Re: [PATCH 2/3] memcg: Limit the number of events registered onoom_control

From: Michal Hocko
Date: Wed Aug 07 2013 - 09:57:42 EST

On Wed 07-08-13 09:47:41, Tejun Heo wrote:
> Hello,
> On Wed, Aug 07, 2013 at 03:37:46PM +0200, Michal Hocko wrote:
> > > It isn't different from listening from epoll, for example.
> >
> > epoll limits the number of watchers, no?
> Not that I know of. It'll be limited by max open fds but I don't
> think there are other limits.

max_user_watches seems to be a limit (4% of lowmem in maximum).

> Why would there be?

Because userspace should hog kernel resources without any limit.

> > > If there needs to be kernel memory limit, shouldn't that be handled by
> > > kmemcg?
> >
> > kmemcg would surely help but turning it on just because of potential
> > abuse of the event registration API sounds like an overkill.
> >
> > I think having a cap for user trigable kernel resources is a good thing
> > in general.
> I don't know. It's just very arbitrary because listening to events
> itself isn't (and shouldn't) be something which consumes resource
> which isn't attributed to the listener and this artificially creates a
> global resource. The problem with memory usage event is breaching
> that rule with shared kmalloc() so putting well-defined limit on it is
> fine but the latter two create additional artificial restrictions
> which are both unnecessary and unconventional. No?

Hmm, OK so you think that the fd limit is sufficient already?
Michal Hocko
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