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    Subjectkiobuf mapping with "mem=" boot option

    We have an application which uses a separate pool of
    memory not managed by linux (reserved using "mem="
    option at boot command line) and a memory manager
    which manages this pool of memory in user space. The
    algorithm works like this:

    a. use "mem=xM" option to boot command line
    b. mmap() the memory above "xM" till end of actual RAM
    in user space application.
    c. the mmaped region is managed by a user space memory

    This works fine for the application.

    1. Now we want to access a chunk of memory which we
    allocated using the user level memory manager in
    kernel space also. For this we tried kiobuf approach
    on the memory which was allocated in user space. But
    this approach doesn't seem to work on this mmaped
    memory (map_user_kiobuf() gives EFAULT: Bad Address).
    Is this valid behaviour?

    2. Also, will we be wrong in making the assumption
    that the pages for memory above x Megs will never be
    swapped out?

    If the answer to question 1 above is, that memory
    which is beyond x Megs (mem=xM) can not be used for
    kiobuf mapping, then is it ok if we directly access
    the user space address from kernel space (assuming the
    answer to question 2 is yes).

    Any information in this regard will be of great help.

    Thanks in advance.

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