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    SubjectRe: clustering page-ins
    Chuck Lever wrote:
    > true. but i'm also worried about sharing the read-ahead information
    > amongst all mappers of a shared file. this case has come up in my
    > benchmarking (although i haven't tracked it down, it is occurring in some
    > basic commands that are run by the benchmark).

    Since each mapping has its own vm_area, I don't see the problem.
    Do you want different mappers to share read-ahead info?

    > so, i think the information needs to be in the file struct so that shared
    > maps don't continue to read ahead a file that is already in the page
    > cache.

    Sorry I don't quite understand what you want here. If you want to share
    read-ahead info between different mappers, struct file isn't going to do
    it -- each new open() creates a new struct file. If you don't, vm_area
    and struct file won't make much difference.

    It's only when you consider multiple mappings made from the same file
    descriptor (or passed through fork/exec) that there's a difference: then
    struct file leads to sharing while vm_area does not. There's also the
    matter of files mapped and read with read() (e.g. ELF executables).

    -- Jamie

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