===================================================================
@@ -16,3 +16,5 @@ memory.txt
- Memory Resource Controller; design, accounting, interface, testing.
resource_counter.txt
- Resource Counter API.
+blkio.txt
+ - Block I/O Tracking; description, interface and examples.
===================================================================
@@ -0,0 +1,49 @@
+Block I/O Cgroup
+
+1. Overview
+
+Using this feature the owners of any type of I/O can be determined.
+This allows dm-ioband to control block I/O bandwidth even when it is
+accepting delayed write requests. dm-ioband can find the cgroup of
+each request. It is also for possible that others working on I/O
+bandwidth throttling to use this functionality to control asynchronous
+I/O with a little enhancement.
+
+2. Setting up blkio-cgroup
+
+The following kernel config options are required.
+
+CONFIG_CGROUPS=y
+CONFIG_CGROUP_BLKIO=y
+
+Selecting the options for the cgroup memory subsystem is also recommended
+as it makes it possible to give some I/O bandwidth and memory to a selected
+cgroup to control delayed write requests. The amount of dirty pages is
+limited within the cgroup even if the allocated bandwidth is narrow.
+
+CONFIG_RESOURCE_COUNTERS=y
+CONFIG_CGROUP_MEM_RES_CTLR=y
+
+3. User interface
+
+3.1 Mounting the cgroup filesystem
+
+First, mount the cgroup filesystem in order to enable observation and
+modification of the blkio-cgroup settings.
+
+# mount -t cgroup -o blkio none /cgroup
+
+3.2 The blkio.id file
+
+After mounting the cgroup filesystem the blkio.id file will be visible
+in the cgroup directory. This file contains a unique ID number for
+each cgroup. When an I/O operation starts, blkio-cgroup sets the
+page's ID number on the page cgroup. The cgroup of I/O can be
+determined by retrieving the ID number from the page cgroup, because
+the page cgroup is associated with the page which is involved in the
+I/O.
+
+4. Contact
+
+Linux Block I/O Bandwidth Control Project
+http://sourceforge.net/projects/ioband/