一、什么时候配置when
IF
SGA >= 2GB AND sessions >= 500

THEN
enabling HugePages becomes a requirement on Linux 64-bit system.

二、怎么配置How to Configure HugePages

The configuration steps below will guide you to do a persistent system configuration where you would need to do a complete reboot of the system. Please plan your operations accordingly:

Step 1: Have the memlock user limit set in /etc/security/limits.conf file. Set the value (in KB) slightly smaller than installed RAM. e.g. If you have 64GB RAM installed, you may set:

* soft memlock 60397977* hard memlock 60397977

There is no harm in setting this value larger than your SGA requirements.

The parameters will be set by default on:

Oracle Linux with oracle-validated package (See Document 437743.1) installed.
Oracle Exadata DB compute nodes

Step 2: Re-logon to the Oracle product owner account (e.g. 'oracle') and check the memlock limit

$ ulimit -l
60397977

Step 3: If you have Oracle Database 11g or later, the default database created uses the Automatic Memory Management (AMM) feature which is incompatible with HugePages. Disable AMM before proceeding. To disable, set the initialization parameters MEMORY_TARGET and MEMORY_MAX_TARGET to 0 (zero). Please see Document 749851.1 for further information in case you encounter the error below:

ORA-00845: MEMORY_TARGET not supported on this system

Note: Starting in 11.2.0.3, AMM is no longer configured by default if DBCA detects that the machine has more than 4GB of RAM. See Document 1453227.1 for details.

Step 4: Make sure that all your database instances are up (including ASM instances) as they would run on production. Use the script hugepages_settings.sh in Document 401749.1 to calculate the recommended value for the vm.nr_hugepageskernel parameter. e.g.:

$ ./hugepages_settings.sh
...
Recommended setting: vm.nr_hugepages = 1496
$

Note: You can also calculate a proper value for the parameter yourself but that is not advised if you do not have extensive experience with HugePages and concepts.

Step 5: Edit the file /etc/sysctl.conf and set the vm.nr_hugepages parameter there:

...
vm.nr_hugepages = 1496
...

This will make the parameter to be set properly with each reboot.

Step 6: Stop all the database instances and reboot the server

(Although settings could have been done dynamically they would not be effective to the extent we require before a reboot. The best practice is to do a persistent system configuration and perform a reboot to complete the configuration as presented through the steps above)

What If the Database / SGA Configurations Change?

The performed configuration is basically based on the RAM installed and combined size of SGA of database instances you are running. Based on that when:

Amount of RAM installed for the Linux OS changed
New database instance(s) introduced
SGA size / configuration changed for one or more database instances

you should revise your HugePages configuration to make it suitable to the new memory framework. If not you may experience one or more problems below on the system:

Poor database performance
System running out of memory or excessive swapping
Database instances cannot be started
Crucial system services failing

三、检查确认Check and Validate the Configuration

After the system is rebooted, make sure that your database instances (including the ASM instances) are started. Automatic startup via OS configuration or CRS, or manual startup (whichever method you use) should have been performed. Check the HugePages state from /proc/meminfo. e.g.:

# grep HugePages /proc/meminfo
HugePages_Total:    1496
HugePages_Free:      485
HugePages_Rsvd:      446
HugePages_Surp:        0

The values in the output will vary. To make sure that the configuration is valid, the HugePages_Free value should be smaller than HugePages_Total and there should be some HugePages_Rsvd. HugePages_Rsvd counts free pages that are reserved for use (requested for an SGA, but not touched/mapped yet).

The sum of Hugepages_Free and HugePages_Rsvd may be smaller than your total combined SGA as instances allocate pages dynamically and proactively as needed.

四、计算大页Shell Script to Calculate Values Recommended Linux HugePages / HugeTLB Configuration

1.[root@wang ~]# vi hugepages_settings.sh
--添加如下脚本

#!/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
"hugepages_settings.sh" [New] 94L, 3254C written
[root@wang ~]#

2.[root@wang ~]# chmod +x hugepages_settings.sh

3.[root@wang ~]# ./hugepages_settings.sh
.........................
省略..............
Press Enter to proceed...

Recommended setting: vm.nr_hugepages = 102404

执行后会有输出建议值。

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linux配置大页HugePages

三、检查确认Check and Validate the Configuration

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