Alibaba reported:


I was running jdk11u Shenandoah on specjvm2008, and found the passive mode has a leak-like behaviour:

$java -Xmx24g -Xms24g -XX:ParallelGCThreads=1 -XX:+UseShenandoahGC -XX:+UnlockDiagnosticVMOptions -XX:ShenandoahGCMode=passive -Xlog:gc*=debug:file=512sp.log -jar SPECjvm2008.jar -ict -coe -i 1 derby

$grep 'Pause .*ms' 512sp.log
[63.407s][info ][gc ] GC(0) Pause Degenerated GC (Outside of Cycle) 23344M->15824M(24576M) 6994.533ms
[71.029s][info ][gc ] GC(1) Pause Degenerated GC (Outside of Cycle) 23343M->15520M(24576M) 7325.687ms
[80.319s][info ][gc ] GC(2) Pause Degenerated GC (Outside of Cycle) 23343M->11720M(24576M) 8721.156ms
[88.396s][info ][gc ] GC(3) Pause Degenerated GC (Outside of Cycle) 23343M->4176M(24576M) 7549.126ms
[94.300s][info ][gc ] GC(4) Pause Degenerated GC (Outside of Cycle) 23343M->4192M(24576M) 5216.467ms
[99.941s][info ][gc ] GC(5) Pause Degenerated GC (Outside of Cycle) 23343M->4200M(24576M) 4984.741ms
[105.506s][info ][gc ] GC(6) Pause Degenerated GC (Outside of Cycle) 23343M->4208M(24576M) 4901.316ms
[111.339s][info ][gc ] GC(7) Pause Degenerated GC (Outside of Cycle) 23343M->4216M(24576M) 5175.875ms
[117.154s][info ][gc ] GC(8) Pause Degenerated GC (Outside of Cycle) 23343M->4224M(24576M) 5134.298ms
[123.078s][info ][gc ] GC(9) Pause Degenerated GC (Outside of Cycle) 23343M->4232M(24576M) 5255.877ms
[129.249s][info ][gc ] GC(10) Pause Degenerated GC (Outside of Cycle) 23343M->4232M(24576M) 5505.492ms
[135.258s][info ][gc ] GC(11) Pause Degenerated GC (Outside of Cycle) 23343M->4240M(24576M) 5355.191ms
[141.378s][info ][gc ] GC(12) Pause Degenerated GC (Outside of Cycle) 23343M->4248M(24576M) 5487.325ms
[147.217s][info ][gc ] GC(13) Pause Degenerated GC (Outside of Cycle) 23343M->4256M(24576M) 5214.325ms
[152.963s][info ][gc ] GC(14) Pause Degenerated GC (Outside of Cycle) 23343M->4264M(24576M) 5083.129ms
[158.798s][info ][gc ] GC(15) Pause Degenerated GC (Outside of Cycle) 23343M->4272M(24576M) 5162.959ms
[164.950s][info ][gc ] GC(16) Pause Degenerated GC (Outside of Cycle) 23343M->4280M(24576M) 5475.542ms
[170.856s][info ][gc ] GC(17) Pause Degenerated GC (Outside of Cycle) 23343M->4288M(24576M) 5222.228ms
[177.007s][info ][gc ] GC(18) Pause Degenerated GC (Outside of Cycle) 23343M->4304M(24576M) 5300.388ms
[182.809s][info ][gc ] GC(19) Pause Degenerated GC (Outside of Cycle) 23343M->4312M(24576M) 4833.105ms
[189.589s][info ][gc ] GC(20) Pause Degenerated GC (Outside of Cycle) 23344M->4312M(24576M) 5441.911ms
[195.528s][info ][gc ] GC(21) Pause Degenerated GC (Outside of Cycle) 23343M->4320M(24576M) 5262.478ms
[201.654s][info ][gc ] GC(22) Pause Degenerated GC (Outside of Cycle) 23343M->4328M(24576M) 5491.649ms
[208.601s][info ][gc ] GC(23) Pause Degenerated GC (Outside of Cycle) 23343M->4336M(24576M) 6293.675ms
[214.483s][info ][gc ] GC(24) Pause Degenerated GC (Outside of Cycle) 23343M->4344M(24576M) 5259.813ms
[220.657s][info ][gc ] GC(25) Pause Degenerated GC (Outside of Cycle) 23343M->4352M(24576M) 5533.361ms
[227.005s][info ][gc ] GC(26) Pause Degenerated GC (Outside of Cycle) 23343M->4352M(24576M) 5712.247ms
[233.210s][info ][gc ] GC(27) Pause Degenerated GC (Outside of Cycle) 23343M->4368M(24576M) 5580.975ms
[239.202s][info ][gc ] GC(28) Pause Degenerated GC (Outside of Cycle) 23343M->4368M(24576M) 5379.766ms
