Comment by addaon

> I suspect the intent is to move stale things out of RAM so it can be immediately used for more productive purposes when needed.

These are separate problems, though. You can clean a page by updating its backing store without purging it from memory; and purging a clean page doesn’t require a write. It’s definitely reasonable to take advantage of idle IO resources to clean dirty pages, but pages should only be purged (clean pages first, usually) when there’s an immediate need for them for something else.