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-rw-r--r--Documentation/cgroups/blkio-controller.txt27
1 files changed, 27 insertions, 0 deletions
diff --git a/Documentation/cgroups/blkio-controller.txt b/Documentation/cgroups/blkio-controller.txt
index d6da611f8f63..4ed7b5ceeed2 100644
--- 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