[RHEL] What is the maximum support for hugepages

문제

• What is the maximum support for HugePages on my system?
• What is the maximum size HugePages that I can use?
• Is there a limit to the HugePages size that I can use?

환경

• Red Hat Enterprise Linux 5
• x86_64 architecture

해결

• How does the kernel interpret hugepage size?

  • The system will read the HugePage size as 2MB by default. There are only a
    few architectures that have the ability to change this (powerpc for example)

• Does having more HugePages equal better performance?

  • The HugePage amount will be relevant to the the amount of
    memory that you want to allocate to your system to operate your oracle application.

  • The Linux kernel has support for multiple HugePage sizes and allows for use of multiple different
    sizes at the same time; however, the available sizes are dependent on the architecture.

  • The x86(_64) system size of each HugePage will be in /proc/meminfo; i.e. 2 MiB.

Example:

# grep -i hugepage /proc/meminfo

HugePages_Total:   500
HugePages_Free:    500
HugePages_Rsvd:      0
Hugepagesize:     2048 kB

• NUMBER_OF_HUGEPAGES = ( SGA + PGA + (20k * #_of_Oracle_processes)) / 2MB

• Enabling hugepages for use with Oracle Database:
  https://access.redhat.com/knowledge/solutions/69306

• Tuning Red Hat Enterprise Linux for Oracle and Oracle RAC:
  https://access.redhat.com/knowledge/solutions/39188

• Oracle Tuning Guide:

  • Red Hat Enterprise Linux 5 for Oracle 9i and 10g Databases:
    https://access.redhat.com/knowledge/docs/en-US/Red_Hat_Enterprise_Linux/5/html/Tuning_and_Optimizing_Red_Hat_Enterprise_Linux_for_Oracle_9i_and_10g_Databases/

  • Red Hat Enterprise Linux 5 for Oracle Database 11g Release 2:
    http://www.redhat.com/rhecm/rest-rhecm/jcr/repository/collaboration/jcr:system/jcr:versionStorage/ee6fe0000a0526020f35498ae39e9939/12/jcr:frozenNode/rh:resourceFile