Java 9,10,11 slow to start on zLinux

[pshipton]

Java 9,10,11 are slow to start on zLinux.

This problem seems to be the cause of #2329.

The default -Xmx for Java 9 and later is 25% of the physical memory. Startup time varies, but on a zLinux machine with 64GB, startup time without specifying -Xmx can be a second or more. Explicitly set -Xmx512m and its much faster. The time varies from run to run, and OS to OS. Explicitly setting an -Xmx which is equivalent to the default may also speed up the startup time.

[pshipton]

May also affect other Linux platforms to some extent. The problem was originally mentioned in #1888.

[charliegracie]

@pshipton can you please show an example of where specifying the exact same value for -Xmx as what would be picked without one shows a difference in startup performance? I would like to see verbose:gc logs to verify that the maximum and initial heap values are exactly the same byte value.

[pshipton]

Double checked, setting an -Xmx which is equivalent to the default does not speed up the startup time.

[pshipton]

One of the problems is fixed by eclipse-omr/omr#2743, however there is still a problem outstanding. The QUICK memory allocation algorithm can fail to find a suitable candidate but then it falls back to a brute force search which also won't find any suitable memory and can be very slow.

[pshipton]

The remaining problem appears resolved by eclipse-omr/omr#2796.
See #2329 for details.

[keithc-ca]

Fixed via eclipse-omr/omr#2796.

[pshipton]

For the record, eclipse-openj9/openj9-omr#12 merged eclipse-omr/omr#2796 to the v0.9.0-release branch.