When to Evict Pages (Cleaning Policy)
	• An OS process called the paging daemon – wakes periodically to inspect pool of frames – if insufficient # of free frames • Mark pages for eviction according to policy, set valid bit to zero • Schedule disk to write dirty pages – on page fault • If desired page is marked but still in memory, use it • Otherwise, replace first clean marked page in pool • Advantage • Writing out dirty pages is not in critical path to swapping in