Hierarchical Cgroups
====================
-- Currently none of the IO control policy supports hierarchical groups. But
- cgroup interface does allow creation of hierarchical cgroups and internally
- IO policies treat them as flat hierarchy.
+- Currently only CFQ supports hierarchical groups. For throttling,
+ cgroup interface does allow creation of hierarchical cgroups and
+ internally it treats them as flat hierarchy.
- So this patch will allow creation of cgroup hierarchcy but at the backend
- everything will be treated as flat. So if somebody created a hierarchy like
- as follows.
+ If somebody created a hierarchy like as follows.
root
/ \
|
test3
- CFQ and throttling will practically treat all groups at same level.
+ CFQ will handle the hierarchy correctly but and throttling will
+ practically treat all groups at same level. For details on CFQ
+ hierarchy support, refer to Documentation/block/cfq-iosched.txt.
+ Throttling will treat the hierarchy as if it looks like the
+ following.
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.
+ Nesting cgroups, while allowed, isn't officially supported and blkio
+ genereates warning when cgroups nest. Once throttling implements
+ hierarchy support, hierarchy will be supported and the warning will
+ be removed.
Various user visible config options
===================================
dev weight
8:16 300
+- blkio.leaf_weight[_device]
+ - Equivalents of blkio.weight[_device] for the purpose of
+ deciding how much weight tasks in the given cgroup has while
+ competing with the cgroup's child cgroups. For details,
+ please refer to Documentation/block/cfq-iosched.txt.
+
- blkio.time
- disk time allocated to cgroup per device in milliseconds. First
two fields specify the major and minor number of the device and
and minor number of the device and third field specifies the number
of times a group was dequeued from a particular device.
+- blkio.*_recursive
+ - Recursive version of various stats. These files show the
+ same information as their non-recursive counterparts but
+ include stats from all the descendant cgroups.
+
Throttling/Upper limit policy files
-----------------------------------
- blkio.throttle.read_bps_device