Re: clarification about misc controller and capacity vs. max

["Accardi, Kristen C" <kristen.c.accardi-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>]

On Tue, 2022-11-01 at 06:54 -1000, tj@kernel.org wrote:
> Hello,
> 
> On Tue, Nov 01, 2022 at 04:40:22PM +0000, Accardi, Kristen C wrote:
> > I notice in the comments for the misc controller it is stated that
> > the
> > max limit can be more than actual total capacity, meaning that we
> > can
> > overcommit with the resource controlled by the misc controller.
> > However, in the misc_cg_try_charge() code, the function will return
> > -
> > EBUSY if max limit will be crossed or total usage will be more than
> > the
> > capacity, which would seem to enforce total capacity as an upper
> > limit
> > in addition to max and not allow for overcommit. Can you provide
> > some
> > clarity on whether the resource consumption model for the misc
> > controller should allow for overcommit?
> 
> I think what it's trying to say is that the sum of first level .max's
> can be
> higher than the total capacity. e.g. Let's say you have 5 of this
> resource
> and a hierarchy like the following.
> 
>         R - A - A'
>           + B - B'
>           \ C
> 
> It's valid to have A, B, C's max set to 4, 3, 2 respectively even if
> they
> sum up to 9 which is larger than what's available in the system, 5 -
> ie. the
> max limits are overcommitted for the resource.
> 
> Thanks.
> 

So to be clear, if I have this:

/sys/fs/cgroup/misc.capacity
some_res 10

and this:
/sys/fs/cgroup/test

test.current will never be allowed to exceed 10.