RFR: 8305995: Footprint regression from JDK-8224957 [v4]

[Tobias Hartmann]

On Fri, 14 Apr 2023 20:51:35 GMT, Kirill A. Korinsky <duke at openjdk.org> wrote:

>> This is a fix for the regression introduced by da43cb5e463069cf4dafb262664f0d3d7c2e0eac in fix 8224957.
>> 
>> This regression was found while attempting to migrate an application from JDK 1.8 to JDK 17, by running internal benchmarks, and while investigating abnormal memory usage for about 4 times more from one of them.
>> 
>> The regression appears in the JMH benchmark, which builds a huge tree which contains boxed integers from 0 to a few thousand. A tree has very complex structure and the same objects are reused a lot.
>> 
>> When an `integer` is found it's collected as `Integer` and unboxed inside the collector callback.
>> 
>> This benchmark was run with `ParallelGC` on different JVMs: `JDK 1.8.0_362`, `JDK 11.0.18`, `JDK 13.0.13`, `JDK 15.0.9`, `JDK 17.0.6`, `JDK 19.0.2` and `JDK 20`. This allows to see that something has changed between 13 and 15, and that the memory footprint for this code has increased from `3152` to `11828` bytes per operation.
>> 
>> After that I've done a `git bisect` which allows me to locate the introducer.
>> 
>> So the current fix reduces the memory footprint on the local root 425ef0685c584abec80454fbcccdcc6db6558f93 to `2960` bytes per operation.
>
> Kirill A. Korinsky has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix the copyright year

Looks good to me too. Thanks for fixing this!

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Marked as reviewed by thartmann (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/13453#pullrequestreview-1387910597