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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