mm: swap-token: add a comment for priority aging

Document some swap token aging design decisions.

Signed-off-by: KOSAKI Motohiro <[email protected]>
Acked-by: Rik van Riel <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
1 file changed