RFR: 8371783: Refactor GCCause in VM_CollectForMetadataAllocation

[Albert Mingkun Yang]

On Thu, 13 Nov 2025 10:08:36 GMT, Joel Sikström <jsikstro at openjdk.org> wrote:

> Hello,
> 
> We should improve how we use and set GCCause in VM_CollectForMetadataAllocation to make it more clear when reading the code what is going on.
> 
> When constructing a VM_CollectForMetadataAllocation operation, we pass in a GCCause, which is not always the cause that is used, since we might also have to clear soft references as a last resort if earlier collection attemps is not enough to free up memory.
> 
> The GCCauseSetter at the start of this operation is also redundant as subsequent calls to initiate a GC set the cause themselves.
> 
> Testing:
> * Oracle's tier1-3

src/hotspot/share/gc/shared/gcVMOperations.cpp line 210:

> 208:   SvcGCMarker sgcm(SvcGCMarker::FULL);
> 209: 
> 210:   CollectedHeap* heap = Universe::heap();

This `heap` var can be moved down now, I think.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28287#discussion_r2541693878