The virtual memory parameters are listed in the /proc/sys/vm directory.

The following are the available virtual memory parameters:

vm.dirty_ratio

A percentage value. When this percentage of total system memory is modified, the system begins writing the modifications to the disk. The default value is 20 percent.

vm.dirty_background_ratio

A percentage value. When this percentage of total system memory is modified, the system begins writing the modifications to the disk in the background. The default value is 10 percent.

vm.overcommit_memory

Defines the conditions that determine whether a large memory request is accepted or denied. The default value is 0. The kernel grants memory requests based on total available RAM and swap, rejecting only large allocations. Otherwise, virtual memory allocations are granted, and can allow memory overcommitment.

Setting the overcommit_memory parameter’s value

• When set to 1, the kernel performs no memory overcommit handling. This increases the possibility of memory overload, but improves performance for memory-intensive tasks.
• When set to 2, the kernel denies allocations exceeding the total swap plus the RAM percentage defined in overcommit_ratio. This setting reduces the risk of overcommitting memory. Use this only for systems with the swap partition larger than physical memory.

vm.overcommit_ratio

Specifies the percentage of physical RAM considered when overcommit_memory is set to 2. The default value is 50.

vm.max_map_count

Defines the maximum number of memory map areas that a process can use. The default value is 65530. Increase this value if your application needs more memory map areas.

vm.min_free_kbytes

Sets the size of the reserved free pages pool. It is also responsible for setting the min_page, low_page, and high_page thresholds. These thresholds govern the behavior of the page reclaim algorithms in the Linux kernel. It also specifies to keep the minimum number of free kilobytes across the system. This calculates a specific value for each low memory zone. Each zone is assigned a number of reserved free pages in proportion to its size.

Setting the vm.min_free_kbytes parameter’s value

• Increasing the parameter value effectively reduces the application working set usable memory. Therefore, you can use it for only kernel-driven workloads, where driver buffers need to be allocated in atomic contexts.
• Decreasing the parameter value might render the kernel unable to service system requests if memory becomes heavily contended in the system. Warning
  Extreme values can be detrimental to the system’s performance. Setting the vm.min_free_kbytes to an extremely low value prevents the system from reclaiming memory effectively. This can result in system crashes and failure to service interrupts or other kernel services. However, setting vm.min_free_kbytes too high considerably increases system reclaim activity, causing allocation latency due to a false direct reclaim state. This might cause the system to immediately enter an out-of-memory state. The vm.min_free_kbytes parameter also sets a page reclaim watermark, called min_pages. This watermark is used as a factor when determining the two other memory watermarks, low_pages, and high_pages, that govern page reclaim algorithms.
• /proc/PID/oom_adj In the event, when a system runs out of memory and the panic_on_oom parameter is set to 0, the oom_killer function kills processes, starting with the process that has the highest oom_score, until the system recovers. The oom_adj parameter determines the oom_score of a process. This parameter is set per process identifier. A value of -17 disables the oom_killer for that process. Other valid values range from -16 to 15. Note
  Processes created by an adjusted process inherit the oom_score of that process.

vm.swappiness

The swappiness value, ranging from 0 to 200, controls whether the system prioritizes reclaiming memory from anonymous pages or the page cache.

Setting the swappiness parameter’s value

• Higher values prefer file-mapped driven workloads while swapping out the less actively accessed processes’ anonymous mapped memory of RAM. File servers and streaming applications use this to keep data in memory, reducing I/O latency.
• Low values prefer anonymous-mapped driven workloads while reclaiming the page cache (file mapped memory). This setting is useful for applications that do not depend heavily on file system information and use dynamically allocated private memory. Examples include mathematical and number-crunching applications and some hardware virtualization supervisors such as QEMU. The default value of the vm.swappiness parameter is 60. Warning
  Setting the vm.swappiness to 0 aggressively avoids swapping out anonymous memory to a disk. This increases the likelihood that the oom_killer function kills processes during memory or I/O-intensive workloads.