RFR: 8067499: G1SATBCardTableModRefBS should not inherit from CardTableModRefBSForCTRS

Thomas Schatzl thomas.schatzl at oracle.com
Wed Dec 17 14:53:22 UTC 2014


Hi,

On Wed, 2014-12-17 at 01:14 -0500, Kim Barrett wrote:
> Please review this change to G1SATBCardTableModRefBS to derive from
> CardTableModRefBS rather than CardTableModRefBSForCTRS.
> 
> Note: I will need a sponsor for this change.
[..]
> 
> A different way of addressing the remembered set location would have been to
> change G1CollectedHeap to derive from CollectedHeap rather than SharedHeap,
> and that's a change that has been suggested as a technical debt cleanup.  That
> change would have required similar changes to G1 code, plus a number of other
> changes.  This move of remembered set support can be viewed as a step toward
> changing the heap hierarchy.

I talked to Tony Printezis about this once, and he mentioned that perm
gen support has been the main reason to let G1CollectedHeap inherit from
SharedHeap and not from CollectedHeap.

> It may be that the G1 barrier set shouldn't derive from CardTableModRefBS
> either; CardTableModRefBS provides a lot of stuff that G1 doesn't use or need,
> some of which has to be overridden or called for compatibility.
> Alternatively, it might be that some things presently in CardTableModRefBS
> should be moved down to CardTableModRefBSForCTRS.  But again, that larger
> refactoring would require more changes, and this move of remembered set
> support and shift of the G1 barrier set base class can be viewed as a step
> toward that larger refactoring.

Agree - thanks for the cleanup. Looks good.

Thomas




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