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SubjectRe: Overcommitable memory??
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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
failure.

>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
>>>soon.
>>
>>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
Email: pollard@cats-chateau.net
Any opinions expressed are solely my own.

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