mm/filemap: fix readahead return types

A readahead request will not allocate more memory than can be represented
by a size_t, even on systems that have HIGHMEM available. Change the
length functions from returning an loff_t to a size_t.

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: 32c0a6bcaa1f57 ("btrfs: add and use readahead_batch_length")
Signed-off-by: Matthew Wilcox (Oracle) <[e-mail]>
Reviewed-by: Darrick J. Wong <[e-mail]>
Reported-by: Linus Torvalds <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/iomap/buffered-io.c

···
 {
 	struct inode *inode = rac->mapping->host;
 	loff_t pos = readahead_pos(rac);
-	loff_t length = readahead_length(rac);
+	size_t length = readahead_length(rac);
 	struct iomap_readpage_ctx ctx = {
 		.rac	= rac,
 	};
···
 	trace_iomap_readahead(inode, readahead_count(rac));
 
 	while (length > 0) {
-		loff_t ret = iomap_apply(inode, pos, length, 0, ops,
+		ssize_t ret = iomap_apply(inode, pos, length, 0, ops,
 				&ctx, iomap_readahead_actor);
 		if (ret <= 0) {
 			WARN_ON_ONCE(ret == 0);

include/linux/pagemap.h

···
  * readahead_length - The number of bytes in this readahead request.
  * @rac: The readahead request.
  */
-static inline loff_t readahead_length(struct readahead_control *rac)
+static inline size_t readahead_length(struct readahead_control *rac)
 {
-	return (loff_t)rac->_nr_pages * PAGE_SIZE;
+	return rac->_nr_pages * PAGE_SIZE;
 }
 
 /**
···
  * readahead_batch_length - The number of bytes in the current batch.
  * @rac: The readahead request.
  */
-static inline loff_t readahead_batch_length(struct readahead_control *rac)
+static inline size_t readahead_batch_length(struct readahead_control *rac)
 {
 	return rac->_batch_count * PAGE_SIZE;
 }