Chapter 3. Configure Page Memory

Configure Page Memory for Red Hat Enterprise Linux

1. Set the Shared Memory Segment Size

   As root, set the maximum size of a shared memory segment in bytes; below we define this to be 32 GB:

   # echo "kernel.shmmax = 34359738368" >> /etc/sysctl.conf

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2. Set the Huge Pages

   The number of huge pages is set to the total amount of memory the JVM will consume (heap, meta space, thread stacks, native code) divided by the Hugepagesize. In Red Hat Enterprise Linux systems Hugepagesize is set to 2048 KB.

   1. The number of huge pages required can be determined by the following formula:

      Heap + Meta space + Native JVM Memory + (Number of Threads * Thread Stack Size)

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   2. Assuming a JVM with a 32 GB Heap, 2 GB of Meta space, a 512 MB native footprint, and 500 threads, each with a default size of 1 MB per thread, we have the following equation.

      32*(1024*1024*1024) + 2*(1024*1024*1024) + 512*(1024*1024) + (500 * 1024*1024)

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   3. The resulting value can now be converted to hugepages. Since there are 2048 KB in a single hugepage we perform the following:

      37568380928 / (2*1024*1024)

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   4. As root, set the number of huge pages determined from the previous steps to be allocated to the operating system:

      # echo "vm.nr_hugepages = 17914" >> /etc/sysctl.conf

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3. Assigned Shared Memory Permissions

   As root, set the ID of the user group that is allowed to create shared memory segments using the hugetlb_shm_group file. This value should match the group id of the user running the JVM:

   # echo "vm.hugetlb_shm_group = 500" >> /etc/sysctl.conf

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4. Update the Resource Limits

   To allow a user to lock the required amount of memory, update the resource limits in the /etc/security/limits.conf file by adding the following:

   jboss      soft   memlock      unlimited
   jboss      hard   memlock      unlimited

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   This change allows the user jboss to lock the system’s available memory.

5. Configure Authentication using PAM

   Linux’s PAM handles authentication for applications and services. Ensure that the configured system resource limits apply when using su and sudo as follows:

   • Configure PAM for su

     Add the following line to the /etc/pam.d/su file:

     session    required   pam_limits.so

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   • Configure PAM for sudo

     Add the following line to the /etc/pam.d/sudo file:

     session    required   pam_limits.so

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6. Reboot the system for the changes to take effect. Since Huge Pages allocate a contiguous block of memory these must be allocated at system boot; attempts to claim these dynamically while the system is running may result in system hangs if the memory is unable to be reclaimed.

Procedure: Configure Page Memory for the JVM

1. Set the Heap Size

   Use the -Xms and -Xmx parameters to set the minumum and maximum heap sizes for your JVM, as discussed in Java Virtual Machine Settings.

2. Enable Large Pages

   Enabled large pages for the JVM by adding the following parameter, as discussed in Java Virtual Machine Settings:

   -XX:+UseLargePages

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