Improving the scalability of the evac OOM protocol

[Aleksey Shipilev]

On 10/4/22 14:56, Nick Gasson wrote:
> I tried fixing this in a fairly simple way by replicating the counter N
> times on separate cache lines (N=64, somewhat arbitrarily).  See the
> draft patch below:
> 
> https://github.com/nick-arm/jdk/commit/ca78e77f0c6
> 
> Each thread hashes to a particular counter based on its Thread*.

Yes, stripped counter works here fine.

> I've also tested SPECjbb on a fastdebug build with
> -XX:+ShenandoahOOMDuringEvacALot and didn't see any errors.

make test TEST=hotspot_gc_shenandoah exercises evac paths a lot, consider running it on affected 
platforms.

> I experimented with taking this to its logical conclusion and giving
> each thread its own counter in ShenandoahThreadLocalData, but it's
> difficult to avoid races with thread creation and this simple approach
> seems to give most of the benefit anyway.
> 
> Any thoughts on this?

Looks very good, please PR this. There are minor improvements we can do to this patch.

-- 
Thanks,
-Aleksey