How does the memory swapping function work?

Swapping is a memory management mechanism that allows the operating system to move inactive memory pages from RAM to a hard disk (or another storage device called a swap partition or file). This frees up space in RAM for more actively used data and processes. When data from the swap partition is needed again, it is returned to RAM.

How it works:

Identifying inactive pages: The operating system monitors memory page usage. Inactive or rarely used pages are marked as candidates for unloading.
Unloading (Swap Out): Selected pages are copied from RAM to the swap partition on the disk. After successful copying, these pages are freed in RAM.
Swapping in (Swap In): When a process accesses data that was unloaded to swap, the operating system generates a page fault.
Reading from swap: The operating system finds the required page in the swap partition and loads it back into RAM. It may need to unload another inactive page to free space.
Resuming execution: Once the page is loaded, the process can continue execution.

Advantages of swapping:

Allows running more applications than can fit in RAM.
Prevents application crashes due to insufficient memory.

Disadvantages of swapping:

Swapping is significantly slower than RAM access because it involves disk operations (which are much slower).
Excessive swapping (thrashing) can lead to severe system slowdown, as most of the time is spent on input/output operations for swapping.

Configuring and monitoring swap is important for system performance. In Linux, for example, swappiness controls how aggressively the kernel unloads pages:

# View current swappiness value
cat /proc/sys/vm/swappiness

# Change swappiness value (temporary)
sudo sysctl vm.swappiness=10 
# A lower value (closer to 0) makes the kernel try to keep pages in RAM
# A higher value (closer to 100) makes the kernel unload pages more aggressively

Using the free command allows viewing the current memory state, including swap:

# View memory information including swap
free -h