1.透明大页介绍
Transparent Huge Pages的一些官方介绍资料:
2.查看是否启用透明大页
(1).使用命令查看时,如果输出结果为[always]表示透明大页启用了。[never]表示透明大页禁用、[madvise]表示(只在MADV_HUGEPAGE标志的VMA中使用THP
(2).如何HugePages_Total返回0,也意味着标准大页禁用了(注意传统/标准大页和透明大页的区别)
透明大页(THP)管理和标准/传统大页(HP)管理都是操作系统为了减少页表转换消耗的资源而发布的新特性,虽然ORACLE建议利用大页机制来提高数据库的性能,但是ORACLE却同时建议关闭透明大页管理。这二者的区别在于大页的分配机制,标准大页管理是预分配的方式,而透明大页管理则是动态分配的方式。
(3).cat /proc/sys/vm/nr_hugepages返回0也意味着传统大页禁用了(传统大页和透明大页)
3.禁用、启用透明大页功能(2).永久关闭
(1).临时禁用
(2).永久关闭
在/etc/rc.d/rc.local中增加以下内容
vim /etc/rc.d/rc.local
4.小知识点
(1).从RedHat 6, OEL 6, SLES 11 and UEK2 kernels 开始,系统缺省会启用 Transparent HugePages :用来提高内存管理的性能透明大页(Transparent HugePages )和之前版本中的大页功能上类似。主要的区别是:Transparent HugePages 可以实时配置,不需要重启才能生效配置;
(2).Transparent Huge Pages在32位的RHEL 6中是不支持的。
Transparent Huge Pages are not available on the 32-bit version of RHEL 6.
(3).ORACLE官方不建议我们使用RedHat 6, OEL 6, SLES 11 and UEK2 kernels 时的开启透明大页(Transparent HugePages ), 因为透明大页(Transparent HugePages ) 存在一些问题:
Transparent HugePages memory is enabled by default with Red Hat Enterprise Linux 6, SUSE Linux Enterprise Server 11, and Oracle Linux 6 with earlier releases of Oracle Linux Unbreakable Enterprise Kernel 2 (UEK2) kernels. Transparent HugePages memory is disabled in later releases of Oracle Linux UEK2 kernels.Transparent HugePages can cause memory allocation delays during runtime. To avoid performance issues, Oracle recommends that you disable Transparent HugePages on all Oracle Database servers. Oracle recommends that you instead use standard HugePages for enhanced performance.Transparent HugePages memory differs from standard HugePages memory because the kernel khugepaged thread allocates memory dynamically during runtime. Standard HugePages memory is pre-allocated at startup, and does not change during runtime.
Starting with RedHat 6, OEL 6, SLES 11 and UEK2 kernels, Transparent HugePages are implemented and enabled (default) in an attempt to improve the memory management. Transparent HugePages are similar to the HugePages that have been available in previous Linux releases. The main difference is that the Transparent HugePages are set up dynamically at run time by the khugepaged thread in kernel while the regular HugePages had to be preallocated at the boot up time. Because Transparent HugePages are known to cause unexpected node reboots and performance problems with RAC, Oracle strongly advises to disable the use of Transparent HugePages. In addition, Transparent Hugepages may cause problems even in a single-instance database environment with unexpected performance problems or delays. As such, Oracle recommends disabling Transparent HugePages on all Database servers running Oracle.
(4).安装Vertica Analytic Database时也必须关闭透明大页功能。
原文链接:https://www.cnblogs.com/kerrycode/p/4670931.html