unless redefined on command line), but that value appears to get rounded up by alignment in the definition of PLAB::min_size().  I think PLAB:min_size() is what we want here (and elsewhere within this source file).

What do you think?

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PR Review Comment: https://git.openjdk.org/jdk/pull/17561#discussion_r1468082037