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    SubjectRe: Linux 2.2.15pre12

    Very correct. Sorry. :)

    On Mon, 6 Mar 2000, Paul Jakma wrote:

    > On Mon, 6 Mar 2000, Gregory Maxwell wrote:
    >
    > Yes, you can currently do this. Turning off overcommit doesn't stop COW,
    > but it takes away it's memory/swap advantage.
    >
    > [snip]
    > > as i understand you can't turn off overcommit in linux at the
    > > moment. Yet it would be a useful option to have. I can easily imagine
    > > certain situations where i would choose to turn off overcommit at the
    > > expense of more swap if it would guarantee that OOM would never
    > > happen. (hard disk space is cheap compared to downtime)
    > [snip]
    >
    > /proc/sys/vm/overcommit_memory
    > overcommit_memory:
    >
    > This value contains a flag that enables memory overcommitment.
    > When this flag is 0, the kernel checks before each malloc()
    > to see if there's enough memory left. If the flag is nonzero,
    > the system pretends there's always enough memory.
    >
    > This feature can be very useful because there are a lot of
    > programs that malloc() huge amounts of memory "just-in-case"
    > and don't much of it.
    >
    > i think you're misunderstanding the overcommit_memory sysctl. From
    > the wording above, the default of 0 gives us the normal (relaxed)
    > linux VM allocation policy. Setting it to > 0 *turns off* this
    > checking even altogether!!!
    >
    > Look at: mm/mmap.c::vm_enough_memory() for more information.
    >
    >
    > =>
    >
    > /* Sometimes we want to use more memory than we have. */
    > if (sysctl_overcommit_memory)
    > return 1;
    >
    > ie if overcommit_memory != 0 then we throw the already sparse
    > accounting checks out of the window. It does not turn off
    > overcommit!! It makes linux VM even more relaxed!!!
    >
    > regards,
    > --
    > Paul Jakma paul@clubi.ie
    > PGP5 key: http://www.clubi.ie/jakma/publickey.txt
    > -------------------------------------------
    > Fortune:
    > I am a friend of the working man, and I would rather be his friend
    > than be one.
    > -- Clarence Darrow
    >
    >


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