RFR: 8272611: Use parallel heap inspection when print classhisto info in gc log

[Thomas Schatzl]

On Wed, 18 Aug 2021 07:35:50 GMT, Bin Liao <github.com+3094961+buddyliao at openjdk.org> wrote:

> This patch helps to enhance the heap inspection with parallel threads when print classhisto info in gc log.
> 
> I have built it on linux x86_64 and run test-tier1 successfully
> 
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Changes requested by tschatzl (Reviewer).

src/hotspot/share/gc/shared/collectedHeap.cpp line 551:

> 549:     ResourceMark rm;
> 550:     LogStream ls(lt);
> 551:     uint parallel_thread_num = MAX2<uint>(1, (uint)os::initial_active_processor_count() * 3 / 8);

Where do the magic numbers for the formula come from? Please consider using the ergonomically determined number of threads (`CollectedHeap::safepoint_workers()->active_workers()`)? (Maybe change this in another CR as other reviewers think is better, looking whether there is a significant difference between these numbers)

src/hotspot/share/gc/shared/collectedHeap.cpp line 552:

> 550:     LogStream ls(lt);
> 551:     uint parallel_thread_num = MAX2<uint>(1, (uint)os::initial_active_processor_count() * 3 / 8);
> 552:     VM_GC_HeapInspection inspector(&ls, false /* ! full gc */, parallel_thread_num);

Pre-existing: the comment next to a bool constant in a parameter list should show the name of the parameter, i.e. s/! full_gc/request_full_gc/. Maybe change this as appropriate in other callers too.

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PR: https://git.openjdk.java.net/jdk/pull/5158