Linux中设置HugePages

Linux中使用HugePages可以减少操作系统对page的维护，增加TLB(translation Lookaside Buffer)的命中率.
由于HugePages和Oracle 的AMM不兼容，所以在Oracle 11g中使用HugePages需要禁用AMM.
The AMM and HugePages are not compatible. One needs to disable AMM on 11g to be able to use HugePages.

关于Linux中HugePages的详细论述可参考：
HugePages on Linux: What It Is... and What It Is Not... [ID 361323.1]

1.检查Hugepagesize设置
$ grep Hugepagesize /proc/meminfo
在不同Linux Kernel中默认的Hugepagesize是不同的。

2.修改Hugepagesize
a).计算Hugepagesize的方法
vm.nr_hugepages = sga_max_size / Hugepagesize = 12GB/2048KB = 6144 (can be set slightly bigger than this figure)

b).修改/etc/sysctl.conf
# echo "vm.nr_hugepages=6146" >> /etc/sysctl.conf
c).使修改生效
# sysctl -p
d).检查设置是否生效
# grep HugePages_Total /proc/meminfo
参考[MOS]:Frequent Instance Eviction in 9i or Node Eviction in 10g/11g [ID 461662.1]

 

Linux中自动计算HugePages的脚本:
Shell Script to Calculate Values Recommended Linux HugePages / HugeTLB Configuration [ID 401749.1]

#!/bin/bash
#
# hugepages_settings.sh
#
# Linux bash script to compute values for the recommended HugePages/HugeTLB configuration
#
# 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. 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 $KERN in
    '2.4') HUGETLB_POOL=`echo "$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" ;;
     *) echo "Unrecognized kernel version $KERN. Exiting." ;;
esac

# End