Currently G1 assigns a thread per failed evacuated region. This can in effect serialize the whole process as often (particularly with region pinning) there is only one region to fix up.

Try to improve parallelism when walking over the regions by e.g. recording potential entry points with live object starts when evacuation failure happens for sub-areas of the region during evacuation failure handling.

Note that the BOT should NOT be used as it is not created for young gen regions; using it would recreate it at that point which is basically a full region walk.


Latest implementation scans regions in chunks to bring parallelism, it's based on JDK-8278917 which changes to uses prev bitmap to mark evacuation failure objs.



(I can not upload the attachments.)
Here's the summary of performance data based on latest implementation, basically, it brings better and stable performance than baseline at "Post Evacuate Cleanup 1/remove self forwardee" phase. (Although some regression is spotted when calculate the results in geomean, becuase one pause time from baseline is far too small than others.)

The performance benefit trend is:
 - pause time (Post Evacuate Cleanup 1) is decreased from 76.79% to 2.28% for average time, from 71.61% to 3.04% for geomean, when G1EvacuationFailureALotCSetPercent is changed from 2 to 90 (-XX:ParallelGCThreads=8)
 - pause time (Post Evacuate Cleanup 1) is decreased from 63.84% to 15.16% for average time, from 55.41% to 12.45% for geomean, when G1EvacuationFailureALotCSetPercent is changed from 2 to 90 (-XX:ParallelGCThreads=<default=123>)
( Other common Evacuation Failure configurations are:
-XX:+G1EvacuationFailureALot -XX:G1EvacuationFailureALotInterval=0 -XX:G1EvacuationFailureALotCount=0 )


(unit is ms, please ignore the too precise float number, I guess it should be due to copying from excel)
============= -XX:ParallelGCThreads=8 ==============
-XX:G1EvacuationFailureALotCSetPercent=2
5.785714286 1.342857143 76.79% // AVG
3.491874057 0.991334526 71.61% // GEOMEAN
-XX:G1EvacuationFailureALotCSetPercent=5
6.457142857 5.257142857 18.58% // AVG
3.751329198 4.842453032 -29.09% // GEOMEAN
-XX:G1EvacuationFailureALotCSetPercent=10
7.7 5.857142857 23.93% // AVG
6.438810941 4.01726936 37.61% // GEOMEAN

-XX:G1EvacuationFailureALotCSetPercent=20
24.58571429 19.61428571 20.22% // AVG
23.91174748 19.30619931 19.26% // GEOMEAN

-XX:G1EvacuationFailureALotCSetPercent=30
38.94285714 36.62857143 5.94% // AVG
37.68215788 34.95941805 7.23% // GEOMEAN

-XX:G1EvacuationFailureALotCSetPercent=50
61.64285714 58.01428571 5.89% // AVG
58.48164395 54.11292376 7.47% // GEOMEAN

-XX:G1EvacuationFailureALotCSetPercent=70
82.91428571 79.92857143 3.60% // AVG
77.74442286 74.19262861 4.57% // GEOMEAN

-XX:G1EvacuationFailureALotCSetPercent=90
96.02857143 93.84285714 2.28% // AVG
89.42483883 86.70240129 3.04% // GEOMEAN



============= -XX:ParallelGCThreads=<default=123> ==============
-XX:G1EvacuationFailureALotCSetPercent=2
5.728571429 2.071428571 63.84% // AVG
4.55615823 2.031440622 55.41% // GEOMEAN

-XX:G1EvacuationFailureALotCSetPercent=5
9.371428571 3.4 63.72% // AVG
8.921695255 3.189298958 64.25% // GEOMEAN

-XX:G1EvacuationFailureALotCSetPercent=10
10.37142857 4.842857143 53.31% // AVG
9.36881833 4.583811393 51.07% // GEOMEAN

-XX:G1EvacuationFailureALotCSetPercent=20
15.18571429 10.72857143 29.35% // AVG
14.81067789 10.2772486 30.61% // GEOMEAN

-XX:G1EvacuationFailureALotCSetPercent=30
21.01428571 18.74285714 10.81% // AVG
20.70456459 18.26632857 11.78% // GEOMEAN

-XX:G1EvacuationFailureALotCSetPercent=50
34.58571429 30.07142857 13.05% // AVG
33.57743078 28.85928625 14.05% // GEOMEAN

-XX:G1EvacuationFailureALotCSetPercent=70
47.17142857 40.34285714 14.48% // AVG
45.28903319 39.17734325 13.49% // GEOMEAN

-XX:G1EvacuationFailureALotCSetPercent=90
58.71428571 49.81428571 15.16% // AVG
54.65737668 47.85414364 12.45% // GEOMEAN