RFR: 8257145: Performance regression with -XX:-ResizePLAB after JDK-8079555

[Stefan Johansson]

On Fri, 27 Nov 2020 09:39:01 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> Hi,
>> 
>> this is the continuation of the review of the implementation for:
>> 
>> https://bugs.openjdk.java.net/browse/JDK-8257145
>
> src/hotspot/share/gc/g1/g1CollectedHeap.cpp line 1409:
> 
>> 1407:   _bytes_used_during_gc(0),
>> 1408:   _archive_allocator(NULL),
>> 1409:   _survivor_evac_stats("Young", YoungPLABSize * ParallelGCThreads, PLABWeight),
> 
> Lgtm, will do some perf measurements and get back to you.
> Could you add a comment like the following in the G1EvacStats constructor?
> 
> // desired_plab_size_ should be the total PLAB size for all threads.

Just one note, if we run with `UseDynamicNumberOfGCThreads` the PLAB size might still be "resized" between GCs if they use different number of threads. This is still an improvement since the old value is wrong and will give a way to small PLAB size. But we might want to look at a solution that will always return a fixed PLAB size with `-ResizePLAB`.

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PR: https://git.openjdk.java.net/jdk/pull/1474