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    SubjectRe: Overcommitable memory??
    On Sun, 19 Mar 2000, David Whysong wrote:
    >On Sun, 19 Mar 2000, Jesse Pollard wrote:
    >>On Sun, 19 Mar 2000, James Sutherland wrote:
    >>>On Sat, 18 Mar 2000 08:31:58 -0600, you wrote:
    >>>> Users (and processes) will get an Out-Of-Resource
    >>>> errors which the users can deal with.
    >>>In practice, they usually just die.
    >>The user still gets the choice.
    >No, this can't be allowed. What happens in the case of:
    > OOM -> signal processes Out of Resources
    > all processes decide to ignore the signal

    note: these are one specific user not the system - and what happens
    when they ignore the signal - they are aborted.

    >Once we are OOM, you can't give user-space any choices.

    YOU ARN'T OOM - a specific user is out of resources, not a catastrophic

    >Repeat after me:
    > You can not solve the OOM problem in user space.
    > You can not solve the OOM problem without killing processes.
    > Resource limits are not a good solution to the OOM problem.
    >I don't like resource limits. Using resource limits is similar to not
    >having memory overcommit -- you waste a lot of system resources "just in
    >case", the kernel needs to do a lot more accounting, and it's just
    >horribly inefficient.

    Resource limits CAN prevent the OOM condition if
    1. the sum of all concurrent users is <= total resources
    2. users are not allowed to exceed their quota

    >>>> If the proper resource allocation were given then usrs running wild
    >>>> memory allocators would not be able to crash the system by causing
    >>>> init to die.
    >>>They shouldn't be able to anyway - Rik's patch should ensure that init
    >>>will always survive, even if every other process on the box is hosed.
    >>>(Of course, if init was the malfunctioning process to begin with...)
    >If init malfunctions, you're hosed no matter what.

    It only aborts (normal situation) if the system is allowed to go OOM.

    >>>>All else is a matter of implementation.
    >>>The core problem remains. You, the user, have a finite amount of
    >>>memory available to you, however that limit is defined. Once you run
    >>>out, your processes will start dying.
    >But that's not the problem! That's the way things have to be. You can't
    >use more resources than there are available.

    No you can't - what you are doing is "giving" access to resources you
    don't have. When the resources are then accessed - you die; and the system
    with it.

    >>Yes - ME THE USER. I should not be able to cause the SYSTEM a problem.
    >>I should not be able to cause OTHER users a problem.
    >Ahh, no! You can only do this by setting up horribly restrictive quotas
    >and effectively removing overcommit, which is terribly wasteful!

    not horribly - It does appear that way when you have never been forced to
    live within a budget.

    >>>We need per-user resource limits, ideally - until then, everything is
    >>>done with process granularity instead. This is a shortcoming we all
    >>>know about already, but not one that is likely to be fixed any time
    >>That is possibly why the OOM complaints will not go away.
    >Well, my OOM complaints stem from the fact that right now OOM situations
    >are functionally equivalent to crashing the machine.

    Can't be helped much, as long as resource control is missing.
    Jesse I Pollard, II

    Any opinions expressed are solely my own.

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