Linux kernel is the core of many popular operating systems such as Ubuntu, SuSE, RedHat and so on. Its memory management is an important part of the kernel and has a profound influence on the stability and performance of these operating systems. In this article, I will explore the memory management of the Linux kernel in depth.

Memory management in Linux is essentially divided into two parts: physical memory management and virtual memory management. Physical memory management allocates and manages RAM, flash memory, and other memory areas. Its key function is to spread the load of application processes in physical memory areas and make efficient use of the available resources. Virtual memory management allocates and manages the address space of the application process provided by the kernel. Its main tasks include the allocation and recovery of memory, memory protection, etc.

The basic concepts of Linux kernel memory management include physical address, virtual address, kernel virtual address and user virtual address. Physical address is the memory location in physical RAM. Virtual address is the memory address provided by the kernel, and users can also access this address in their own address space. Kernel virtual address is a special area for the kernel and only the kernel can access it. User virtual address is the area where applications run, which is only accessible by user processes.

In Linux, memory pages are the basic unit of memory management. A page is a block of 4KB (or 2MB in some cases) of RAM. The kernel divides the physical memory into pages and each page has an associated page table entry, which is used to record whether the page is being used, how it is used, etc.

Linux kernel memory management also uses two page-mapping data structures: page table and page directory. The page table is used to store the physical and virtual address mapping, while the page directory contains information about the characteristics of each page, such as whether it is effectively used or not, etc. With the help of these data structures, the kernel can quickly locate and access any page.

In addition, Linux provides various memory management mechanisms, such as memory fragmentation and virtual memory. Memory fragmentation is an optimization technique used to reduce wasted memory; it works by reclaiming unused memory and combining free memory blocks into a large block. Virtual memory, on the other hand, enables processes to have their own virtual address space, providing the same benefits as memory fragmentation but with less overhead.

In conclusion, the memory management of the Linux kernel is a complex but essential system. It includes many components, such as physical memory management, virtual memory management, page tables and page directory. By using these components, the kernel can easily and efficiently manage the RAM, flash memory and other memory areas. In addition, it also provides various memory optimization and management mechanisms to maximize the performance of the operating system.