RFR: 8278568: Consolidate filler objects

[Albert Mingkun Yang]

On Mon, 13 Dec 2021 11:42:42 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

> In PSPromotionLAB exists some code that fills unused tails of promotion LABs, which is semantically the same as the CollectedHeap::fill* family of methods. They can be consolidated.
> 
> We also have ContiguousSpace::allocate_temporary_filler() which does the same, but is unused and can be removed. 
> 
> Testing:
>  - [x] hotspot_gc
>  - [x] tier1
>  - [ ] tier2
>  - [ ] tier3

Just two minor comments/suggestions.

src/hotspot/share/gc/parallel/psPromotionLAB.cpp line 79:

> 77:   // so they can always fill with an array.
> 78:   HeapWord* tlab_end = end() + CollectedHeap::min_dummy_object_size();
> 79:   CollectedHeap::fill_with_object(top(), tlab_end, DEBUG_ONLY(true) NOT_DEBUG(false));

Using `trueInDebug` would be clearer.

src/hotspot/share/gc/shared/collectedHeap.hpp line 292:

> 290: 
> 291:   virtual void fill_with_dummy_object(HeapWord* start, HeapWord* end, bool zap);
> 292:   static size_t min_dummy_object_size();

I wonder if `constexpr` works here.

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Marked as reviewed by ayang (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/6814