Drivers shouldn't really mess with the readahead size, as that is a VM
concept.  Instead set it based on the optimal I/O size by lifting the
algorithm from the md driver when registering the disk.  Also set
bdi->io_pages there as well by applying the same scheme based on
max_sectors.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-settings.c         |  5 ++---
 block/blk-sysfs.c            | 10 +++++++++-
 block/genhd.c                |  5 +++--
 drivers/block/aoe/aoeblk.c   |  2 --
 drivers/block/drbd/drbd_nl.c | 12 +-----------
 drivers/md/bcache/super.c    |  4 ----
 drivers/md/dm-table.c        |  3 ---
 drivers/md/raid0.c           | 16 ----------------
 drivers/md/raid10.c          | 24 +-----------------------
 drivers/md/raid5.c           | 13 +------------
 10 files changed, 17 insertions(+), 77 deletions(-)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 76a7e03bcd6cac..01049e9b998f1d 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c

@@ -452,6 +452,8 @@ EXPORT_SYMBOL(blk_limits_io_opt);
 void blk_queue_io_opt(struct request_queue *q, unsigned int opt)
 {
 	blk_limits_io_opt(&q->limits, opt);
+	q->backing_dev_info->ra_pages =
+		max(queue_io_opt(q) * 2 / PAGE_SIZE, VM_READAHEAD_PAGES);
 }
 EXPORT_SYMBOL(blk_queue_io_opt);
 

@@ -628,9 +630,6 @@ void disk_stack_limits(struct gendisk *disk, struct block_device *bdev,
 		printk(KERN_NOTICE "%s: Warning: Device %s is misaligned\n",
 		       top, bottom);
 	}
-
-	t->backing_dev_info->io_pages =
-		t->limits.max_sectors >> (PAGE_SHIFT - 9);
 }
 EXPORT_SYMBOL(disk_stack_limits);
 

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 81722cdcf0cb21..95eb35324e1a61 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c

@@ -245,7 +245,6 @@ queue_max_sectors_store(struct request_queue *q, const char *page, size_t count)
 
 	spin_lock_irq(&q->queue_lock);
 	q->limits.max_sectors = max_sectors_kb << 1;
-	q->backing_dev_info->io_pages = max_sectors_kb >> (PAGE_SHIFT - 10);
 	spin_unlock_irq(&q->queue_lock);

@@ -854,6 +853,15 @@ int blk_register_queue(struct gendisk *disk)
 		percpu_ref_switch_to_percpu(&q->q_usage_counter);
 	}
 
+	/*
+	 * For read-ahead of large files to be effective, we need to read ahead
+	 * at least twice the optimal I/O size.
+	 */
+	q->backing_dev_info->ra_pages =
+		max(queue_io_opt(q) * 2 / PAGE_SIZE, VM_READAHEAD_PAGES);
+	q->backing_dev_info->io_pages =
+		queue_max_sectors(q) >> (PAGE_SHIFT - 9);
+
 	ret = blk_trace_init_sysfs(dev);
 	if (ret)
 		return ret;

diff --git a/block/genhd.c b/block/genhd.c
index 081f1039d9367f..db311a14ddc71a 100644
--- a/block/genhd.c
+++ b/block/genhd.c

@@ -772,6 +772,7 @@ static void __device_add_disk(struct device *parent, struct gendisk *disk,
 			      const struct attribute_group **groups,
 			      bool register_queue)
 {
+	struct request_queue *q = disk->queue;
 	dev_t devt;
 	int retval;
 

@@ -782,7 +783,7 @@ static void __device_add_disk(struct device *parent, struct gendisk *disk,
 	 * registration.
 	 */
 	if (register_queue)
-		elevator_init_mq(disk->queue);
+		elevator_init_mq(q);
 
 	/* minors == 0 indicates to use ext devt from part0 and should
 	 * be accompanied with EXT_DEVT flag.  Make sure all

@@ -812,7 +813,7 @@ static void __device_add_disk(struct device *parent, struct gendisk *disk,
 		disk->flags |= GENHD_FL_SUPPRESS_PARTITION_INFO;
 		disk->flags |= GENHD_FL_NO_PART_SCAN;
 	} else {
-		struct backing_dev_info *bdi = disk->queue->backing_dev_info;
+		struct backing_dev_info *bdi = q->backing_dev_info;
 		struct device *dev = disk_to_dev(disk);
 		int ret;

diff --git a/drivers/block/aoe/aoeblk.c b/drivers/block/aoe/aoeblk.c
index 5ca7216e9e01f3..89b33b402b4e52 100644
--- a/drivers/block/aoe/aoeblk.c
+++ b/drivers/block/aoe/aoeblk.c

@@ -347,7 +347,6 @@ aoeblk_gdalloc(void *vp)
 	mempool_t *mp;
 	struct request_queue *q;
 	struct blk_mq_tag_set *set;
-	enum { KB = 1024, MB = KB * KB, READ_AHEAD = 2 * MB, };
 	ulong flags;
 	int late = 0;
 	int err;

@@ -407,7 +406,6 @@ aoeblk_gdalloc(void *vp)
 	WARN_ON(d->gd);
 	WARN_ON(d->flags & DEVFL_UP);
 	blk_queue_max_hw_sectors(q, BLK_DEF_MAX_SECTORS);
-	q->backing_dev_info->ra_pages = READ_AHEAD / PAGE_SIZE;
 	d->bufpool = mp;
 	d->blkq = gd->queue = q;
 	q->queuedata = d;

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 1bbdc410ee3c51..ff2101d56cd7f1 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c

@@ -1427,10 +1427,6 @@ static int cached_dev_init(struct cached_dev *dc, unsigned int block_size)
 	if (ret)
 		return ret;
 
-	dc->disk.disk->queue->backing_dev_info->ra_pages =
-		max(dc->disk.disk->queue->backing_dev_info->ra_pages,
-		    q->backing_dev_info->ra_pages);
-