lkml.org 
[lkml]   [1999]   [Jan]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: Linux and physical memory
    On Sun, 17 Jan 1999, Kurt Garloff wrote:

    >On Sun, Jan 17, 1999 at 02:44:37PM +0100, Max wrote:
    >>
    >> Maybe I am stupid, but while I understand this is correct (i.e. reserve a part
    >> of processes address space to point to kernel code/data), I don't
    >> understand why the kernel needs to always have all physical memory mapped
    >> in its address space.
    >
    >Because you perform a syscall, say for I/O, and tell the kernel: Hey, put
    >this into this buffer. Now, what woul the kernel do, if the memory is not
    >mapped? How should the kernel start a binary, if it can not access the
    >memory, where it's started.
    >If the kernel does not map the memory, it cannot control it.
    >The only way out is to use other selectors and to have context switches,
    >which would hurt performance, as said before.
    >I don't think, that's what we want.

    Even if english is not my native language, I thought my question was clear:

    >> I don't understand why the kernel needs to always have all physical memory
    >> mapped in its address space.

    I said "ALWAYS have mapped ALL physical memory" etc.

    So I obviously mean (well, lokkgin to your answer maybe it was not so obvious):

    Why can't the kernel just map in its address space the pieces of RAM it needs
    for kernel code/data, and unmap them when done with them?
    User code/data would always be accessible (I am not suggesting to touch user
    processes address space) so I thought that could work and remove the 960MB
    problem.

    Maybe that mapping/unmapping of memory in kernel address space is expensive,
    but I don't know. So I posted the question.

    Massimiliano Ghilardi




    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.rutgers.edu
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2005-03-22 13:49    [W:0.020 / U:0.312 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site