backing_dev_info.ra_pages0 is a user configurable parameter that controls
the readahead size on start-of-file.

Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
Signed-off-by: Andrew Morton <akpm@osdl.org>
--- linux-2.6.19-rc5-mm2.orig/block/ll_rw_blk.c
+++ linux-2.6.19-rc5-mm2/block/ll_rw_blk.c
@@ -3795,6 +3795,24 @@ queue_ra_store(struct request_queue *q, 
 	return ret;
 }
 
+static ssize_t queue_initial_ra_show(struct request_queue *q, char *page)
+{
+	int kb = q->backing_dev_info.ra_pages0 << (PAGE_CACHE_SHIFT - 10);
+
+	return queue_var_show(kb, (page));
+}
+
+static ssize_t
+queue_initial_ra_store(struct request_queue *q, const char *page, size_t count)
+{
+	unsigned long kb;
+	ssize_t ret = queue_var_store(&kb, page, count);
+
+	q->backing_dev_info.ra_pages0 = kb >> (PAGE_CACHE_SHIFT - 10);
+
+	return ret;
+}
+
 static ssize_t queue_max_sectors_show(struct request_queue *q, char *page)
 {
 	int max_sectors_kb = q->max_sectors >> 1;
@@ -3852,6 +3870,12 @@ static struct queue_sysfs_entry queue_ra
 	.store = queue_ra_store,
 };
 
+static struct queue_sysfs_entry queue_initial_ra_entry = {
+	.attr = {.name = "initial_ra_kb", .mode = S_IRUGO | S_IWUSR },
+	.show = queue_initial_ra_show,
+	.store = queue_initial_ra_store,
+};
+
 static struct queue_sysfs_entry queue_max_sectors_entry = {
 	.attr = {.name = "max_sectors_kb", .mode = S_IRUGO | S_IWUSR },
 	.show = queue_max_sectors_show,
@@ -3872,6 +3896,7 @@ static struct queue_sysfs_entry queue_io
 static struct attribute *default_attrs[] = {
 	&queue_requests_entry.attr,
 	&queue_ra_entry.attr,
+	&queue_initial_ra_entry.attr,
 	&queue_max_hw_sectors_entry.attr,
 	&queue_max_sectors_entry.attr,
 	&queue_iosched_entry.attr,

--
-
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