On Wed, May 26, 2021 at 1:12 PM Yang Shi [off-list ref] wrote:

Currently try_to_unmap() return bool value by checking page_mapcount(),
however this may return false positive since page_mapcount() doesn't
check all subpages of compound page.  The total_mapcount() could be used
instead, but its cost is higher since it traverses all subpages.

Actually the most callers of try_to_unmap() don't care about the
return value at all.  So just need check if page is still mapped by
page_mapped() when necessary.  And page_mapped() does bail out early
when it finds mapped subpage.

Suggested-by: Hugh Dickins <hughd@google.com>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Yang Shi <redacted>

Reviewed-by: Shakeel Butt <redacted>