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

    > Den 13-Mar-00 14:14:19 skrev Khimenko Victor følgende om "Re: Overcomittable memory (Was: Linux 2.2.15pre12)":
    > > In <1404.107T1850T4774770rask@kampsax.k-net.dk> Rask Ingemann Lambertsen
    > > (rask@kampsax.k-net.dk) wrote:
    >
    > >> This doesn't mean that overcommit is a good idea. It just means that
    > >> fork()/exec() is not a good way of launching programs. Using overcommit to
    > >> cover up for fork()/exec() deficiencies is like redirecting compiler
    > >> warnings to /dev/null instead of fixing the code. The symptoms become less
    > >> visible but the problem remains. The problem could be solved by introducing
    > >> a new system call with the ability to start an external program as a new
    > >> process.
    >
    > > And then we should start playing stupid games with file descriptors. And
    > > then you can not spawn simple process to communicate with extenal program
    > > over net. And my 20 apache processes will require 800MiB of virtual memory
    > > instead of 60MiB they are using now.
    >
    > Where on Earth did you get those ideas from?

    Those 20 Apache processes each have 40Mb exclusively allocated to them.
    To honour that allocation without overcommit requires 20*40 = 800Mb of VM.

    > > Not every fork will end up with exec, you know.
    >
    > I don't think anybody said they do. I surely didn't.

    The problem is, that fork() allocates memory - the same amount as the
    parent process has allocated. If you want to honour this without
    overcommit, you must disable COW - otherwise you've overcommitted your
    memory.


    James.


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