[245.565s][info ][gc ] GC(29) Pause Degenerated GC (Outside of Cycle) 23343M->4376M(24576M) 5714.096ms
[251.450s][info ][gc ] GC(30) Pause Degenerated GC (Outside of Cycle) 23343M->4384M(24576M) 5250.005ms
[257.447s][info ][gc ] GC(31) Pause Degenerated GC (Outside of Cycle) 23343M->4392M(24576M) 5354.806ms
[263.840s][info ][gc ] GC(32) Pause Degenerated GC (Outside of Cycle) 23343M->4400M(24576M) 5716.993ms
[270.792s][info ][gc ] GC(33) Pause Degenerated GC (Outside of Cycle) 23343M->4408M(24576M) 6264.228ms
[277.201s][info ][gc ] GC(34) Pause Degenerated GC (Outside of Cycle) 23343M->4408M(24576M) 5743.778ms
[283.828s][info ][gc ] GC(35) Pause Degenerated GC (Outside of Cycle) 23343M->4416M(24576M) 5973.385ms
[291.227s][info ][gc ] GC(36) Pause Degenerated GC (Outside of Cycle) 23343M->4424M(24576M) 6587.729ms
[298.153s][info ][gc ] GC(37) Pause Degenerated GC (Outside of Cycle) 23343M->4432M(24576M) 6122.285ms
[304.722s][info ][gc ] GC(38) Pause Degenerated GC (Outside of Cycle) 23343M->4440M(24576M) 5938.363ms
[311.097s][info ][gc ] GC(39) Pause Degenerated GC (Outside of Cycle) 23343M->4448M(24576M) 5737.377ms
[317.710s][info ][gc ] GC(40) Pause Degenerated GC (Outside of Cycle) 23343M->4448M(24576M) 5994.975ms
[323.969s][info ][gc ] GC(41) Pause Degenerated GC (Outside of Cycle) 23343M->4456M(24576M) 5624.046ms
[330.910s][info ][gc ] GC(42) Pause Degenerated GC (Outside of Cycle) 23343M->4464M(24576M) 6298.006ms
[337.761s][info ][gc ] GC(43) Pause Degenerated GC (Outside of Cycle) 23343M->4472M(24576M) 6248.352ms
[344.369s][info ][gc ] GC(44) Pause Degenerated GC (Outside of Cycle) 23343M->4480M(24576M) 5947.428ms
[351.096s][info ][gc ] GC(45) Pause Degenerated GC (Outside of Cycle) 23343M->4488M(24576M) 6094.857ms
[357.776s][info ][gc ] GC(46) Pause Degenerated GC (Outside of Cycle) 23343M->4496M(24576M) 6048.758ms
[364.830s][info ][gc ] GC(47) Pause Degenerated GC (Outside of Cycle) 23343M->4504M(24576M) 6418.273ms
[370.804s][info ][gc ] GC(48) Pause Degenerated GC (Outside of Cycle) 23343M->4512M(24576M) 5348.577ms
[376.787s][info ][gc ] GC(49) Pause Degenerated GC (Outside of Cycle) 23344M->4520M(24576M) 5339.928ms
[383.407s][info ][gc ] GC(50) Pause Degenerated GC (Outside of Cycle) 23343M->4528M(24576M) 5942.465ms
[389.858s][info ][gc ] GC(51) Pause Degenerated GC (Outside of Cycle) 23343M->4536M(24576M) 5801.355ms
[396.714s][info ][gc ] GC(52) Pause Degenerated GC (Outside of Cycle) 23343M->4544M(24576M) 6190.560ms
[403.752s][info ][gc ] GC(53) Pause Degenerated GC (Outside of Cycle) 23343M->4560M(24576M) 6226.817ms
[410.816s][info ][gc ] GC(54) Pause Degenerated GC (Outside of Cycle) 23343M->4560M(24576M) 6400.091ms
[417.651s][info ][gc ] GC(55) Pause Degenerated GC (Outside of Cycle) 23343M->4568M(24576M) 6206.848ms
[424.040s][info ][gc ] GC(56) Pause Degenerated GC (Outside of Cycle) 23343M->4576M(24576M) 5774.497ms
[431.115s][info ][gc ] GC(57) Pause Degenerated GC (Outside of Cycle) 23343M->4584M(24576M) 6433.645ms
[437.740s][info ][gc ] GC(58) Pause Degenerated GC (Outside of Cycle) 23343M->4592M(24576M) 5980.660ms



The heap seems to grow slowly, and the pause time tends to grow too.
The jdk16 or 17 version appears okay (with constant after-gc heap size).

I wonder if there is a known reason?