關於Linux系統的HugePages與Oracle資料庫優化，可以參考熊爺之前的文章，相關概念介紹的非常清晰：

• Linux大記憶體頁Oracle資料庫優化

本文旨在Linux系統上快速配置HugePages：

• 1.設定memlock無限制
• 2.設定合理的vm.nr_hugepages
• 3.確認HugePages設定成功

測試環境：RHEL6.8 + 512G實體記憶體；Oracle 11.2.0.4 SGA=400G.

1.設定memlock無限制

在/etc/security/limits.conf配置檔案中，設定oracle使用者memlock無限制：
vi /etc/security/limits.conf

oracle soft memlock unlimited
oracle hard memlock unlimited

2.設定合理的vm.nr_hugepages

在/etc/sysctl.conf配置檔案中，設定合理的vm.nr_hugepages值。
執行MOS 401749.1提供的hugepages_settings.sh指令碼，直接可以得到建議值。
hugepages_settings.sh指令碼內容：

#!/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
 

直接執行指令碼即可得到對應的建議：

--當啟動的例項設定SGA_MAX_SIZE=12G，給出建議：
Recommended setting: vm.nr_hugepages = 6148

--當啟動的例項設定SGA_MAX_SIZE=400G，給出建議：
Recommended setting: vm.nr_hugepages = 204805

--當沒有啟動例項時，會報錯提示：
***********
** ERROR **
***********
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
 

我這裡將建議值vm.nr_hugepages = 204805追加到/etc/sysctl.conf配置檔案中，然後執行sysctl -p生效配置。

3.確認HugePages設定成功

檢視關於HugePages的資訊，注意HugePages_Total值是之前設定的204805：
grep Huge /proc/meminfo

# grep Huge /proc/meminfo 
AnonHugePages:         0 kB
HugePages_Total:   204805
HugePages_Free:    168475
HugePages_Rsvd:    168471
HugePages_Surp:        0
Hugepagesize:       2048 kB

資料庫在啟動時，對應alert日誌中會有“Large Pages Information”內容：

Wed Nov 14 14:38:12 2018
Starting ORACLE instance (normal)
************************ Large Pages Information *******************
Per process system memlock (soft) limit = UNLIMITED
 
Total Shared Global Region in Large Pages = 400 GB (100%)
 
Large Pages used by this instance: 204801 (400 GB)
Large Pages unused system wide = 4 (8192 KB)
Large Pages configured system wide = 204805 (400 GB)
Large Page size = 2048 KB
********************************************************************

至此可以確認HugePages設定成功。