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SubjectRe: out_of_memory() heuristic broken for different mem configurations


On Tue, 6 Nov 2001, Stephan von Krawczynski wrote:

> On Tue, 6 Nov 2001 09:40:51 -0200 (BRST) Marcelo Tosatti
> <marcelo@conectiva.com.br> wrote:
>
> > Well, yes, its seems to be just a wrong magic number for this
> > setup/workload.
>
> Well, first time I read the code I thought that this will happen. Simply think
> of a _slow_ system with _lots_ of mem. Chances are high you cannot match the
> seconds-rule.
>
> > Linus, any suggestion to "fix" that ?
>
> How about this really stupid idea: oom means allocs fail, so why not simply
> count failed 0-order allocs, if one succeeds, reset counter. If a page is freed
> reset counter. If counter reaches <new magic number> then you're oom. No timing
> involved, which means you can have as much mem or as slow host as you like.

> It isn't even really interesting, if you have swap or not, because a
> failed 0-order alloc tells you whatever mem you have, there is surely
> not much left.

Wrong. If we have swap available, we are able to swapout anonymous data,
so we are _not_ OOM. This is an important point on this whole OOM killer
nightmare.

Keep in mind that we don't want to destroy anonymous data from userspace
(OOM kill).

> I'd try about 100 as magic number.

I think your suggestion will work well in practice (except that we have to
check the swap).

I'll try that later.

> > /proc tunable (eeek) ?
>
> NoNoNo, please don't do that!

Note that even if your suggestion works, we may want to make the magic
value /proc tunable.

The thing is that the point where tasks should be killed is also an admin
decision, not a complete kernel decision.

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