Step-by-Step HugePages Configuration (Oracle 19c on Linux)

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🔹 Step 1: Check Current HugePages Status

grep Huge /proc/meminfo

Key parameters:

• HugePages_Total
• HugePages_Free
• Hugepagesize (usually 2 MB)

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🔹 Step 2: Disable Transparent HugePages (THP)

Oracle recommends disabling THP.

Check status:

cat /sys/kernel/mm/transparent_hugepage/enabled

Disable temporarily:

echo never > /sys/kernel/mm/transparent_hugepage/enabled

echo never > /sys/kernel/mm/transparent_hugepage/defrag

Disable permanently:

Edit:

vi /etc/default/grub

Add:

transparent_hugepage=never

Then apply:

grub2-mkconfig -o /boot/grub2/grub.cfg

reboot

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🔹 Step 3: Calculate Required HugePages

3.1 Check Oracle SGA size

From SQL:

show parameter sga_target;

or:

show parameter memory_target;

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3.2 Use Oracle Script (Recommended)

$ORACLE_HOME/bin/hugepages_settings.sh

If not available, download from Oracle MOS.

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3.3 Manual Calculation

Formula:

HugePages = Total_SGA_Size / HugePage_Size

Example:

• SGA = 64 GB
• Page size = 2 MB

64 * 1024 MB / 2 MB = 32768 HugePages

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🔹 Step 4: Configure HugePages in Kernel

Edit:

vi /etc/sysctl.conf

Add/update:

vm.nr_hugepages=32768

Apply:

sysctl -p

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🔹 Step 5: Configure memlock for Oracle User

Edit:

vi /etc/security/limits.conf

Add:

oracle soft memlock 67108864

oracle hard memlock 67108864

👉 Value should match SGA size (in KB)

Example:

64 GB = 67108864 KB

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🔹 Step 6: Disable AMM (Very Important)

HugePages does NOT work with AMM.

Check:

show parameter memory_target;

If > 0, disable:

ALTER SYSTEM SET memory_target=0 SCOPE=SPFILE;

ALTER SYSTEM SET memory_max_target=0 SCOPE=SPFILE;

Instead, use ASMM:

ALTER SYSTEM SET sga_target=64G SCOPE=SPFILE;

ALTER SYSTEM SET pga_aggregate_target=8G SCOPE=SPFILE;

Restart DB:

shutdown immediate;

startup;

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🔹 Step 7: Restart Server

reboot

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🔹 Step 8: Validate HugePages Usage

grep Huge /proc/meminfo

Check:

• HugePages_Total → should match configured value
• HugePages_Free → should decrease after DB start
• HugePages_Rsvd → reserved pages

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🔹 Step 9: Verify Oracle is Using HugePages

grep -i huge /proc/meminfo

Also check alert log:

grep HugePages $ORACLE_BASE/diag/rdbms/*/*/trace/alert*.log

Expected message:

Huge Pages allocation successful

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✅ Best Practices

✔ Always leave some RAM for OS (not 100% HugePages)
✔ Use static SGA (ASMM)
✔ Set HugePages slightly higher than requirement
✔ Monitor with:

vmstat

free -g

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⚠️ Common Mistakes

❌ Using AMM (memory_target)
❌ Not setting memlock
❌ THP not disabled
❌ Underestimating number of HugePages

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🚀 Quick Example Summary

For a 64 GB SGA:

Setting	Value
HugePage size	2 MB
Required pages	32768
memlock	67108864 KB
vm.nr_hugepages	32768

Oracle Script for huge_page setting 

vi 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 KB151310 from My Oracle Support 

# http://support.oracle.com 

# Welcome text 

echo " 

This script is provided by KB151310 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 the overall 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 Automatic Memory Management (AMM) is not setup 

   (See KB83222) 

 * 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 Automatic Memory Management (AMM) is not configured" 

    exit 1 

fi 

# Finish with results 

    echo "Recommended setting: vm.nr_hugepages = $NUM_PG"; 

# End