Disable use of HugePages

[megazone23]

Java -version output

openjdk version "1.8.0_222"
OpenJDK Runtime Environment (build 1.8.0_222-b10)
Eclipse OpenJ9 VM (build openj9-0.15.1, JRE 1.8.0 Linux amd64-64-Bit Compressed References 20190717_368 (JIT enabled, AOT enabled)
OpenJ9 - 0f66c64
OMR - ec782f26
JCL - f147086df1e based on jdk8u222-b10)

Summary of problem

When huge pages are configured in Linux. Need setting to prevent java from using huge pages, on our servers Java is causing other applications which require huge pages from working. For HotSpot on Windows and Linux huge pages are disabled by default. It seems OpenJ9 even with out the -Xlp argument it is still reserving and allocating huge pages.

Diagnostic files

To replicate use the following program:

public class Sleep {
    public static void main(String[] args) throws NumberFormatException, InterruptedException {
        Thread.sleep(Long.parseLong(args[0]));

    }
}

With a Linux machine configured with huge pages you will see the following:

# cat /proc/meminfo | grep Huge
AnonHugePages:         0 kB
HugePages_Total:     571
HugePages_Free:      514
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB

If you runt the program you will see the HugePages_Rsvd increase and the HugePages_Free shows usage:

java -cp . Sleep 1000000

# cat /proc/meminfo | grep Huge
AnonHugePages:         0 kB
HugePages_Total:     571
HugePages_Free:      513
HugePages_Rsvd:      127
HugePages_Surp:        0
Hugepagesize:       2048 kB

[dmitripivkine]

@megazone23 You can use -Xlp4k or -Xlp:objectheap:pagesize=4k -Xlp:codecache:pagesize=4k to disable using of Huge pages explicitly as a temporary solution (I know this is a little bit weird).
Meanwhile there is a discussion how to align HotSpot and OpenJ9 Large Page related options. You can take part in it if you like. It is unlikely default behaviour of OpenJ9 would be changed to not use Large Pages due better performance "out of the box"

[megazone23]

I tried your recommendation and worked. Thanks!

I would be interested in the discussion. How do I access it?

[DanHeidinga]

I would be interested in the discussion. How do I access it?

Check #8671 which is where most of the higher level conversation is occurring. Implementation details are mostly broken out / being broken into pull requests associated with that.

[DanHeidinga]

Closing as discussion has dropped off