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

[Stefan Johansson]

On Tue, 29 Sep 2020 19:43:45 GMT, Chris Plummer <cjplummer 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.
>
> 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.

The field will remain for now, but the plan is to refactor it into a new class. The new class is not needed by the SA
and I would really like to avoid having to add unused and untested code to the SA. To simplify this coming change I
want to remove this from the SA straight away.

Even without this coming change I would vote for removing this type of unused code from the SA. I don't think being
able to dump the value is worth enough compared to the maintenance cost of keeping it in.

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