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Dredging up my knowledge from OS class, there are three sections of memory for a (Von Neumann architecture) program: the data section (also called the program section), the stack, and the heap.

The data section is the actual compiled bits of the program: the machine instructions themselves. The stack and heap are memory used by the program at run-time.

Completely separate from that, on a Linux system, there is the VFS buffer-cache system. When you write to a "file", you are actually writing to VFS buffer cache memory, and the OS then flushes that dirty page of VFS cache to disk, at which point the write is committed.

Your description of page-outs sounds as though you are describing the operation of the VFS buffer cache flushing its dirty pages to disk.

In my college education (1998 to 2003), we used the terms swap-out and page-out interchangeably.

However, I have heard some people make the distinction of using page-outs/ins to specifically refer to just the data section of an app being written to / read from disk, with term swap-outs/ins referring to the same operation on the stack and heap.

But I've never encountered the term "page-outs" being used to refer to dirty file-backed storage pages being flushed to disk. Is this an old-school hacker thing? Or did I misunderstand and create a straw man?




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