Re: Overcommitable memory??

From: David Whysong (
Date: Sun Mar 19 2000 - 22:59:33 EST

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.


David Whysong
Astrophysics graduate student University of California, Santa Barbara
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