Re: "VM watchdog"? [was Re: VM nuisance]

[David Ford <david@blue-labs.org>]

I think it is an excellent way to do it.  Nobody said you have to run 
the program and nobody forces you to use a particular program with a 
particular policy.  It puts the OOM policy in userland where -you- 
decide when and how things happen.

David

Jakob Østergaard wrote:

>>Maybe creating userland program that
>>*) allocates few megs
>>*) while 1 sleep 1m, gettimeofday. If more tha two minutes elapsed,
>>	tell OOM handler to kick in.
>>
>
>On my compute-server in the basement this is completely unacceptable because it
>*may* just be working hard on something big.  The excessive swapping may just
>be 10-30 minutes where some app is using way more memory than the box has RAM,
>in this case it's no problem at all, and all your suggestion would give me is
>randomly dying compute jobs.
>
>On my desktop this is unacceptable as well. You want the system to be frozen
>for more than two minutes before doing anything about it ?
>
>The problem with using such vague heuristics against fixed (arbitrary) limits
>is that the effect will almost always be completely unacceptable.  Either your
>arbitrary limit is way too high, or way too low.
>
>I can't tell you how to do it - but I think your suggestion is an excellent way
>to *not* do it     :)
>
>>Or maybe kernel could have some "VM watchdog", which would trigger OOM if
>>it is not polled once a minute...
>>
>
>Didn't everyone pretty much agree that if we could turn off overcommit
>completely and reliably, that would be the preferred solution ?   Simply sig11
>the app that's unlucky enough to want more memory than there's in the system
>(or, horror, have malloc() fail)
>
>Now, I don't remember the entire thread, but IIRC it was difficult to kill
>overcommit completely.
>

The kernel allocates memory within itself.  We will still reach OOM 
conditions.  It can't be avoided.

David