Re: [RFC] How to handle the rules engine for cgroups

From: "Paul Menage" <menage@google.com>
To: "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@jp.fujitsu.com>
Cc: "Vivek Goyal" <vgoyal@redhat.com>,
	"linux kernel mailing list" <linux-kernel@vger.kernel.org>,
	"Libcg Devel Mailing List" <libcg-devel@lists.sourceforge.net>,
	"Balbir Singh" <balbir@linux.vnet.ibm.com>,
	"Dhaval Giani" <dhaval@linux.vnet.ibm.com>,
	"Peter Zijlstra" <pzijlstr@redhat.com>,
	"Kazunaga Ikeno" <k-ikeno@ak.jp.nec.com>,
	"Morton Andrew Morton" <akpm@linux-foundation.org>
Subject: Re: [RFC] How to handle the rules engine for cgroups
Date: Fri, 18 Jul 2008 08:46:55 -0700	[thread overview]
Message-ID: <6599ad830807180846n11260adft168bddf7c203469c@mail.gmail.com> (raw)
In-Reply-To: <20080718185226.f809281d.kamezawa.hiroyu@jp.fujitsu.com>

On Fri, Jul 18, 2008 at 2:52 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
>
> For example, create a new file under memory cgroup
> ==
>  /opt/memory_cgroup/group_A/notify_at_memory_reach_limit
> ==
> And a user watches the file by inotify.
> The kernel modify modified-time of notify_at_memory_reach_limit file and call
> fs/notify_user.c::notify_change() against this inode. He can catchthe event
> by inotify.
> (I think he can also catch removal of this file, etc...)
>

We've been doing something like this to handle OOMs in userspace, with
pretty good success. The approach that we used so far was a custom
control file tied to a wait queue, that gets woken when a cgroup
triggers OOM, but it's a bit hacky. I've been considering some kind of
more generic approach that could be reused by different subsystems for
other notifications, maybe using eventfd or maybe netlink.

inotify would be an option too, but that seems like it might be
forcing ourselves into filesystem semantics too much.

Paul