RFR (S) 8078438: Interpreter should support conditional card marks (UseCondCardMark)

Andrew Haley aph at redhat.com
Tue Apr 28 13:13:51 UTC 2015


On 04/28/2015 02:06 PM, Mikael Gerdin wrote:
> 
> On 2015-04-28 14:45, Andrew Haley wrote:
>> On 04/28/2015 11:56 AM, Thomas Schatzl wrote:
>>> Somewhat related, note that C2 adds a MemBarRelease before the actual
>>> card table store (see StoreCMNode) I think to ensure store ordering (the
>>> card mark must be visible after the reference write). So the given
>>> aarch64 code seems to be missing something already.
>>
>> I don't think it's missing anything.  It has the barrier in the correct
>> place when G1 is in use, and CMS isn't supposed to need one.
> 
> I think it does depend on StoreStore ordering, the field write must be 
> visible if the dirty card byte is visible.

Hmm.  We were told otherwise here before.  Does the code which scans
the card table use a load barrier after each read of the card?  If not
the StoreStore won't have any effect anyway.

Andrew.



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