The readahead code searches the page cache for non-present pages, or
holes, to get a picture of the area surrounding a fault e.g.
For this it sufficed to rely on the radix tree definition of holes,
which is "empty tree slot". This is about to change, though, because
shadow page descriptors will be stored in the page cache when the real
pages get evicted from memory.
Fortunately, nobody outside the readahead code uses these functions
and they have no internal knowledge of the radix tree structures, so
just move them over to mm/readahead.c where they can later be adapted
to handle the new definition of "page cache hole".
Signed-off-by: Johannes Weiner<hannes@xxxxxxxxxxx>