Deep understanding of Linux caching mechanism: key steps to optimize system performance

Mastering the Linux caching mechanism: a key step to improve system performance, specific code examples are required

Abstract: The caching mechanism of the Linux system is one of the important factors in improving system performance . This article will introduce the caching mechanism of Linux, focusing on page caching and disk caching, and give specific code examples to help readers better understand and apply the Linux caching mechanism to improve system performance.

1. Introduction
With the development of computer technology, modern operating systems face the challenge of performance bottlenecks when processing large amounts of data. In order to improve the operating efficiency of the system, the Linux system introduces a caching mechanism to cache data on the disk in the memory, thereby reducing the number of disk IOs and improving system performance. This article will delve into the caching mechanism of Linux and use specific code examples to help readers understand and apply the Linux caching mechanism.

2. Linux caching mechanism

1. Page caching
   Page caching is the most common form of caching in Linux. When files are read into memory, they are stored in the page cache. In subsequent read operations, the kernel first checks the page cache. If it finds that the page of the file has been cached, it reads directly from the page cache, avoiding disk IO operations. Page caching is useful for files that are frequently read (such as system files, library files, etc.).
2. Disk cache
   In addition to page caching, Linux also introduces a disk caching mechanism to cache data on the disk in memory. When an application needs to write data to the disk, the kernel first writes the data to the disk cache, and writes the data in the cache to the disk at the appropriate time, reducing the number of disk IOs and improving system performance. Disk caching is very beneficial for applications that frequently write to disk, such as databases.

3. Specific code examples
The following are some specific code examples to show how to use the Linux caching mechanism to improve system performance.

1. Use the mmap function for memory mapping of files

   #include <fcntl.h>
   #include <sys/mman.h>
   #include <sys/stat.h>
   #include <unistd.h>
   
   int main() {
    int fd = open("test.txt", O_RDONLY);
    struct stat sb;
    fstat(fd, &sb);
   
    void* addr = mmap(NULL, sb.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
    // 现在test.txt文件的内容被映射到了内存中的addr处，可以直接从内存中读取数据
   
    munmap(addr, sb.st_size);
    close(fd);
    return 0;
   }

   By using the mmap function, the file "test.txt" is mapped to the memory and can be read directly from the memory Fetching the contents of the file avoids disk IO operations and improves system performance.

2. Use the write function to write data

   #include <fcntl.h>
   #include <unistd.h>
   
   int main() {
    int fd = open("test.txt", O_WRONLY | O_CREAT, 0644);
    const char* buf = "Hello, World!
   ";
    size_t len = strlen(buf);
   
    write(fd, buf, len);
    // 现在数据被写入到磁盘缓存中，稍后会由内核将数据写入磁盘
   
    close(fd);
    return 0;
   }

   By using the write function, write the data to the disk cache of the file "test.txt", later Data is written to disk by the kernel. This can reduce frequent disk IO operations and improve system performance.

4. Summary
This article introduces the caching mechanism of Linux, focusing on page caching and disk caching, and gives specific code examples. By properly applying the caching mechanism, frequent disk IO operations can be avoided and system performance improved. Readers can flexibly apply the caching mechanism according to specific needs and application scenarios to improve system performance.

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