RFR: 8332448: Make SpaceMangler inherit AllStatic

[Kim Barrett]

On Fri, 17 May 2024 09:29:07 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Extract the state for `top` out of `SpaceMangler`. Users (Serial and Parallel GC) already tracks the top before/after GC. The "real" change in this PR are only two places: `serialFullGC.cpp` and `PSParallelCompact::post_compact`.
> 
> Test: tier1-5

Changes requested by kbarrett (Reviewer).

src/hotspot/share/gc/serial/serialFullGC.cpp line 370:

> 368:       HeapWord* new_top = get_compaction_top(i);
> 369:       // Reset top and unused memory
> 370:       space->set_top(new_top);

I'd rather the new_top variable declaration was after the comment rather than before.

src/hotspot/share/gc/shared/spaceDecorator.cpp line 32:

> 30: 
> 31: // Simply mangle the MemRegion mr.
> 32: void SpaceMangler::mangle_region(MemRegion mr) {

SpaceMangler::mangle_region should be debug-only rather than not-product, both conceptually, and
because it has no effect in non-debug builds.

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PR Review: https://git.openjdk.org/jdk/pull/19279#pullrequestreview-2067015569
PR Review Comment: https://git.openjdk.org/jdk/pull/19279#discussion_r1607265118
PR Review Comment: https://git.openjdk.org/jdk/pull/19279#discussion_r1607273088