swappiness

Swappiness is a Linux kernel parameter that controls how aggressively the kernel uses swap space to free up memory. It is part of the virtual memory management subsystem and is exposed as the integer value vm.swappiness, in the range 0 to 100. The default value on many distributions is 60, though this can vary.

The kernel uses swappiness to balance memory between anonymous memory (process data) and the page cache. A lower value makes the kernel prefer reclaiming file-backed cache and keep more anonymous memory in RAM, delaying swapping. A higher value makes the kernel swap out anonymous pages sooner to keep more free memory for new allocations, at the cost of potential swap I/O and latency when swapped pages are accessed again.

Viewing and adjusting swappiness can be done at runtime. You can check the current setting with cat /proc/sys/vm/swappiness. To change it temporarily, use sudo sysctl -w vm.swappiness=VALUE or echo VALUE | sudo tee /proc/sys/vm/swappiness. To make the change permanent, place a line such as vm.swappiness=VALUE in a sysctl configuration file (for example /etc/sysctl.d/99-swappiness.conf) and reload the settings.

When to tune swappiness: a lower value (for example 10–20) is often recommended for desktop systems or workloads with fast storage, as it reduces swap-related latency and keeps more data in RAM. A higher value (60–80) can be suitable for servers with large RAM pools and slower storage, where delaying swap could lead to higher memory pressure and thrashing. Swappiness does not disable swapping; under heavy memory pressure the kernel may still swap.