Add kernel-doc and return the number of pages removed in order to
get the statistics right in __invalidate_mapping_pages().
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NMiaohe Lin <linmiaohe@huawei.com>