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    Subject[PATCH 8/8] blkio-cgroup: Document for blkio.use_hierarchy.
    Document for blkio.use_hierarchy.

    Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
    ---
    Documentation/cgroups/blkio-controller.txt | 58 +++++++++++++++++++---------
    1 files changed, 39 insertions(+), 19 deletions(-)

    diff --git a/Documentation/cgroups/blkio-controller.txt b/Documentation/cgroups/blkio-controller.txt
    index 4ed7b5c..9c6dc9e 100644
    --- a/Documentation/cgroups/blkio-controller.txt
    +++ b/Documentation/cgroups/blkio-controller.txt
    @@ -91,30 +91,44 @@ Throttling/Upper Limit policy

    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.
    +- Cgroup interface allows creation of hierarchical cgroups. Currently,
    + internally IO policies are able to treat them as flat hierarchy or
    + hierarchical hierarchy. Both hierarchical bandwidth division and flat
    + bandwidth division are supported. "blkio.use_hierarchy" can be used to
    + switch between flat mode and hierarchical mode.

    - 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.
    + Consider the following CGroup hierarchy:

    - root
    - / \
    - test1 test2
    - |
    - test3
    + Root
    + / | \
    + Grp1 Grp2 tsk1
    + / \
    + Grp3 tsk2

    - CFQ and throttling will practically treat all groups at same level.
    + If flat mode is enabled, CFQ and throttling will practically treat all
    + groups at the same level.

    - pivot
    - / | \ \
    - root test1 test2 test3
    + Pivot tree
    + / | | \
    + Root Grp1 Grp2 Grp3
    + / |
    + tsk1 tsk2

    - 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.
    + If hierarchical mode is enabled, CFQ will treat groups and tasks as the same
    + view in CGroup hierarchy.
    +
    + Root
    + / | \
    + Grp1 Grp2 tsk1
    + / \
    + Grp3 tsk2
    +
    + Grp1, Grp2 and tsk1 are treated at the same level under Root group. Grp3 and
    + tsk2 are treated at the same level under Grp1. Below is the mapping between
    + task io priority and io weight:
    +
    + prio 0 1 2 3 4 5 6 7
    + weight 1000 868 740 612 484 356 228 100

    Various user visible config options
    ===================================
    @@ -169,6 +183,12 @@ Proportional weight policy files
    dev weight
    8:16 300

    +- blkio.use_hierarchy
    + - Switch between hierarchical mode and flat mode as stated above.
    + blkio.use_hierarchy == 1 means hierarchical mode is enabled.
    + blkio.use_hierarchy == 0 means flat mode is enabled.
    + The default mode is flat mode.
    +
    - blkio.time
    - disk time allocated to cgroup per device in milliseconds. First
    two fields specify the major and minor number of the device and
    --
    1.6.5.2



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