Java cannot allocate RAM - Trying to add Confluence to an existing Jira installation

[Sys Admin]

I have a self hosted Jira / Jira Service Desk installation on a debian 9 VM that has been working fine.  I only have 3 users and <10 projects so it isn't a big installation.

I decided to try Confluence so I used the linux installer, followed the installation istructions and used the express option. All went well, but Confluence will not run.  This is what is in the catalina.out log file:

OpenJDK 64-Bit Server VM warning: INFO: os::commit_memory(0x00000000c0000000, 1073741824, 0) failed; error='Cannot allocate memory' (errno=12)

I am at a bit of a loss to know how to fix this.

The Debiasn virtual machine has 4vCPU and 16GB RAM.  Looking at the running system on average it has a 20% load, and is using 8GB RAM.

According to the existing JIRA installation, the Java VM Memory Statistics are:

Total Memory 1820 MB
Free Memory 798 MB
Used Memory 1022 MB  or 44% free.

So what am I missing? 

Any explanations/suggestions welcome!

[Sys Admin · Accepted solution]

Well, it looks like I have answered my own question.

I Installed the default Debian Java JDK using apt install default-jdk.

Then I added a line to the setenv.sh script for java, and the setjre.sh script for confluence:

JRE_HOME="/usr/lib/jvm/default-java/jre"

And both are working happily.

[Sys Admin]

I just realized that Confluence is invoking OpenJDK, whereas JIRA is invoking Oracle.  Can they both happily work on the same server?

Or, can I get them both to use the same JRE, situated elsewhere?

Thanks