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    SubjectRe: [patch 2/2] cpusets: add interleave_over_allowed option
    David wrote:
    > I prefer Choice B because it does not force mempolicies to have any
    > dependence on cpusets with regard to what nodemask is passed.

    Yes, well said.

    > It would be very good to store the passed nodemask to set_mempolicy in
    > struct mempolicy,

    Yes - that's what I'm intending to do.

    > If the cpuset has fewer than four nodes, the behavior
    > should be undefined (probably implemented to just cycle the set of
    > mems_allowed until you reach the fourth entry).

    I do intend to implement it as you suggest. See the lib/bitmap.c
    routines bitmap_remap() and bitmap_bitremap(), and the nodemask
    wrappers for these, nodes_remap() and node_remap(). They will
    define the cycling, or I sometimes call it folding.

    I would have tended to make this folding a defined part of the API,
    though I will grant that the possibility of being lazy and forgetting
    to document it seems attractive (less to document ;).

    > That [running in a cpuset with fewer nodes than used in a memory policy
    > mask] is the result of constraining a task to a cpuset that obviously
    > wants access to more nodes -- it's a userspace mistake and abusing
    > cpusets so that the task does not get what it expects.

    Nah - I wouldn't put it that way. It's no mistake or abuse. It's just
    one more example of a kernel making too few resources look sufficient
    by sharing, multiplexing and virtualizing them. That's what kernels do.

    I won't rest till it's the best ...
    Programmer, Linux Scalability
    Paul Jackson <> 1.925.600.0401
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      Last update: 2007-10-27 23:25    [W:0.021 / U:33.332 seconds]
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