Hi folks,
according to some notes on the net (e.g. [1]) openjdk11 is aware of
the container limits for calculating default heap size and some
other internal parameters. Apparently this works very well for
Docker. Sample:
# docker run -ti --rm --cpus 2 -m 4G debian
root@c526096eb86e:/# apt update; apt install -y default-jdk
:
:
done.
done.
Processing triggers for libgdk-pixbuf2.0-0:amd64 (2.38.1+dfsg-1) ...
root@c526096eb86e:/# cat /sys/fs/cgroup/memory/memory.limit_in_bytes
4294967296
root@c526096eb86e:/# cat /sys/fs/cgroup/memory/memory.memsw.limit_in_bytes
8589934592
root@c526096eb86e:/# java -XX:MaxRAMPercentage=20.0 -XX:MinRAMPercentage=10.0
-XX:+PrintFlagsFinal -version | egrep MaxHeap\|RAMPercentage\|Container
double InitialRAMPercentage = 1.562500
{product} {default}
uintx MaxHeapFreeRatio = 70
{manageable} {default}
size_t MaxHeapSize = 859832320
{product} {ergonomic}
double MaxRAMPercentage = 20.000000
{product} {command line}
double MinRAMPercentage = 10.000000
{product} {command line}
bool PreferContainerQuotaForCPUCount = true
{product} {default}
bool UseContainerSupport = true
{product} {default}
openjdk version "11.0.6" 2020-01-14
OpenJDK Runtime Environment (build 11.0.6+10-post-Debian-1deb10u1)
OpenJDK 64-Bit Server VM (build 11.0.6+10-post-Debian-1deb10u1, mixed mode,
sharing)
Check the MaxHeapSize. 20% of 4 GByte, as requested.
For an LXC container running Debian and the same OpenJDK I get:
root@debian10:~# cat /sys/fs/cgroup/memory/memory.limit_in_bytes
4294967296
root@debian10:~# cat /sys/fs/cgroup/memory/memory.memsw.limit_in_bytes
4294967296
root@debian10:~# java -XX:MaxRAMPercentage=20.0 -XX:MinRAMPercentage=10.0
-XX:+PrintFlagsFinal -version | egrep MaxHeap\|RAMPercentage\|Container
double InitialRAMPercentage = 1.562500
{product} {default}
uintx MaxHeapFreeRatio = 70
{manageable} {default}
size_t MaxHeapSize = 13511950336
{product} {ergonomic}
double MaxRAMPercentage = 20.000000
{product} {command line}
double MinRAMPercentage = 10.000000
{product} {command line}
bool PreferContainerQuotaForCPUCount = true
{product} {default}
bool UseContainerSupport = true
{product} {default}
openjdk version "11.0.6" 2020-01-14
OpenJDK Runtime Environment (build 11.0.6+10-post-Debian-1deb10u1)
OpenJDK 64-Bit Server VM (build 11.0.6+10-post-Debian-1deb10u1, mixed mode,
sharing)
memory.limit_in_bytes is 4 GByte, but Java gives me a MaxHeapSize of
0.20 * 64GByte.
Of course I don't want to blame you for bugs in OpenJDK, but I wonder
how comes? Are there some mysterious params set in a Docker container,
but missing in LXC?
Every insightful comment is highly appreciated
Harri
1:
https://stackoverflow.com/questions/54292282/clarification-of-meaning-new-jvm-memory-parameters-initialrampercentage-and-minr/54297753#54297753
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