RFR (M): 8141141: Young and Old gen PLAB stats are similar in output with -XX:+PrintPLAB

[Thomas Schatzl]

Hi all,

  can I get reviews for the following change that tries to improve PLAB
logging output.

In particular, instead of:

[2,245s][debug  ][gc,plab] GC(33)  (allocated = 1 wasted = 0 unused = 0
used = 1 undo_waste = 0 region_end_waste = 0 regions filled = 0
direct_allocated = 0 failure_used = 0 failure_waste = 0)  (plab_sz = 0
desired_plab_sz = 258)
[2,245s][debug  ][gc,plab] GC(33)  (allocated = 1 wasted = 0 unused = 0
used = 1 undo_waste = 0 region_end_waste = 0 regions filled = 0
direct_allocated = 0 failure_used = 0 failure_waste = 0)  (plab_sz = 0
desired_plab_sz = 258)

The logging looks like:

[0.330s][debug][gc,plab  ] GC(0) Young PLAB allocation: allocated:
1825632B, wasted: 29424B, unused: 2320B, used: 1793888B, undo waste:
0B,
[0.330s][debug][gc,plab  ] GC(0) Young other allocation: region end
waste: 0B, regions filled: 2, direct allocated: 271520B, failure used:
0B, failure wasted: 0B
[0.330s][debug][gc,plab  ] GC(0) Young sizing: calculated: 358776B,
actual: 358776B
[0.330s][debug][gc,plab  ] GC(0) Old PLAB allocation: allocated:
427248B, wasted: 592B, unused: 368584B, used: 58072B, undo waste: 0B,
[0.330s][debug][gc,plab  ] GC(0) Old other allocation: region end
waste: 0B, regions filled: 1, direct allocated: 41704B, failure used:
0B, failure wasted: 0B
[0.330s][debug][gc,plab  ] GC(0) Old sizing: calculated: 11608B,
actual: 11608B

I.e. with the following changes:
- add "Young"/"Old" identifier to show "generation" 
- split information into multiple lines; the "other allocation" and
"sizing" are optional. "other allocation" is only printed when using
G1, "sizing" only when ResizePLAB is enabled 
- values are in bytes now (with units), not heapwords

I think it is a big improvement.

CR:
https://bugs.openjdk.java.net/browse/JDK-8141141
Webrev:
http://cr.openjdk.java.net/~tschatzl/8141141/webrev/
Testing:
jprt, existing plab logging test cases