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SubjectRe: user defined OOM policies
On Mon 25-11-13 17:29:20, David Rientjes wrote:
> On Wed, 20 Nov 2013, Luigi Semenzato wrote:
> > Yes, I agree that we can't always prevent OOM situations, and in fact
> > we tolerate OOM kills, although they have a worse impact on the users
> > than controlled freeing does.
> >
> If the controlled freeing is able to actually free memory in time before
> hitting an oom condition, it should work pretty well. That ability is
> seems to be highly dependent on sane thresholds for indvidual applications
> and I'm afraid we can never positively ensure that we wakeup and are able
> to free memory in time to avoid the oom condition.
> > Well OK here it goes. I hate to be a party-pooper, but the notion of
> > a user-level OOM-handler scares me a bit for various reasons.
> >
> > 1. Our custom notifier sends low-memory warnings well ahead of memory
> > depletion. If we don't have enough time to free memory then, what can
> > the last-minute OOM handler do?
> >
> The userspace oom handler doesn't necessarily guarantee that you can do
> memory freeing, our usecase wants to do a priority-based oom killing that
> is different from the kernel oom killer based on rss. To do that, you
> only really need to read certain proc files and you can do killing based
> on uptime, for example. You can also do a hierarchical traversal of
> memcgs based on a priority.
> We already have hooks in the kernel oom killer, things like
> /proc/sys/vm/oom_kill_allocating_task

How would you implement oom_kill_allocating_task in userspace? You do
not have any context on who is currently allocating or would you rely on
reading /proc/*/stack to grep for allocation functions?

> and /proc/sys/vm/panic_on_oom that
Michal Hocko

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