Re: User space out of memory approach

[Bodo Eggert]

On Tue, 18 Jan 2005, Edjard Souza Mota wrote:

> > If my system needs the OOM killer, it's usurally unresponsive to most
> > userspace applications. A normal daemon would be swapped out before the
> > runaway dhcpd grows larger than the web cache. It would have to be a mlocked
> > RT task started from early userspace. It would be difficult to set up (unless
> > you upgrade your distro), and almost nobody will feel like tweaking it to
> > take the benefit (OOM == -ECANNOTHAPPEN).
> 
> Please correct me if I got it wrong: as deamon in this case is not a normal one,
> since it never gets rate for its own safety,

That's it's own task, it must make sure not to commit suicide. I forgot
about that.

> then it needs an RT lock whenever
> system boots.

It may not be blocked by a random RT task iff the RT task is supposed to
be OOM-killed. Therefore it *MUST* run at the highest priority and be
locked into the RAM.

It *SHOULD* be run at boot time, too, just in case it's needed early.

> > What about creating a linked list of (stackable) algorhithms which can be
> > extended by loading modules and resorted using {proc,sys}fs? It will avoid
> > the extra process, the extra CPU time (and task switches) to frequently
> > update the list and I think it will decrease the typical amount of used
> > memory, too.
> 
> Wouldn't this bring the (set of ) ranking algorithm(s) back to the kernel? This
> is exactly what we're trying to avoid.

You're trying to avoid it in order to let admins try other ranking
algorhithms (at least that's what I read). The module approach seems to be
flexible enough to do that, and it avoids the mentioned issues. If you
really want a userspace daemon, it can be controled by a module.-)

I 'm thinking of something like that:

[X] support stacking of OOM killer ranking algorhythms
[X] Task blessing OOM filter
[X] Userspace OOM ranking daemon
[X] Default OOM killer ranking

-vs-

[ ] support stacking of OOM killer ranking algorhythms
( ) Userspace OOM ranking daemon
(o) Default OOM killer ranking

-- 
Exceptions prove the rule, and destroy the battle plan. 
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