How to Configure HugePages for Oracle Database on Linux

a) Setting up  memlock in /etc/security/limits.conf. Make this parameter slightly smaller than available physical memory ( 512G ).

oracle soft memlock 475830802
oracle hard memlock 475830802

b) Check memlock setting is effective by logging as oracle user.

$ ulimit -l
475830802

c) Copy shell script hugepages_settings.sh as per My Oracle Support (MOS) note 401749.1), and run this script as user oracle.

$chmod 744 ./hugepages_setting.sh  
$ ./hugepages_settings.sh
.
.
.
Recommended setting: vm.nr_hugepages = 86016


---
--- hugepages_settings.sh
---
---
#!/bin/bash
#
# hugepages_settings.sh
#
# Linux bash script to compute values for the
# recommended HugePages/HugeTLB configuration
# on Oracle Linux
#
# Note: This script does calculation for all shared memory
# segments available when the script is run, no matter it
# is an Oracle RDBMS shared memory segment or not.
#
# This script is provided by Doc ID 401749.1 from My Oracle Support 
# http://support.oracle.com

# Welcome text
echo "
This script is provided by Doc ID 401749.1 from My Oracle Support 
(http://support.oracle.com) where it is intended to compute values for 
the recommended HugePages/HugeTLB configuration for the current shared 
memory segments on Oracle Linux. Before proceeding with the execution please note following:
 * For ASM instance, it needs to configure ASMM instead of AMM.
 * The 'pga_aggregate_target' is outside the SGA and 
   you should accommodate this while calculating SGA size.
 * In case you changes the DB SGA size, 
   as the new SGA will not fit in the previous HugePages configuration, 
   it had better disable the whole HugePages, 
   start the DB with new SGA size and run the script again.
And make sure that:
 * Oracle Database instance(s) are up and running
 * Oracle Database 11g Automatic Memory Management (AMM) is not setup 
   (See Doc ID 749851.1)
 * The shared memory segments can be listed by command:
     # ipcs -m


Press Enter to proceed..."

read

# Check for the kernel version
KERN=`uname -r | awk -F. '{ printf("%d.%d\n",$1,$2); }'`

# Find out the HugePage size
HPG_SZ=`grep Hugepagesize /proc/meminfo | awk '{print $2}'`
if [ -z "$HPG_SZ" ];then
    echo "The hugepages may not be supported in the system where the script is being executed."
    exit 1
fi

# Initialize the counter
NUM_PG=0

# Cumulative number of pages required to handle the running shared memory segments
for SEG_BYTES in `ipcs -m | cut -c44-300 | awk '{print $1}' | grep "[0-9][0-9]*"`
do
    MIN_PG=`echo "$SEG_BYTES/($HPG_SZ*1024)" | bc -q`
    if [ $MIN_PG -gt 0 ]; then
        NUM_PG=`echo "$NUM_PG+$MIN_PG+1" | bc -q`
    fi
done

RES_BYTES=`echo "$NUM_PG * $HPG_SZ * 1024" | bc -q`

# An SGA less than 100MB does not make sense
# Bail out if that is the case
if [ $RES_BYTES -lt 100000000 ]; then
    echo "***********"
    echo "** ERROR **"
    echo "***********"
    echo "Sorry! There are not enough total of shared memory segments allocated for 
HugePages configuration. HugePages can only be used for shared memory segments 
that you can list by command:

    # ipcs -m

of a size that can match an Oracle Database SGA. Please make sure that:
 * Oracle Database instance is up and running 
 * Oracle Database 11g Automatic Memory Management (AMM) is not configured"
    exit 1
fi

# Finish with results
case $KERN in
    '2.2') echo "Kernel version $KERN is not supported. Exiting." ;;
    '2.4') HUGETLB_POOL=`echo "$NUM_PG*$HPG_SZ/1024" | bc -q`;
           echo "Recommended setting: vm.hugetlb_pool = $HUGETLB_POOL" ;;
    '2.6') echo "Recommended setting: vm.nr_hugepages = $NUM_PG" ;;
    '3.8') echo "Recommended setting: vm.nr_hugepages = $NUM_PG" ;;
    '3.10') echo "Recommended setting: vm.nr_hugepages = $NUM_PG" ;;
    '4.1') echo "Recommended setting: vm.nr_hugepages = $NUM_PG" ;;
esac

# End

d) Disable AMM by setting the values of both of the initialization parameters memory_target and memory_max_target to 0. Instead we use ASMM sga_target and sga_max_size for the SGA and pga_aggregate_target for PGA.

SQL> alter system set memory_target=0 scope=spfile;
System altered.
SQL> alter system set memory_max_target=0 scope=spfile;
System altered.
SQL> alter system set sga_target=xxxxxx scope=spfile;
System altered.
SQL> alter system set sga_max_size=xxxxxx scope=spfile;
System altered.
SQL> alter system set pga_aggregate_target =xxxxxx scope=spfile;

e) Modify file /etc/sysctl.conf,  and set the value of the vm.nr_hugepages parameter to the recommended value.

$cat /etc/sysctl.conf
...
...
vm.nr_hugepages = 86016

f) Shut down all the instances, and reboot the Linux server to make HugePages configuration effective.

$ grep ^Huge /proc/meminfo
HugePages_Total: 86016
HugePages_Free:   6557
HugePages_Rsvd:    492
HugePages_Surp: 0
Hugepagesize: 2048 kB

Please note the sum of the Hugepages_Free and HugePages_Rsvd values is likely to be smaller than the total SGA size because  the database instances allocate pages dynamically and proactively as required.

g) Check the database instances are using HugePages in Alert.log when instances starts up.

Starting ORACLE instance (normal)
************************ Large Pages Information *******************
Per process system memlock (soft) limit = UNLIMITED

Total Shared Global Region in Large Pages = 8194 MB (100%)

Large Pages used by this instance: 4097 (8194 MB)
Large Pages unused system wide = 61442 (120 GB)
Large Pages configured system wide = 86016 (168 GB)
Large Page size = 2048 KB
********************************************************************

 

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