Chapter2.docx
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Chapter2.Describing Physical
Memory
Linux is available for a wide range of architectures, so an architecture-independent
way of describing memory is needed. This chapter describes the structures used to
keep account of memory banks, pages and ags that aect VM behavior.
Linux 可用于多种体系结构，因此需要一种与体系结构无关的内存描述方式。 本章介绍用于保留影
响虚拟机行为的内存库，页面和标志的结构。
The "rst principal concept prevalent in the VM is Non Uniform Memory Access (NUMA).
With large-scale machines, memory may be arranged into banks that incur a dierent
cost to access depending on their distance from the processor. For example, a bank of
memory might be assigned to each CPU, or a bank of memory very suitable for Direct
Memory Access (DMA) near device cards might be assigned.
VM 中流行的第一个主要概念是非统一内存访问（NUMA）。 对于大型机器，可能会将内存排列到
存储体中，这取决于它们与处理器之间的距离而导致不同的访问成本。 例如，可以为每个 CPU 分
配一组内存，或者可以为非常靠近设备卡的直接内存访问（DMA）分配一组内存。
Each bank is called a node, and the concept is represented under Linux by a struct
pglist_data even if the architecture is Uniform Memory Access (UMA). This struct is
always referenced by its typedef pg_data_t. Every node in the system is kept on a
NULL terminated list called pgdat_list, and each node is linked to the next with the
"eld pg_data_t→node_next. For UMA architectures like PC desktops, only one static
pg_data_t structure called contig_page_data is used. Nodes are discussed further in
Section 2.1.
每个存储体都称为一个节点，并且在 Linux 下，即使体系结构是统一内存访问（UMA），该概念也
由 pglist_data 结构表示。 该结构始终由其 typedef pg_data_t 引用。 系统中的每个节点都保存
在一个名为 pgdat_list 的 NULL 终止列表中，并且每个节点都通过字段 pg_data_t→node_next
链接到下一个节点。 对于 PC 台式机等 UMA 体系结构，仅使用一种称为 contig_page_data 的静
态 pg_data_t 结构。 在第 2.1 节中将进一步讨论节点。
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