btrfs: readpages() should submit IO as read-ahead

a_ops->readpages() is only ever used for read-ahead.  Ensure that we
pass this information down to the block layer.

Link: http://lkml.kernel.org/r/20180621010725.17813-4-axboe@kernel.dk
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Chris Mason <clm@fb.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 628f1aef34b0c409a76c5abf4820b2fbdef2d72b..4dd6faab02bb5b58ef321003a76a6d2594fb7234 100644 (file)
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3102,7 +3102,7 @@ static inline void __do_contiguous_readpages(struct extent_io_tree *tree,
 
        for (index = 0; index < nr_pages; index++) {
                __do_readpage(tree, pages[index], btrfs_get_extent, em_cached,
-                               bio, 0, bio_flags, 0, prev_em_start);
+                               bio, 0, bio_flags, REQ_RAHEAD, prev_em_start);
                put_page(pages[index]);
        }
 }