Re: Overcommitable memory??

From: David Whysong (dwhysong@physics.ucsb.edu)
Date: Sun Mar 19 2000 - 22:59:33 EST

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    On 19 Mar 2000, Rask Ingemann Lambertsen wrote:
    >Den 16-Mar-00 20:18:09 David Whysong wrote:
    >> On 15 Mar 2000, Rask Ingemann Lambertsen wrote:
    >>>Den 14-Mar-00 18:32:49 Rik van Riel wrote:

    >>>> Not really. Without overcommit you may still have random program
    >>>> crashes and lost work...
    >>>
    >>> Yes, really. Maybe I should have said "additional lost work" instead
    >>>of just "lost work". Without overcommit, program crashes will only
    >>>happen due software bugs or hardware problems.
    > ^^^^^^^^^^^^^^^^^
    >
    >> Not true. With no overcommit, you can still crash programs due to OOM
    >> situations.
    >
    > Sure, not all programs are bug free. But that's a whole lot different
    >from having the kernel kill processes just because the kernel fails to
    >perform basic bookkeeping.

    I said crash due to OOM, not due to bugs. I never said anything about bugs.

    You can't avoid memory overcommit without dealing with:
            1. mmap()'ed data
            2. stack growth
            3. kernel dynamic memory allocation

    ...and probably a host of other things I know nothing about. You're
    talking about adding a tremendous amount of overhead and complexity for no
    real benefit.

    >> Memory overcommit is here to stay. As I recall, Linux already used
    >> overcommit and COW when I started using it at version 0.99pl13.
    >
    > So what is /proc/sys/vm/overcommit_memory for, if not to make
    >overcommitment of memory an _option_?

    It has already been shown on this list that

    # echo 0 > /proc/sys/vm/overcommit_memory

    does not, in fact, disable memory overcommit.

    >> Get used to it, or find another OS...
    >
    > You're such a good Linux advocate...

    Hey, this is core stuff that has been in the kernel for a very long time.
    It's not going to change, and it shouldn't be changed.

    Dave

    David Whysong dwhysong@physics.ucsb.edu
    Astrophysics graduate student University of California, Santa Barbara
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