mm: rmap: make try_to_unmap() void function

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.

Link: https://lkml.kernel.org/r/[email protected]
Suggested-by: Hugh Dickins <[email protected]>
Signed-off-by: Yang Shi <[email protected]>
Acked-by: Minchan Kim <[email protected]>
Reviewed-by: Shakeel Butt <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]>
Signed-off-by: Hugh Dickins <[email protected]>
Acked-by: Naoya Horiguchi <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Jue Wang <[email protected]>
Cc: "Matthew Wilcox (Oracle)" <[email protected]>
Cc: Miaohe Lin <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Ralph Campbell <[email protected]>
Cc: Wang Yugui <[email protected]>
Cc: Zi Yan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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