readahead: data structure and routines

Extend struct file_ra_state to support the on-demand readahead logic.  Also
define some helpers for it.

Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
Cc: Steven Pratt <slpratt@austin.ibm.com>
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 19 insertions, 0 deletions

diff --git a/mm/readahead.c b/mm/readahead.c
index 7f9bf588c936..072ce8f8357d 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -592,3 +592,22 @@ unsigned long max_sane_readahead(unsigned long nr)
         return min(nr, (node_page_state(numa_node_id(), NR_INACTIVE)
                 + node_page_state(numa_node_id(), NR_FREE_PAGES)) / 2);
 }
+
+/*
+ * Submit IO for the read-ahead request in file_ra_state.
+ */
+unsigned long ra_submit(struct file_ra_state *ra,
+                       struct address_space *mapping, struct file *filp)
+{
+        unsigned long ra_size;
+        unsigned long la_size;
+        int actual;
+
+        ra_size = ra_readahead_size(ra);
+        la_size = ra_lookahead_size(ra);
+        actual = __do_page_cache_readahead(mapping, filp,
+                                        ra->ra_index, ra_size, la_size);
+
+        return actual;
+}
+EXPORT_SYMBOL_GPL(ra_submit);