Btrfs: Scale the bdi ra_pages by the number of devices in the FS

Signed-off-by: NChris Mason <chris.mason@oracle.com>

fs/btrfs/disk-io.c

@@ -932,7 +932,7 @@ static int setup_bdi(struct btrfs_fs_info *info, struct backing_dev_info *bdi)
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,23)
 	bdi_init(bdi);
 #endif
-	bdi->ra_pages	= default_backing_dev_info.ra_pages * 4;
+	bdi->ra_pages	= default_backing_dev_info.ra_pages;
 	bdi->state		= 0;
 	bdi->capabilities	= default_backing_dev_info.capabilities;
 	bdi->unplug_io_fn	= btrfs_unplug_io_fn;
@@ -1214,6 +1214,8 @@ struct btrfs_root *open_ctree(struct super_block *sb,
 		       (unsigned long long)fs_devices->num_devices);
 		goto fail_sb_buffer;
 	}
+	fs_info->bdi.ra_pages *= btrfs_super_num_devices(disk_super);
+
 	nodesize = btrfs_super_nodesize(disk_super);
 	leafsize = btrfs_super_leafsize(disk_super);
 	sectorsize = btrfs_super_sectorsize(disk_super);