Transparent HugePages内存在Red Hat企业Linux 6,SUSE 11和Oracle Linux 6的Oracle Linux Unbreakable Enterprise Kernel2(UEK2)早期版本中默认是启用的。Transparent HugePages内存在Oracle Linux Unbreakable Enterprise Kernel2(UEK2)内核中默认情况下是禁用的。”tuned.service”在Oracle Linux7中默认是将transparent_hugepage设置为always。即使在grub内核命令行中它是禁用的，在boot时tuned service将被设置为’always’。在UEK3中默认情况下是禁用的。

Transparent HugePages可能会造成内存在运行时的延迟分配。为了避免性能问题，Oracle强烈建议对所有Oracle数据库服务器禁用Transparent HugePages。

为了提高性能Oracle建议使用标准HugePages。

Transparent HugePages内存与标准HugePages内存的差异在于内核khugepaged线程在运行时动态分配内存。标准HugePages内存是在启动时预先分配在运行时不会发生改变。

1.检查Transparent HugePage是否被启用

[root@oracle12c ~]# uname -r

3.10.0-123.el7.x86_64

[root@oracle12c ~]# cat /sys/kernel/mm/transparent_hugepage/enabled

[always] madvise never ---这说明Transparent Hugepage被启用

2.有两种禁用Transparent HugePage的模式

2.1对吞吐性能方面全局禁用Transparent HugePage

先对文件/usr/lib/tuned/throughput-performance/tuned.conf进行备份

[root@oracle12c ~]# ls -lrt /usr/lib/tuned/throughput-performance/tuned.conf*

-rw-r--r--. 1 root root 2050 May 7 2014 /usr/lib/tuned/throughput-performance/tuned.conf

-rw-r--r--. 1 root root 2050 Mar 29 11:04 /usr/lib/tuned/throughput-performance/tuned.conf.bkp

[root@oracle12c ~]# more /usr/lib/tuned/throughput-performance/tuned.conf | grep "transparent_hugepages"

transparent_hugepages=always

修改文件/usr/lib/tuned/throughput-performance/tuned.conf，将其中的

[vm]

transparent_hugepages=always

修改为

[vm]

transparent_hugepages=never

[root@oracle12c ~]# more /usr/lib/tuned/throughput-performance/tuned.conf | grep "transparent_hugepages"

transparent_hugepages=never

重启操作系统来验证修改结果

[root@oracle12c ~]# uname -r

3.10.0-123.el7.x86_64

[root@oracle12c ~]# cat /sys/kernel/mm/transparent_hugepage/enabled

always madvise [never]

2.2.对正使用的调整概要文件禁用Transparent HugePage先识别正使用的调整概要文件

[root@oracle12c ~]# tuned-adm active

Current active profile: virtual-guest --这说明当前正使用的概要文件是Virtual-guest

Virtual-guest profile是使用文件/usr/lib/tuned/virtual-guest/tuned.conf，

并且它包含了来自文件/usr/lib/tuned/throughput-performance/tuned.conf中的”throughput-performance”。首先对文件/usr/lib/tuned/virtual-guest/tuned.conf进行备份

[root@oracle12c ~]# cp /usr/lib/tuned/virtual-guest/tuned.conf /usr/lib/tuned/virtual-guest/tuned.conf.bkp

[root@oracle12c ~]# ls -lrt /usr/lib/tuned/virtual-guest/tuned.conf*

-rw-r--r--. 1 root root 697 Nov 6 2013 /usr/lib/tuned/virtual-guest/tuned.conf

-rw-r--r--. 1 root root 697 Mar 29 11:26 /usr/lib/tuned/virtual-guest/tuned.conf.bkp

[root@oracle12c ~]# more /usr/lib/tuned/virtual-guest/tuned.conf

#

# tuned configuration

#

[main]

include=throughput-performance

[sysctl]

# If a workload mostly uses anonymous memory and it hits this limit, the entire

# working set is buffered for I/O, and any more write buffering would require

# swapping, so it's time to throttle writes until I/O can catch up. Workloads

# that mostly use file mappings may be able to use even higher values.

#

# The generator of dirty data starts writeback at this percentage (system default

# is 20%)

vm.dirty_ratio = 30

# Filesystem I/O is usually much more efficient than swapping, so try to keep

# swapping low. It's usually safe to go even lower than this on systems with

# server-grade storage.

vm.swappiness = 30

向文件/usr/lib/tuned/virtual-guest/tuned.conf中增加”transparent_hugepages=never”来禁用Transparent HugePage

[root@oracle12c ~]# vi /usr/lib/tuned/virtual-guest/tuned.conf

#

# tuned configuration

#

[main]

include=throughput-performance

[vm]

transparent_hugepages=never

[sysctl]

# If a workload mostly uses anonymous memory and it hits this limit, the entire

# working set is buffered for I/O, and any more write buffering would require

# swapping, so it's time to throttle writes until I/O can catch up. Workloads

# that mostly use file mappings may be able to use even higher values.

#

# The generator of dirty data starts writeback at this percentage (system default

# is 20%)

vm.dirty_ratio = 30

# Filesystem I/O is usually much more efficient than swapping, so try to keep

# swapping low. It's usually safe to go even lower than this on systems with

# server-grade storage.

vm.swappiness = 30

重启操作系统来验证结果

[root@oracle12c ~]# uname -r

3.10.0-123.el7.x86_64

[root@oracle12c ~]# cat /sys/kernel/mm/transparent_hugepage/enabled

always madvise [never]