The Linux kernel includes a virtual memory (VM) subsystem that manages the allocation and deallocation of physical memory (RAM) among different processes and kernel functions. The VM subsystem can be tuned to optimize the use of memory and improve system performance.
There are several key parameters that you can adjust to tune the VM subsystem in Linux:
swappiness: The swappiness parameter determines how aggressively the kernel will swap inactive pages out of physical memory and into the swap space on disk. A higher value for swappiness means that the kernel is more likely to swap pages out of memory, while a lower value means that the kernel will try to keep more pages in memory.
dirty_ratio and dirty_background_ratio: These parameters control the amount of dirty (modified) pages in memory. When the ratio of dirty pages to total pages exceeds the dirty_ratio, the kernel will start writing dirty pages to disk to free up memory. The dirty_background_ratio determines the amount of dirty pages at which the kernel will start writing dirty pages to disk in the background.
vfs_cache_pressure: This parameter controls the balance between inode and dentry caches (used for storing file system metadata) and page caches (used for storing file data). A higher value for vfs_cache_pressure means that the kernel will prefer to reclaim inode and dentry caches over page caches, while a lower value means that the kernel will prefer to reclaim page caches.
To tune the VM subsystem, you can edit the relevant parameters in the /proc/sys/vm/ directory or add them to the /etc/sysctl.conf file. You can also use the sysctl command to modify these parameters dynamically. It is important to test any changes to the VM subsystem carefully, as they can have a significant impact on system performance.