RFR: 8315219: G1: Improve allocator pathological case where it keeps doing direct allocations instead of retiring a PLAB [v2]

[Thomas Schatzl]

On Wed, 30 Aug 2023 10:12:02 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Ivan Walulya has updated the pull request incrementally with three additional commits since the last revision:
>> 
>>  - nit
>>  - nit
>>  - Thomas Review
>
> src/hotspot/share/gc/g1/g1Allocator.cpp line 389:
> 
>> 387:     may_throw_away_buffer(words_remaining, plab_word_size)) {
>> 388: 
>> 389:     guarantee(words_remaining <= required_in_plab, "must be");
> 
> What's the intend of this check? Also, if the two are equal, plab-alloc should have succeeded, so one shouldn't retire the current plab.

This is a (pre-existing) sanity check (that is correct but a little imprecise because in the == case we would not reach here) and could (and probably should because it is somewhat confusing) be removed.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15482#discussion_r1310062211