内核文档链接：https://www.kernel.org/doc/html/latest/admin-guide/sysctl/vm.html

内核文档对drop_caches的解释：

Writing to this will cause the kernel to drop clean caches, as well as reclaimable slab objects like dentries and inodes. Once dropped, their memory becomes free.

释放页面缓存（pagecache）

# echo 1 > /proc/sys/vm/drop_caches

或

# sudo sysctl -w vm.drop_caches=1

释放文件的数据结构和目录的数据结构（分别指inode 和 dentries）

# echo 2 > /proc/sys/vm/drop_caches

或

# sudo sysctl -w vm.drop_caches=2

释放文件数据结构、目录数据结构和页面缓存

# echo 3 > /proc/sys/vm/drop_caches

或

# sudo sysctl -w vm.drop_caches=3

其它参考链接：

https://unix.stackexchange.com/questions/87908/how-do-you-empty-the-buffers-and-cache-on-a-linux-system

https://stackoverflow.com/questions/29870068/what-are-pagecache-dentries-inodes

https://www.linuxatemyram.com/