RFR (XXS): 8149442 : MonitorInUseLists should be on by default, deflate idle monitors taking too long

[Rickard Bäckman]

Looks good.

On 04/01, David Simms wrote:
> 
> Greetings,
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8149442
> Webrev: http://cr.openjdk.java.net/~dsimms/8149442/
> 
> Safe-point's "deflate_idle_monitors" (clean up task during
> Safepoint::begin()), constantly scans all monitors, the entire
> population. Setting MonitorInUseLists to true by default would seem
> prudent, as the it reduces the scan to "InUse" thread lists.
> Reduction in "deflate idle monitor" execution time of up to a
> magnitude.
> 
>    There are certain applications (notably SPECjbb2013 use of ForkJoin)
>    whose Java lock monitor total populations are quite high, but the
>    actual number of in use monitors is low.
> 
>    Why these total populations grow so large, further work to reduce
>    "deflate idle monitor" operations, is beyond the scope of this bug
>    (see JDK-7021979 & JDK-8153224).
> 
> Testing: no regressions spotted on the following benchmarks:
> 
>  * SpecJbb2005
>  * SpecJbb2008
>  * SpecJbb2013
>  * Volano
> 
> 
> 
> Cheers
> / David Simms
/R