Use LDR_CNTRL in AIX to use 64KB page sizes.

[rmnattas]

We can improve performance on AIX by setting LDR_CNTRL to use 64KB pages by default.

LDR_CNTRL=TEXTPSIZE=64K@DATAPSIZE=64K@STACKPSIZE=64K@SHMPSIZE=64K

This is proposed to OpenJDK https://bugs.openjdk.org/browse/JDK-8252802 but rejected.

• JDK8: Use LDR_CNTRL on AIX to use 64KB pages ibmruntimes/openj9-openjdk-jdk8#739
• JDK11: Use LDR_CNTRL on AIX to use 64KB pages ibmruntimes/openj9-openjdk-jdk11#760
• JDK17: Use LDR_CNTRL on AIX to use 64KB pages ibmruntimes/openj9-openjdk-jdk17#330
• JDK21: Use LDR_CNTRL on AIX to use 64KB pages and modify removeAixExpectedVars ibmruntimes/openj9-openjdk-jdk21#134
• JDK22: Use LDR_CNTRL on AIX to use 64KB pages and modify removeAixExpectedVars ibmruntimes/openj9-openjdk-jdk22#30
• JDKNext: Use LDR_CNTRL on AIX to use 64KB pages and modify removeAixExpectedVars ibmruntimes/openj9-openjdk-jdk#749

[rmnattas]

@pshipton @zl-wang

[pshipton]

https://bugs.openjdk.org/browse/JDK-8252802 wasn't committed. The status is withdrawn, and the PR openjdk/jdk#17906 (comment) was closed due to that comment.

What testing have we done on this change locally?

[rmnattas]

Tested couple workloads locally and it may have helped somewhat or stayed the same, with not significant impact on memory usage (positive or negative), hence no significant implication. Also pLinux already uses 64KB everywhere by default.

[pshipton]

That doesn't seem like a strong justification to go ahead with the change and the potential risks. Everything forked from the JVM will have the same settings.

[zl-wang]

In the past (java7 time), we set it anyway. It was lost without our knowing when the build was moved to Bangalore. On POWER6/7, it had substantial performance benefit. On newer processor(s), the benefit seemed less (2-3%). No other implications expected. @pshipton

[pshipton]

Pls run internal builds with all the test suites.

[pshipton]

Besides the testing, the change should include an option to control the behavior, so a user or dev can turn it off for diagnostics, if it's causing problems, or the change isn't desired. An example similar option is -XX:[+/-]UseZlibNX.
https://github.com/ibmruntimes/openj9-openjdk-jdk/blob/openj9/src/java.base/unix/native/libjli/java_md.c#L390

[zl-wang]

that sounds reasonable. we only set it when -XX:-YYY is not set.