Container-aware heap sizing for OpenJDK

[Man Cao]

Hi Volker,

Yes, we are aware of "sun.gc.collector.{0,1,2}.time", and they only account
for pause time.
Accounting for only pause time does not accurately measure GC overhead for
collectors with a large portion of concurrent work.
This is also the reason why heuristics based on -XX:GCTimeRatio are broken
for G1.
https://mail.openjdk.org/pipermail/hotspot-gc-dev/2021-May/035241.html has
a related discussion.

Yes, the CPU time metric sums up CPU time from all parallel GC worker
threads and concurrent GC threads.
I just found https://bugs.openjdk.org/browse/JDK-8291753 which exports CPU
time via JFR events. However, it seems to only account for CPU time spent
during pauses, which does not cover all concurrent work. I'll do more
digging and follow up when I create an RFE.

-Man
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