Here is the document of dm-ioband.

Based on 2.6.26-rc5-mm3
Signed-off-by: Ryo Tsuruta <ryov@valinux.co.jp>
Signed-off-by: Hirokazu Takahashi <taka@valinux.co.jp>

diff -uprN linux-2.6.26-rc5-mm3.orig/Documentation/device-mapper/ioband.txt linux-2.6.26-rc5-mm3/Documentation/device-mapper/ioband.txt
--- linux-2.6.26-rc5-mm3.orig/Documentation/device-mapper/ioband.txt	1970-01-01 09:00:00.000000000 +0900
+++ linux-2.6.26-rc5-mm3/Documentation/device-mapper/ioband.txt	2008-07-04 12:21:10.000000000 +0900
@@ -0,0 +1,933 @@
+                     Block I/O bandwidth control: dm-ioband
+
+            -------------------------------------------------------
+
+   Table of Contents
+
+   [1]What's dm-ioband all about?
+
+   [2]Differences from the CFQ I/O scheduler
+
+   [3]How dm-ioband works.
+
+   [4]Setup and Installation
+
+   [5]Getting started
+
+   [6]Command Reference
+
+   [7]Examples
+
+What's dm-ioband all about?
+
+     dm-ioband is an I/O bandwidth controller implemented as a device-mapper
+   driver. Several jobs using the same physical device have to share the
+   bandwidth of the device. dm-ioband gives bandwidth to each job according
+   to its weight, which each job can set its own value to.
+
+     At this time, a job is a group of processes with the same pid or pgrp or
+   uid. There is also a plan to make it support cgroup. A job can also be a
+   virtual machine such as KVM or Xen.
+
+     +------+ +------+ +------+   +------+ +------+ +------+
+     |cgroup| |cgroup| | the  |   | pid  | | pid  | | the  |  jobs
+     |  A   | |  B   | |others|   |  X   | |  Y   | |others|
+     +--|---+ +--|---+ +--|---+   +--|---+ +--|---+ +--|---+
+     +--V----+---V---+----V---+   +--V----+---V---+----V---+
+     | group | group | default|   | group | group | default|  ioband groups
+     |       |       |  group |   |       |       |  group |
+     +-------+-------+--------+   +-------+-------+--------+
+     |        ioband1         |   |       ioband2          |  ioband devices
+     +-----------|------------+   +-----------|------------+
+     +-----------V--------------+-------------V------------+
+     |                          |                          |
+     |          sdb1            |           sdb2           |  physical devices
+     +--------------------------+--------------------------+
+
+
+   --------------------------------------------------------------------------
+
+Differences from the CFQ I/O scheduler
+
+     Dm-ioband is flexible to configure the bandwidth settings.
+
+     Dm-ioband can work with any type of I/O scheduler such as the NOOP
+   scheduler, which is often chosen for high-end storages, since it is
+   implemented outside the I/O scheduling layer. It allows both of partition
+   based bandwidth control and job --- a group of processes --- based
+   control. In addition, it can set different configuration on each physical
+   device to control its bandwidth.
+
+     Meanwhile the current implementation of the CFQ scheduler has 8 IO
+   priority levels and all jobs whose processes have the same IO priority
+   share the bandwidth assigned to this level between them. And IO priority
+   is an attribute of a process so that it equally effects to all block
+   devices.
+
+   --------------------------------------------------------------------------
+
+How dm-ioband works.
+
+     Every ioband device has one ioband group, which by default is called the
+   default group.
+
+     Ioband devices can also have extra ioband groups in them. Each ioband
+   group has a job to support and a weight. Proportional to the weight,
+   dm-ioband gives tokens to the group.
+
+     A group passes on I/O requests that its job issues to the underlying
+   layer so long as it has tokens left, while requests are blocked if there
+   aren't any tokens left in the group. Tokens are refilled once all of
+   groups that have requests on a given physical device use up their tokens.
+
+     There are two policies for token consumption. One is that a token is
+   consumed for each I/O request. The other is that a token is consumed for
+   each I/O sector, for example, one I/O request which consists of
+   4Kbytes(512bytes * 8 sectors) read consumes 8 tokens. A user can choose
+   either policy.
+
+     With this approach, a job running on an ioband group with large weight
+   is guaranteed a wide I/O bandwidth.
+
+   --------------------------------------------------------------------------
+
+Setup and Installation
+
+     Build a kernel with these options enabled:
+
+     CONFIG_MD
+     CONFIG_BLK_DEV_DM
+     CONFIG_DM_IOBAND
+
+
+     If compiled as module, use modprobe to load dm-ioband.
