linux配置大内存技术

1、理论介绍

  
系统进程通过虚拟地址访问内存，CPU必须把它转换成物理内存地址才能真正访问内存。为了提高这个转换效率,CPU会缓存最近的虚拟内存地址和物理内存地址的映射关系，并保存在一个

由CPU维护的映射表中。为了尽量提高内存的访问速度，需要在映射表中保存尽量多的映射关系。在linux系统中,所有内存都是以页的形式划分的，默认情况下每页是4096B，这就意味着如果

物理内存很大，映射表的条目数会很多，系统cpu在检索的过程中，需要检索的条目数就会很。从另一个角度说，如果能够让cpu减少检索内存条目的数量，可采取的办法只有增加页的尺寸，

hugepage应时而生。hugepage，一直被cache,不会被交换出去,也就是说使用hugepage的内存不能被其他的进程使用。随着内存技术的发展，现在上T的内存配置也出现，所以内存已经不是问

题，在实际应用中，如果你的物理内存能够达到8g以上，那么都可以使用大内存技术。在oracle数据库中，sga与大内存配合使用，将会对性能产生非常大的提升。

2、oracle中大内存技术的配置建议

   oracle针对大内存技术，提供了一个脚本如下：
#!/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 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}'`
 
#
Initialize the counter
NUM_PG=0
 
# Cumulative number of pages required
to handle the running shared memory segments
for SEG_BYTES in `ipcs -m | awk
'{print $5}' | grep "[0-9][0-9]*"`
do
   MIN_PG=`echo
"$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

[root@hdyydb1 u02]# chmod u+x hugepages_settings.sh
[root@hdyydb1 u02]#
./hugepages_settings.sh

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 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...

Recommended setting: vm.nr_hugepages = 2588

可以看到，运行脚本显示，将vm.nr_hugepages设置为2588

3、hugepage在oracle中的配置应用

--检查系统是否启用hugepage，或者是否可以启用
[root@hdyydb1 u02]# cat /proc/meminfo | grep
-i huge
AnonHugePages:     75776 kB
HugePages_Total:      
0
HugePages_Free:        0
HugePages_Rsvd:       
0
HugePages_Surp:        0
Hugepagesize:       2048 kB

可以看到，HugePages_Total,HugePages_Free均为零，证明没有使用，但可以配置。如果上面什么都没有显示，证明不能配置。

--检查数据库的参数设置是否支持
SQL> show parameter sga_target

NAME                                 TYPE       
VALUE
------------------------------------ -----------
------------------------------
sga_target                           big
integer 0

大内存技术，不支持内存自动管理，必须关闭AMM(自动内存管理）特性才能使用hugepage

调整方法如下：

ALTER SYSTEM SET sga_max_size = xxxxM SCOPE=SPFILE;
ALTER SYSTEM SET
sga_target = xxxxM SCOPE=SPFILE;
ALTER SYSTEM SET PGA_AGGREGATE_TARGET =
xxxxM SCOPE=SPFILE;
ALTER SYSTEM SET memory_target = 0 SCOPE=SPFILE;
ALTER
SYSTEM SET memory_max_target = 0 SCOPE=SPFILE;

--根据第二步的验证结果进行配置

[root@hdyydb1 u02]# vi /etc/sysctl.conf
把vm.nr_hugepages = 2588 添加进去，并保存

[root@hdyydb1 u02]# sysctl -p
net.ipv4.ip_forward =
0
net.ipv4.conf.default.rp_filter =
1
net.ipv4.conf.default.accept_source_route = 0
kernel.sysrq =
0
kernel.core_uses_pid = 1
net.ipv4.tcp_syncookies =
1
net.bridge.bridge-nf-call-ip6tables =
0
net.bridge.bridge-nf-call-iptables =
0
net.bridge.bridge-nf-call-arptables = 0
kernel.msgmnb =
65536
kernel.msgmax = 65536
fs.aio-max-nr = 1048576
fs.file-max =
6815744
kernel.shmall = 2097152
kernel.shmmax =
7247757312
kernel.shmmni = 4096
kernel.sem = 250 32000 100
128
net.ipv4.ip_local_port_range = 9000 65500
net.core.rmem_default =
262144
net.core.rmem_max = 4194304
net.core.wmem_default =
262144
net.core.wmem_max = 1048586
vm.min_free_kbytes =
51200
vm.nr_hugepages = 2588

检查设置：
[root@hdyydb1 u02]# cat /proc/meminfo | grep -i
huge
AnonHugePages:     75776 kB
HugePages_Total:    
977
HugePages_Free:      977
HugePages_Rsvd:       
0
HugePages_Surp:        0
Hugepagesize:       2048 kB

--锁定内存配置
如果不配置锁定内存，在后alert_sid.log中会有类似如下的建议：
RECOMMENDATION:
 
Total System Global Area size is 5 GB. For optimal performance,
  prior to
the next instance restart:
  1. Large pages are automatically locked into
physical memory.
 Increase the per process memlock (soft) limit to at least 5
GB to lock
 100% System Global Area's large pages into physical
memory
并且，hugepage并没有真正使用起来！

主要是配置
oracle soft memlock
oracle hard memlock
实际物理内存 > 锁定内存
>=HugePages_Total*Hugepagesize

[root@hdyydb1 u02]# vim /etc/security/limits.conf
添加：
oracle soft
memlock 6291456
oracle hard memlock 6291456

我的物理内存是8g，sga 5g左右

4、重启操作系统、数据库后生效

[oracle@hdyydb1 ~]$ cat /proc/meminfo | grep -i huge
AnonHugePages:    
43008 kB
HugePages_Total:    2588
HugePages_Free:    
2168
HugePages_Rsvd:     2165
HugePages_Surp:       
0
Hugepagesize:       2048 kB

free比total小，证明已经生效