RFR (S): 8244815: Always log MMU information in G1

[Thomas Schatzl]

Hi all,

   can I have reviews for this change that adds MMU logging for all 
pauses, not only when it is violated?

This makes the logging similar to JFR events which are posted always too.

Ie. currently G1 prints

[95.616s][info ][gc,mmu        ] GC(2932) MMU target violated: 10.5ms 
(10.0ms/11.0ms)

at info level if G1 did not keep MMU goals in the last pause.

This change adds the message

[82.315s][debug][gc,mmu        ] GC(2598) MMU target: 7.3ms (10.0ms/11.0ms)

at debug level even when MMU is kept. This helps with analyzing current MMU.

There is some a bit ugly code to select the correct message level. Maybe 
there is a better way. An alternative would be to move the message to 
debug level always?

CR:
https://bugs.openjdk.java.net/browse/JDK-8244815
Webrev:
http://cr.openjdk.java.net/~tschatzl/8244815/webrev/
Testing:
hs-tier1-3, eyeballing local logs

Thanks,
   Thomas