+
+     # make modules
+     # make modules_install
+     # depmod -a
+     # modprobe dm-ioband
+
+
+     "dmsetup targets" command shows all available device-mapper targets.
+   "ioband" is displayed if dm-ioband has been loaded.
+
+     # dmsetup targets
+     ioband           v1.2.0
+
+
+   --------------------------------------------------------------------------
+
+Getting started
+
+     The following is a brief description how to control the I/O bandwidth of
+   disks. In this description, we'll take one disk with two partitions as an
+   example target.
+
+   --------------------------------------------------------------------------
+
+  Create and map ioband devices
+
+     Create two ioband devices "ioband1" and "ioband2". "ioband1" is mapped
+   to "/dev/sda1" and has a weight of 40. "ioband2" is mapped to "/dev/sda2"
+   and has a weight of 10. "ioband1" can use 80% --- 40/(40+10)*100 --- of
+   the bandwidth of the physical disk "/dev/sda" while "ioband2" can use 20%.
+
+    # echo "0 $(blockdev --getsize /dev/sda1) ioband /dev/sda1 1 0 0 none" \
+        "weight 0 :40" | dmsetup create ioband1
+    # echo "0 $(blockdev --getsize /dev/sda2) ioband /dev/sda2 1 0 0 none" \
+        "weight 0 :10" | dmsetup create ioband2
+
+
+     If the commands are successful then the device files
+   "/dev/mapper/ioband1" and "/dev/mapper/ioband2" will have been created.
+
+   --------------------------------------------------------------------------
+
+  Additional bandwidth control
+
+     In this example two extra ioband groups are created on "ioband1". The
+   first group consists of all the processes with user-id 1000 and the second
+   group consists of all the processes with user-id 2000. Their weights are
+   30 and 20 respectively.
+
+    # dmsetup message ioband1 0 type user
+    # dmsetup message ioband1 0 attach 1000
+    # dmsetup message ioband1 0 attach 2000
+    # dmsetup message ioband1 0 weight 1000:30
+    # dmsetup message ioband1 0 weight 2000:20
+
+
+     Now the processes in the user-id 1000 group can use 30% ---
+   30/(30+20+40+10)*100 --- of the bandwidth of the physical disk.
+
+   Table 1. Weight assignments
+
+   +----------------------------------------------------------------+
+   | ioband device |          ioband group          | ioband weight |
+   |---------------+--------------------------------+---------------|
+   | ioband1       | user id 1000                   | 30            |
+   |---------------+--------------------------------+---------------|
+   | ioband1       | user id 2000                   | 20            |
+   |---------------+--------------------------------+---------------|
+   | ioband1       | default group(the other users) | 40            |
+   |---------------+--------------------------------+---------------|
+   | ioband2       | default group                  | 10            |
+   +----------------------------------------------------------------+
+
+   --------------------------------------------------------------------------
+
+  Remove the ioband devices
+
+     Remove the ioband devices when no longer used.
+
+     # dmsetup remove ioband1
+     # dmsetup remove ioband2
+
+
+   --------------------------------------------------------------------------
+
+Command Reference
+
+  Create an ioband device
+
+   SYNOPSIS
+
+           dmsetup create IOBAND_DEVICE
+
+   DESCRIPTION
+
+             Create an ioband device with the given name IOBAND_DEVICE.
+           Generally, dmsetup reads a table from standard input. Each line of
+           the table specifies a single target and is of the form:
+
+             start_sector num_sectors "ioband" device_file ioband_device_id \
+                 io_throttle io_limit ioband_group_type policy token_base \
+                 :weight [ioband_group_id:weight...]
+
+
+                start_sector, num_sectors
+
+                          The sector range of the underlying device where
+                        dm-ioband maps.
+
+                ioband
+
+                          Specify the string "ioband" as a target type.
+
+                device_file
+
+                          Underlying device name.
+
+                ioband_device_id
+
+                          The ID number for an ioband device. The same ID
+                        must be set among the ioband devices that share the
+                        same bandwidth, which means they work on the same
+                        physical disk.
+
+                io_throttle
+
+                          Dm-ioband starts to control the bandwidth when the
+                        number of BIOs in progress exceeds this value. If 0
+                        is specified, dm-ioband uses the default value.
+
+                io_limit
+
+                          Dm-ioband blocks all I/O requests for the
+                        IOBAND_DEVICE when the number of BIOs in progress
+                        exceeds this value. If 0 is specified, dm-ioband uses
+                        the default value.
+
+                ioband_group_type
+
+