Linux kernel memory management (ZONE_DMA zone_normal zone_highmem Introduction) __linux

CPU is divided into nodes, memory is clustered, each CPU corresponds to a local physical memory, that is, a cpu-node corresponding to a memory cluster bank, that is, each memory cluster is considered a node. The physical memory of the system is divided into several nodes, and a node corresponds to a memory cluster bank, where each memory cluster is considered to be one.

First, the memory is divided into nodes, each node is associated to a processor in the system, and the kernel is represented as an instance of pg_data_t. Each node in the system is linked to a null-terminated pgdat_list List < Each node is linked to the next node > using the Pg_data_tnode_next field. But for the PC this UMA structure machine, only uses one is called the Contig_page_data static pg_data_t structure. In today's 32-bit computers with large capacity RAM, the CPU cannot directly access all physical addresses, because the linear address space is too small for the kernel to directly map all physical memory to the linear address space.