Merge tag 'v2.6.38' of git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6

[mv-sheeva.git] / Documentation / cgroups / blkio-controller.txt

diff --git a/Documentation/cgroups/blkio-controller.txt b/Documentation/cgroups/blkio-controller.txt
index d6da611f8f6338c66cf59e9b8df21eeaa4df500d..4ed7b5ceeed212c1b7a734451456896f4759ee9d 100644 (file)
--- a/Documentation/cgroups/blkio-controller.txt
+++ b/Documentation/cgroups/blkio-controller.txt
@@ -89,6 +89,33 @@ Throttling/Upper Limit policy
 
  Limits for writes can be put using blkio.write_bps_device file.
 
+Hierarchical Cgroups
+====================
+- Currently none of the IO control policy supports hierarhical groups. But
+  cgroup interface does allow creation of hierarhical cgroups and internally
+  IO policies treat them as flat hierarchy.
+
+  So this patch will allow creation of cgroup hierarhcy but at the backend
+  everything will be treated as flat. So if somebody created a hierarchy like
+  as follows.
+
+                       root
+                       /  \
+                    test1 test2
+                       |
+                    test3
+
+  CFQ and throttling will practically treat all groups at same level.
+
+                               pivot
+                            /  |   \  \
+                       root  test1 test2  test3
+
+  Down the line we can implement hierarchical accounting/control support
+  and also introduce a new cgroup file "use_hierarchy" which will control
+  whether cgroup hierarchy is viewed as flat or hierarchical by the policy..
+  This is how memory controller also has implemented the things.
+
 Various user visible config options
 ===================================
 CONFIG_BLK_CGROUP