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    SubjectRe: [RFC][PATCH 6/6] automatic tuning applied to some kernel components
    Date
    Nadia Derbey <Nadia.Derbey@bull.net> writes:

    >
    > 2) why autotuning:
    > There are at least 3 cases where it can be useful
    > . for workloads that are known to need a big amount of a given resource type
    > (say shared memories), but we don't know what the maximum amount needed will be
    > . to solve the case of multiple applications running on a single system, and
    > that need the same tunable to be adjusted to feet their needs
    > . to make a system correctly react to eventual peak loads for a given resource
    > usage, i.e. make it tune up *and down* as needed.

    >
    > In all these cases, the akt framework will enable the kernel to adapt to
    > increasing / decreasing resource consumption:
    > 1) avoid allocating "a priori" a big amount of memory that will be used only in
    > extreme cases. This is the effect of doing an "echo <huge_value>
    >> /proc/sys/kernel/shmmni"
    >
    > 2) the system will come back to the default values as soon as the peak load is
    > over.

    At least the ipc ones are supposed to be DOS limits not behavior
    modifiers. I do admit from looking at the code that there are some
    consequences of increasing things like shmmni. However I think we
    would be better off with better data structures and implementations
    that remove these consequences than this autotuning of
    denial-of-service limits.

    i.e. I think you are treating the symptom not the problem.

    Does this make sense?

    Eric

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