io-controller: Document for blkio.weight_device

Here is the document for blkio.weight_device

Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

diff --git a/Documentation/cgroups/blkio-controller.txt b/Documentation/cgroups/blkio-controller.txt
index db054ea3e7fbb1d2a88fd48b8bb59a46b47c8c17..d422b410a995908c1d5c5439963b64253c1b6ffd 100644 (file)
--- a/Documentation/cgroups/blkio-controller.txt
+++ b/Documentation/cgroups/blkio-controller.txt
@@ -76,9 +76,38 @@ CONFIG_DEBUG_BLK_CGROUP
 Details of cgroup files
 =======================
 - blkio.weight
-       - Specifies per cgroup weight.
+       - Specifies per cgroup weight. This is default weight of the group
+         on all the devices until and unless overridden by per device rule.
+         (See blkio.weight_device).
          Currently allowed range of weights is from 100 to 1000.
 
+- blkio.weight_device
+       - One can specify per cgroup per device rules using this interface.
+         These rules override the default value of group weight as specified
+         by blkio.weight.
+
+         Following is the format.
+
+         #echo dev_maj:dev_minor weight > /path/to/cgroup/blkio.weight_device
+         Configure weight=300 on /dev/sdb (8:16) in this cgroup
+         # echo 8:16 300 > blkio.weight_device
+         # cat blkio.weight_device
+         dev     weight
+         8:16    300
+
+         Configure weight=500 on /dev/sda (8:0) in this cgroup
+         # echo 8:0 500 > blkio.weight_device
+         # cat blkio.weight_device
+         dev     weight
+         8:0     500
+         8:16    300
+
+         Remove specific weight for /dev/sda in this cgroup
+         # echo 8:0 0 > blkio.weight_device
+         # cat blkio.weight_device
+         dev     weight
+         8:16    300
+
 - blkio.time
        - disk time allocated to cgroup per device in milliseconds. First
          two fields specify the major and minor number of the device and