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    SubjectRe: [RFC][PATCH 1/2] memcg: res_counter hierarchy
    KAMEZAWA Hiroyuki wrote:
    > This patch tries to implements _simple_ 'hierarchy policy' in res_counter.
    >
    > While several policy of hierarchy can be considered, this patch implements
    > simple one
    > - the parent includes, over-commits the child
    > - there are no shared resource

    I am not sure if this is desirable. The concept of a hierarchy applies really
    well when there are shared resources.

    > - dynamic hierarchy resource usage management in the kernel is not necessary
    >

    Could you please elaborate as to why? I am not sure I understand your point

    > works as following.
    >
    > 1. create a child. set default child limits to be 0.
    > 2. set limit to child.
    > 2-a. before setting limit to child, prepare enough room in parent.
    > 2-b. increase 'usage' of parent by child's limit.

    The problem with this is that you are forcing the parent will run into a reclaim
    loop even if the child is not using the assigned limit to it.

    > 3. the child sets its limit to the val moved from the parent.
    > the parent remembers what amount of resource is to the children.
    >

    All of this needs to be dynamic

    > Above means that
    > - a directory's usage implies the sum of all sub directories +
    > own usage.
    > - there are no shared resource between parent <-> child.
    >
    > Pros.
    > - simple and easy policy.
    > - no hierarchy overhead.
    > - no resource share among child <-> parent. very suitable for multilevel
    > resource isolation.

    Sharing is an important aspect of hierachies. I am not convinced of this
    approach. Did you look at the patches I sent out? Was there something
    fundamentally broken in them?

    [snip]

    --
    Warm Regards,
    Balbir Singh
    Linux Technology Center
    IBM, ISTL


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