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    SubjectRe: Overcommitable memory??
    On 15 Mar 2000, Rask Ingemann Lambertsen wrote:

    > Den 14-Mar-00 18:32:49 skrev Rik van Riel følgende om "Re: Overcommitable memory??":
    > > On 13 Mar 2000, Rask Ingemann Lambertsen wrote:
    > [program crash because demand loading fails due to no memory]
    > >> Without overcommit that just can not happen. There will be
    > >> either a free page of memory or a free page of swap into which
    > >> you can swap something else out.
    > > Without overcommit it can still happen, unless you reserve one
    > > page of swap space for every page of data that gets mmap()ed...
    > Not having swap or RAM for every page of mmap()ed data means that you
    > are overcommitting memory. If you're mmap()ing a file, then that file can
    > count as swap too. Files with "holes" in them may be a problem.

    Overcommitting memory is not the problem I have in mind here.

    > >> Please realize that the only gain from overcomitting memory
    > >> is that yoy may get away with having less swap space. The
    > >> downside you get is random program crashes, lost work, etc.
    > > 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. Lost work will only happen due to user
    > errors, software bugs or hardware problems. If you overcommit memory, you
    > can lose the file you were editing in emacs simply because someone sent you
    > an email and the MTA needed a bit of memory to deliver it to you. Some
    > people, myself included, just don't find that acceptable at all.

    You can still run out of memory, with or without COW, overcommit etc. I
    think we are talking at cross purposes here: By running out of memory, I
    mean there isn't any free memory to give to apps requesting it (via
    malloc() etc.)

    If Netscape blows up and grabs all my memory, other applications can't get
    any - so I have problems. I need Netscape to be killed to fix the problem
    - and I can't log in to do it manually. THIS is the OOM situation I am
    thinking of, not a kernel-level problem of being unable to handle a page


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