RFR (S): 8131319: Move G1Allocator::_summary_bytes_used back to G1CollectedHeap

[Tom Benson]

Hi again,

Forgot to reply to this part:
>> Actually, the PLAB allocators do exactly that every time a region is
>> retired via updating the actual bytes copied in the collector policy
>> which is then later added to the total.
>>
>> I will look into this since it seems it is not only me not liking the
>> "if (archive_allocator != NULL) { ... }" copy&paste code here as it
>> might be easy to forget.
>    so I looked through the code again, and one way of passing on the
> amount of memory actually used would be to return that value in
> G1Allocator::end_archive_alloc_range(), to be added by the caller to the
> _summary_bytes_used.

That would work with archive regions used as they are today, where there 
will not be a GC while one is 'active.'   But if we want to continue to 
allow that possibility, doing it there won't eliminate the 'clear_use' 
calls.   I think calling g1h->increase_used would eliminate both the 
'clear_use' calls and the check to see if _archive_allocator exists when 
computing the used size,  while still allowing GCs while an archive 
region was active.
Really, I guess this could be the subject of a separate change later.
Tom