RFR/RFC: Make OOM-during-evacuation race-free

[Aleksey Shipilev]

On 10/23/2017 02:44 PM, Roman Kennke wrote:
> I would like to get your comments on the patch, and approvals from everybody (Christine, Aleksey,
> Zhengyu and Roland) before pushing. In particular, I'd be happy if Aleksey could run some
> read-barrier heavy gc-benchmarks to measure the (worst-case) impact of masking in the read-barriers.
> 
> http://cr.openjdk.java.net/~rkennke/safe-oom-during-evac/webrev.02/

While the trick is interesting, I don't like it very much that we are extending the read barriers.
It *should* have the non-zero performance impact -- because even adding the NOPs had -- and I can
run the tests after Roland's change lands and makes RBs more frequent.

The performance data you have is very noisy to capture <10% regressions. I think it makes sense to
discuss the change only when we have accurate performance data on hand. Otherwise, we have to
consider alternatives that do not touch the RBs.

Thanks,
-Aleksey