RFR: 8225255: Make SATB qset lock-free

[Kim Barrett]

> On Jun 20, 2019, at 4:50 AM, Aleksey Shipilev <shade at redhat.com> wrote:
> 
> On 6/19/19 8:10 PM, Kim Barrett wrote:
>> Making the SATB queue set's completed buffer list lock-free makes the
>> management of the count and process_completed_buffers flag trickier.
>> […]  That will be
>> looked at later; see JDK-8226337.
> 
> Yes, I think promptness in SATB buffer processing is more beneficial for pauses, especially when
> filtering blows out the already-marked objects. IIRC, my Shenandoah experiments shown that by the
> end of concurrent mark there are hardly any new oops come from SATB. In fact, the filtering gets too
> effective for its own good: if you are following up with G1 SATB performance work, I'd suggest
> fixing JDK-8205353 first.

Thanks for the reminder about that RFE.  I’ve added some links between it and others.

There’s a whole little cluster of issues in this vicinity.  Figuring out how to attack these
and in what order or possibly combining or splitting up issues differently is going to require
some careful thought.

>> Webrev:
>> http://cr.openjdk.java.net/~kbarrett/8225255/open.00/
> 
> Shenandoah parts look good. It also passes hotspot_gc_shenandoah for me.
> 
> -- 
> Thanks,
> -Aleksey

Thanks.