What is an anonymous page and how is it related to swap?

An anonymous memory page is a page in a process's virtual address space that is not associated with any specific file on disk. It is memory allocated by the process for its own needs, such as storing variable data or the stack. It holds information about the process's state, not data from a file.

The operating system uses an anonymous page as temporary storage for process data. When physical memory is insufficient, such pages can be swapped out to the disk's swap space. This frees up physical memory for other processes. When needed, data from the disk is swapped back into physical memory.

Relation to swap:

• Storage: Anonymous pages are primary candidates for swapping out because they do not have a permanent source on disk, unlike pages associated with files (e.g., executable code).
• Restoration: When an anonymous page is loaded back into physical memory, the OS must read it from the swap space.

# Example command to view memory information, including anonymous pages
# 'AnonPages' shows the number of anonymous pages
# 'SwapCached' shows the number of anonymous pages swapped out and cached in memory
cat /proc/meminfo