Linux HugePages 配置 与 Oracle 性能关系说明

Linux HugePages 配置 与 Oracle 性能关系说明

一. HugePages 说明

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HugePages is afeature integrated into the Linux kernel with release 2.6. This featurebasically provides the alternative to the 4K page size (16Kfor IA64) providing bigger pages.

关于HugePages，有一些相关的专业术语，具体如下：

（1） Page Table: A page table is thedata structure of a virtual memory system in an operating system to store themapping between virtual addresses and physical addresses. This means that on avirtual memory system, the memory is accessed by first accessing a page tableand then accessing the actual memory location implicitly.

--Page Table 是操作系统上的虚拟内存系统的数据结构，其用来存储虚拟内存地址和物理内存地址之间的映射关系。这就意味着在虚拟内存系统上，，我们访问内存时，是先访问Page Table，然后根据Page Table 中的映射关系，隐式的转移到物理的内存位置。

（2） TLB: A Translation LookasideBuffer (TLB) is a buffer (or cache) in a CPU that contains parts ofthe page table. This is a fixed size buffer being used to do virtual addresstranslation faster.

--TLB(Translation Lookaside Buffer) 是CPU 中的一块buffer 或者cache，其大小的固定的， TLB中包含了部分Page Table，用来快速进行虚拟地址的转换。

（3） hugetlb: This is an entryin the TLB that points to a HugePage (a large/big page larger than regular 4Kand predefined in size). HugePages are implemented via hugetlb entries, i.e. wecan say that a HugePage is handled by a "hugetlb page entry". The'hugetlb" term is also (and mostly) used synonymously with a HugePage(See Note261889.1). In this document the term "HugePage" is going to beused but keep in mind that mostly "hugetlb" refers to the sameconcept.

--hugetlb 是TLB中的一个entry，其指向HugePage（大于4k或预定义的一个large page）。 HugePage 通过hugetlb entries来实现，我们也可以说HugePage 是hugetlb page entry的一个句柄。 在MOS 文档：Note 261889.1中，二者是几乎是相同的概念。

（4） hugetlbfs: This is a newin-memory filesystem like tmpfs and is presented by 2.6 kernel. Pages allocatedon hugetlbfs type filesystem are allocated in HugePages.

--hugetlbfs 是2.6内核中提出的一个新的in-memory filesystem，就像tmpfs一样。

WRONG: HugePages is a method to be able to use large SGA on 32-bit VLM systems

RIGHT: HugePages is a method to have larger pages where it is useful for working with very large memory. It is both useful in 32- and 64-bit configurations

WRONG: HugePages cannot be used without USE_INDIRECT_DATA_BUFFERS

RIGHT: HugePages can be used without indirect buffers. 64-bit systems does not need to use indirect buffers to have a large buffer cache for the RDBMS instance and HugePages can be used there too.

WRONG: hugetlbfs means hugetlb

RIGHT: hugetlbfs is a filesystem type **BUT** hugetlb is the mechanism employed in the back where hugetlb can be employed WITHOUT hugetlbfs

WRONG: hugetlbfs means hugepages

RIGHT: hugetlbfs is a filesystem type **BUT** HugePages is the mechanism employed in the back (synonymously with hugetlb) where HugePages can be employed WITHOUT hugetlbfs.