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

[Thomas Schatzl]

Hi all,

  can I have comments and reviews for the following change to move
G1Allocator::_summary_bytes_used to a more fitting place?

The problem from my POV is, that the member
G1Allocator::_summary_bytes_used, that contains the number of bytes held
by the heap outside of the allocators is located within G1Allocator.

That sounds odd, particularly because G1Allocator actually never uses
it, it's managed completely by G1CollectedHeap.

Before the addition of the G1ArchiveAllocator one could have made the
argument that G1Allocator holds all memory contained in the heap, but
this is not true any more: the memory occupied by G1ArchiveAllocator
needs to be added to the total sum of all managed space anyway, so
moving _summary_bytes_used out of G1Allocator seems sensible (to me).

I talked to StefanJ about this change who originally moved
_summary_used_bytes into G1Allocator, and we could not find an argument
for keeping _summary_used_bytes in G1Allocator.

This allows us to also refine the responsibilities of G1Allocator a
little more, to be the owner of the current allocation areas (regions)
only.

CR:
https://bugs.openjdk.java.net/browse/JDK-8131319

Webrev:
http://cr.openjdk.java.net/~tschatzl/8131319/webrev/

Testing:
jprt

Thanks,
  Thomas