JVM Linux Large Pages

[zloster]

Investigate how to enable and if the large memory pages help?

-XX:+UseHugeTLBFS

This option for Linux is the equivalent of specifying -XX:+UseLargePages. This option is disabled by default. This option pre-allocates all large pages up-front, when memory is reserved; consequently the JVM cannot dynamically grow or shrink large pages memory areas; see -XX:UseTransparentHugePages if you want this behavior.

For more information, see "Large Pages".

-XX:+UseLargePages

Enables the use of large page memory. By default, this option is disabled and large page memory is not used.

For more information, see "Large Pages".

Source: http://docs.oracle.com/javase/8/docs/technotes/tools/unix/java.html

[zloster]

Nice short writing about this feature: https://shipilev.net/jvm-anatomy-park/2-transparent-huge-pages/

Case in point, using 4 TB (terabyte, with a T) heap:

$ time java -Xms4T -Xmx4T -XX:-UseTransparentHugePages -XX:+AlwaysPreTouch
real    13m58.167s
user    43m37.519s
sys     1011m25.740s
$ time java -Xms4T -Xmx4T -XX:+UseTransparentHugePages -XX:+AlwaysPreTouch
real    2m14.758s
user    1m56.488s
sys     73m59.046s

Committing and freeing 4 TB sure takes a while!