RFR: 8253815: Remove unused HeapRegionManager::_num_committed from SA

[Chris Plummer]

On Tue, 29 Sep 2020 18:29:57 GMT, Stefan Johansson <sjohanss at openjdk.org> wrote:

> While doing some refactoring I wanted to move HeapRegionManager::_num_committed and realized that I needed to update
> the SA. After some looking around it turns out that it is unused and I can remove the numCommittedField from the
> HeapRegionManager class in the SA.   Local build and test looks good and running tier1 and some svc-testing to ensure I
> haven't missed anything.

Changes requested by cjplummer (Reviewer).

src/hotspot/share/gc/g1/vmStructs_g1.hpp line 56:

> 54:                                                                               \
> 55:   nonstatic_field(HeapRegionManager, _regions,          G1HeapRegionTable)    \
> 56:   nonstatic_field(HeapRegionManager, _num_committed,    uint)                 \

If this field is remaining in hotspot, it should also remain in vmStructs. Although SA does not need to explicitly know
about this field to function properly, SA can be used to dump hotspot objects, and can only dump objects whose types
are in vmStructs, and for those types can only display the fields that are also in vmStructs.

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PR: https://git.openjdk.java.net/jdk/pull/408