mm: don't waste swap on locked pages

mm: don't waste swap on locked pages

try_to_unmap always fails on a page found in a VM_LOCKED vma (unless
migrating), and recycles it back to the active list.  But if it's an
anonymous page, we've already allocated swap to it: just wasting swap.
Spot locked pages in page_referenced_one and treat them as referenced.

Signed-off-by: Hugh Dickins <[email protected]>
Tested-by: KAMEZAWA Hiroyuki <[email protected]>
Cc: Ethan Solomita <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>