linux-kernel - Re: [PATCH RFC 0/2] add nproc cgroup subsystem

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Message-ID: <CAAAKZws=k20ibx-EHumTyRwJ3TbpzeKwUNqWTAP5d+W1-mx-kw@mail.gmail.com>
Date:	Sat, 28 Feb 2015 20:46:13 -0800
From:	Tim Hockin <thockin@...kin.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Austin S Hemmelgarn <ahferroin7@...il.com>,
	Li Zefan <lizefan@...wei.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Aleksa Sarai <cyphar@...har.com>,
	Cgroups <cgroups@...r.kernel.org>, mingo <mingo@...hat.com>,
	richard <richard@....at>
Subject: Re: [PATCH RFC 0/2] add nproc cgroup subsystem

On Feb 28, 2015 2:50 PM, "Tejun Heo" <tj@...nel.org> wrote:
>
> On Sat, Feb 28, 2015 at 02:26:58PM -0800, Tim Hockin wrote:
> > Wow, so much anger.  I'm not even sure how to respond, so I'll just
> > say this and sign off.  All I want is a better, friendlier, more
> > useful system overall.  We clearly have different ways of looking at
> > the problem.
>
> Can you communicate anything w/o passive aggression?  If you have a
> technical point, just state that.  Can you at least agree that we
> shouldn't be making design decisions based on 16bit pid_t?

Hmm, I have screwed this thread up, I think.  I've made some remarks
that did not come through with the proper tongue-in-cheek slant.  I'm
not being passive aggressive - we DO look at this problem differently.
OF COURSE we should not make decisions based on ancient artifacts of
history.  My point was that there are secondary considerations here -
PIDs are more than just the memory that backs them.  They _ARE_ a
constrained resource, and you shouldn't assume the constraint is just
physical memory.  It is a piece of policy that is outside the control
of the kernel proper - we handed those keys to userspace along time
ago.

Given that, I believe and have believed that the solution should model
the problem as the user perceives it - limiting PIDs - rather than
attaching to a solution-by-proxy.

Yes a solution here partially overlaps with kmemcg, but I don't think
that is a significant problem.  They are different policies governing
behavior that may result in the same condition, but for very different
reasons.  I do not think that is particularly bad for overall
comprehension, and I think the fact that this popped up yet again
indicates the existence of some nugget of user experience that is
worth paying consideration to.

I appreciate your promised consideration through a slightly refocused
lens.  I will go back to my cave and do something I hope is more
productive and less antagonistic.  I did not mean to bring out so much
vitriol.

Tim
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