Re: Andrea VM changes

[Andrea Arcangeli]

On Sun, Aug 31, 2003 at 03:10:04PM +0100, Alan Cox wrote:
> On Sul, 2003-08-31 at 00:19, Andrea Arcangeli wrote:
> > I've an algorithm that will work, and that will provide very good
> > guarantees to kill the "best" task to make the machine usable again,
> > with the needed protection against the security DoSes, but it's in
> > no-way similar to the current oom killer.
> 
> And -ac has trivial code so you can avoid OOM killing every happening,
> which is pretty much essential for big servers. Perhaps merging that
> as well would be a good idea.

the reservation that you've to do can generate a less optimal
utilization of ram (some buggy app can also fail with it), but I agree
it's a nice feature to be able to return -ENOMEM out of malloc (for
desktops too), instead of killing the task.

However you have the exact same oom deadlocks problem with all non
userspace allocations, like a select, select will deadlock the box in
-ac if you're out of lowmemory, no matter of the non-overcommit
behaviour, same goes for mlock.

And I don't see how you can avoid oom killing to ever happen if the apps
recurse on the stack and growsdown some hundred megs. In such case
you've to oom kill, since there's no synchronous failure path during the
stack growsdown walk.

this of course doesn't change the fact that providing the non overcommit
behaviour (optional), sounds a very good idea, I'm all for it.

I just don't think it solves or hides the other issues, it seems
completely orthogonal to me, because you can still run oom during stack
growsdown.

Andrea
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