From: Wu Fengguang <wfg@mail.ustc.edu.cn>

Backward prefetching is vital to structural analysis and some other
scientific applications.  Comment this use case.

Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 mm/readahead.c |    2 ++
 1 file changed, 2 insertions(+)

diff -puN mm/readahead.c~readahead-backward-prefetching-method-add-use-case-comment mm/readahead.c
--- a/mm/readahead.c~readahead-backward-prefetching-method-add-use-case-comment
+++ a/mm/readahead.c
@@ -1550,6 +1550,8 @@ initial_readahead(struct address_space *
  * Backward prefetching.
  *
  * No look-ahead and thrashing safety guard: should be unnecessary.
+ *
+ * Important for certain scientific arenas(i.e. structural analysis).
  */
 static int
 try_read_backward(struct file_ra_state *ra, pgoff_t begin_index,
_