On Sat, 13 Dec 2025 02:04:27 GMT, Albert Mingkun Yang <[email protected]> wrote:
>> src/hotspot/share/gc/parallel/psParallelCompact.cpp line 1070:
>>
>>> 1068:
>>> size_policy->sample_old_gen_used_bytes(MAX2(pre_gc_values.old_gen_used(),
>>> old_gen->used_in_bytes()));
>>> 1069:
>>> 1070: if (UseAdaptiveSizePolicy) {
>>
>> I think this code block could raise heap size don't expand in some specific
>> case, maybe you should optimize it. @albertnetymk
>
> @SilenceZheng66 Could you elaborate the issue, ideally, in a JBS ticket? (A
> reproducer/gc-log would be nice, but detailed description works as well.)
@albertnetymk Sure. I will give detailed description here.
GC：PS MarkSweep、PS Scavenge
JVM configuraton:
-Xmx2g
-Xms256M
-XX:MetaspaceSize=256m
-XX:MaxMetaspaceSize=256m
-XX:+PrintGCDateStamps
-XX:+PrintGCDetails
-XX:-UseAdaptiveSizePolicy
-XX:+PrintAdaptiveSizePolicy
-XX:+HeapDumpBeforeFullGC
-XX:+HeapDumpOnOutOfMemoryError
-XX:HeapDumpPath=export/Logs/
-Xloggc:/export/Logs/gclogs.log
JVM version：25.191-b12, although it's an old version without maintenance, I
find out the problem might still in the latest version.
Problem Description:
When starting a application(like SpringBoot), objects loading to VM
continuously, my CPU usage suddenly began to skyrocket, followed by a full GC
lasting over ten minutes with more than 2,700 occurrences. Examining the GC
logs revealed that prior to the full GC, several successful young GC events had
taken place until the old generation was completely filled. I read the source
code and find out when -XX:-UseAdaptiveSizePolicy was set, VM thread can't
expand psOldGen, only GC worker can expand psOldGen's size in that condition. I
assume that the transition from the younger generation to the older generation
has been successful, so that GC worker's expansion was not reached, that made
long term full GC happened.
Check List:
1. Container has enough place for heap expansion
2. Xms and Xmx were setting differently, same configuration in Serial GC can
raise heap expansion
GC log sample:
// Full GC Starting
[PSYoungGen: 76276K->10735K(76288K)] 244793K->181638K(251392K), 0.0078092 secs]
[Times: user=0.04 sys=0.00, real=0.01 secs]
2025-12-10T14:11:58.663+0800: 24.604: [Heap Dump (before full gc): , 0.0000482
secs]2025-12-10T14:11:58.663+0800: 24.604: [Full GC (Ergonomics) [PSYoungGen:
10735K->0K(76288K)] [ParOldGen: 170902K->173351K(175104K)]
181638K->173351K(251392K), [Metaspace: 107770K->107770K(1146880K)], 0.5258832
secs] [Times: user=1.82 sys=0.00, real=0.52 secs]
2025-12-10T14:11:59.268+0800: 25.210: [Heap Dump (before full gc): , 0.0000684
secs]2025-12-10T14:11:59.269+0800: 25.210: [Full GC (Ergonomics) [PSYoungGen:
65536K->0K(76288K)] [ParOldGen: 173351K->174276K(175104K)]
238887K->174276K(251392K), [Metaspace: 109096K->109096K(1148928K)], 0.3031080
secs] [Times: user=1.10 sys=0.01, real=0.30 secs]
2025-12-10T14:11:59.710+0800: 25.651: [Heap Dump (before full gc): , 0.0000752
secs]2025-12-10T14:11:59.710+0800: 25.651: [Full GC (Ergonomics) [PSYoungGen:
65536K->0K(76288K)] [ParOldGen: 174276K->174980K(175104K)]
239812K->174980K(251392K), [Metaspace: 110351K->110351K(1148928K)], 0.3664816
secs] [Times: user=1.21 sys=0.00, real=0.37 secs]
// Full GC Running
2025-12-10T14:12:52.408+0800: 78.350: [Heap Dump (before full gc): , 0.0000535
secs]2025-12-10T14:12:52.409+0800: 78.350: [Full GC (Ergonomics) [PSYoungGen:
65536K->64255K(76288K)] [ParOldGen: 174893K->174893K(175104K)]
240429K->239149K(251392K), [Metaspace: 148330K->148330K(1183744K)], 0.2442300
secs] [Times: user=0.68 sys=0.00, real=0.25 secs]
2025-12-10T14:12:52.656+0800: 78.598: [Heap Dump (before full gc): , 0.0000711
secs]2025-12-10T14:12:52.657+0800: 78.598: [Full GC (Ergonomics) [PSYoungGen:
65536K->64333K(76288K)] [ParOldGen: 174893K->174893K(175104K)]
240429K->239227K(251392K), [Metaspace: 148379K->148379K(1183744K)], 0.2102640
secs] [Times: user=0.53 sys=0.02, real=0.21 secs]
2025-12-10T14:12:52.871+0800: 78.813: [Heap Dump (before full gc): , 0.0000622
secs]2025-12-10T14:12:52.872+0800: 78.813: [Full GC (Ergonomics) [PSYoungGen:
65534K->64252K(76288K)] [ParOldGen: 174893K->174893K(175104K)]
240428K->239146K(251392K), [Metaspace: 148488K->148488K(1183744K)], 0.2125166
secs] [Times: user=0.54 sys=0.00, real=0.22 secs]
// Full GC Ending
2025-12-10T14:32:47.691+0800: 1273.632: [Heap Dump (before full gc): ,
0.0000943 secs]2025-12-10T14:32:47.691+0800: 1273.633: [Full GC (Ergonomics)
[PSYoungGen: 65536K->24273K(76288K)] [ParOldGen: 174627K->174626K(175104K)]
240163K->198899K(251392K), [Metaspace: 152567K->152567K(1187840K)], 0.3627505
secs] [Times: user=1.12 sys=0.00, real=0.37 secs]
2025-12-10T14:35:18.172+0800: 1424.113: [Heap Dump (before full gc): ,
0.0001014 secs]2025-12-10T14:35:18.172+0800: 1424.114: [Full GC (Ergonomics)
[PSYoungGen: 65536K->9012K(76288K)] [ParOldGen: 174626K->174852K(175104K)]
240162K->183865K(251392K), [Metaspace: 152611K->152611K(1187840K)], 0.2574051
secs] [Times: user=0.63 sys=0.00, real=0.26 secs]
2025-12-10T14:38:49.044+0800: 1634.986: [Heap Dump (before full gc): ,
0.0001049 secs]2025-12-10T14:38:49.045+0800: 1634.987: [Full GC (Ergonomics)
[PSYoungGen: 65536K->0K(76288K)] [ParOldGen: 174852K->133113K(175104K)]
240388K->133113K(251392K), [Metaspace: 152680K->152680K(1187840K)], 0.3655573
secs] [Times: user=1.01 sys=0.00, real=0.36 secs]
2025-12-10T14:42:49.842+0800: 1875.784: [GC (Allocation Failure)
AdaptiveSizePolicy::update_averages: survived: 1671680 promoted: 0 overflow:
false
If you need other details just let me know, thx!
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/25000#discussion_r2619293977
