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    SubjectRe: [PATCH 1/2] rcfs core patch
    Herbert wrote:
    > why is the filesystem approach so favored for this
    > kind of manipulations?

    I don't have any clear sense of whether the additional uses of file
    systems being considered here are a good idea or not, but the use of a
    file system for cpusets has turned out quite well, in my (vain and
    biased ;) view.

    Cpusets are subsets of the CPUs and memory nodes on a system.

    These subsets naturally form a partial ordering, where one cpuset is
    below another if its CPUs and nodes are a subset of the other ones.

    This forms a natural hierarchical space. It is quite convenient to be
    able to add names and file system like attributes, so that one can do
    things like -name- the set of CPUs to which you are attaching a job, as
    in "this job is to run on the CPUs in cpuset /foo/bar", and to further
    have file system like permissions on these subsets, to control who can
    access or modify them.

    For such hierarchical data structures, especially ones where names and
    permissions are useful, file systems are a more natural interface than
    traditional system call usage patterns.

    The key, in my view, is the 'shape' of the data. If the data schema is
    basically a single table, with uniform rows having a few fields each,
    where each field is a simple integer or string (not a fancy formatted
    string encoding some more elaborate shape) then classic system call
    patterns work well. If the schema is tree shaped, and especially if
    the usual file system attributes such as a hierarchical name space and
    permissions are useful, then a file system based API is probably best.

    --
    I won't rest till it's the best ...
    Programmer, Linux Scalability
    Paul Jackson <pj@sgi.com> 1.925.600.0401
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