RFR: JDK-8204685: Abstraction for TLAB dummy object

[Roman Kennke]

Am 12.06.2018 um 15:58 schrieb Aleksey Shipilev:
> On 06/11/2018 06:02 PM, Roman Kennke wrote:
>> Similar to how object allocations should be owned by the GC, so does
>> TLAB dummy object 'allocation'. TLABs and PLABs are filling their
>> remaining blocks with dummy objects. GCs like Shenandoah might need a
>> slightly differet layout for this, and therefore we need an abstraction.
>>
>> The proposed change adds a new virtual method
>> CollectedHeap::fill_with_dummy_object(), the default implementation
>> calls the existing CH::fill_with_object() from TLAB and PLAB like it was
>> done before.
>>
>> Tested: hotspot-tier1, Shenandoah tests with appropriate impl
>>
>> http://cr.openjdk.java.net/~rkennke/JDK-8204685/webrev.00/
> 
> I have doubts about setting "zap = false" unconditionally. As far as I can see, zapping is enabled
> for debug builds only anyway, so we better keep it "true".
> 
>   82 size_t PLAB::retire_internal() {
>   83   size_t result = 0;
>   84   if (_top < _hard_end) {
>   85     Universe::heap()->fill_with_dummy_object(_top, _hard_end, false);  <--- change to true?
>   86     result += invalidate();
>   87   }
>   88   return result;
>   89 }
>   90
>   91 void PLAB::add_undo_waste(HeapWord* obj, size_t word_sz) {
>   92   Universe::heap()->fill_with_dummy_object(obj, obj + word_sz, false); <--- change to true?
>   93   _undo_wasted += word_sz;
>   94 }
> 

Right.
http://cr.openjdk.java.net/~rkennke/JDK-8204685/webrev.01/

Good now?

Thanks for reviewing!
Roman


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