linux-kernel - Re: [RFC PATCH 4/4] cgroups: Add an rlimit subsystem

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Message-ID: <20110623134759.GC8058@somewhere.redhat.com>
Date:	Thu, 23 Jun 2011 15:48:04 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Paul Menage <menage@...gle.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Li Zefan <lizf@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 4/4] cgroups: Add an rlimit subsystem

On Tue, Jun 21, 2011 at 10:37:03AM -0700, Paul Menage wrote:
> On Sun, Jun 19, 2011 at 4:51 PM, Frederic Weisbecker <fweisbec@...il.com> wrote:
> > +static void rlim_cgroup_exit(struct cgroup_subsys *ss, struct cgroup *cgrp,
> > +                     struct cgroup *old_cgrp, struct task_struct *task)
> > +{
> > +       rlim_remove_proc(old_cgrp);
> > +}
> 
> Since this is used for both the exit callback and the attach callback,
> it should have a more generic name.

Right.
 
> > +static int rlim_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
> > +{
> > +       struct rlim *rlim = cgroup_rlim(cgrp);
> > +       struct res_counter *limit_fail_at;
> > +
> > +       return res_counter_charge(&rlim->proc_counter, 1, &limit_fail_at);
> > +}
> 
> Can't this fail spuriously in the presence of hierarchies?
> 
> E.g. if cgroup A has children, and A is at its limit, then moving
> tasks around between A and its children, or between different children
> of A, seems like it would fail due to the temporary double counting.

Good point. Probably I should first uncharge the old cgroup and its parents.
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