Huge Pages on Oracle Linux

Environment

Oracle Linux Server release 7.3
Oracle database 11.2, 12.1

Quick checking

# cat /proc/sys/vm/nr_hugepages

2054

or

# cat /proc/meminfo | grep Huge
AnonHugePages:         0 kB
HugePages_Total:    2054
HugePages_Free:      546
HugePages_Rsvd:      542
HugePages_Surp:        0
Hugepagesize:       2048 kB




checking if transparent huge pages are disabled

# cat /sys/kernel/mm/transparent_hugepage/enabled

always madvise [never]

Viewing database 12.1 alert log

**********************************************************************

Mon Oct 16 12:28:54 2017

Dump of system resources acquired for SHARED GLOBAL AREA (SGA)

Mon Oct 16 12:28:54 2017

 Per process system memlock (soft) limit = 128G

Mon Oct 16 12:28:54 2017

 Expected per process system memlock (soft) limit to lock

 SHARED GLOBAL AREA (SGA) into memory: 2050M

Mon Oct 16 12:28:54 2017

 Available system pagesizes:

  4K, 2048K

Mon Oct 16 12:28:54 2017

 Supported system pagesize(s):

Mon Oct 16 12:28:54 2017

  PAGESIZE  AVAILABLE_PAGES  EXPECTED_PAGES  ALLOCATED_PAGES  ERROR(s)

        4K       Configured               3               3        NONE

     2048K             2054            1025            1025        NONE

**********************************************************************




Viewing database 11.2 alert log

************************ Large Pages Information *******************

Per process system memlock (soft) limit = 128 GB




Total Shared Global Region in Large Pages = 2050 MB (100%)




Large Pages used by this instance: 1025 (2050 MB)

Large Pages unused system wide = 4 (8192 KB)

Large Pages configured system wide = 2054 (4108 MB)

Large Page size = 2048 KB

********************************************************************

If number of Huge pages is less than required, than SGA will use both page types. Database 12.1 aler.log:

  PAGESIZE  AVAILABLE_PAGES  EXPECTED_PAGES  ALLOCATED_PAGES  ERROR(s)

        4K       Configured               3          187704        NONE

     2048K              659            1025             658        NONE




Simplified setup

1. Have the memlock user limit set in /etc/security/limits.conf file. Set the value (in KB) slightly smaller than total RAM (90%) , at least it must be bigger than HugePages size.
*   soft   memlock    14680064
*   hard   memlock    14680064
Atentu! If you use systemd to auto startup databases, systemd ignores limits.conf. You need to add the following to a service unit file
[Service]
LimitMEMLOCK=infinity
LimitNOFILE=65535



2. Get the required number of pages from alert.log (EXPECTED_PAGES) or by running Oracle script hugepages_settings.sh (Doc ID 401749.1)




3. edit vm.nr_hugepages in /etc/sysctl.conf as root

4. to reload the parameters, reboot Linux or use sysctl -p




Proper setup and more info

HugePages on Oracle Linux 64-bit (Doc ID 361468.1)

HugePages on Linux: What It Is... and What It Is Not... (Doc ID 361323.1)

Oracle Linux: Shell Script to Calculate Values Recommended Linux HugePages / HugeTLB Configuration (Doc ID 401749.1)

Oracle 12.2 Documentation: Administering Oracle Database on Linux