linux-kernel - Re: [RFC][PATCH] NOOP cgroup subsystem

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Message-Id: <20090120120728.9be81131.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Tue, 20 Jan 2009 12:07:28 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Paul Menage <menage@...gle.com>
Cc:	matthltc@...ibm.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"lizf@...fujitsu.com" <lizf@...fujitsu.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	Containers <containers@...ts.linux-foundation.org>
Subject: Re: [RFC][PATCH] NOOP cgroup subsystem

On Mon, 19 Jan 2009 17:52:36 -0800
Paul Menage <menage@...gle.com> wrote:

> On Thu, Jan 15, 2009 at 6:20 PM, Matthew Helsley <matthltc@...ibm.com> wrote:
> >
> >        My feeling is this should be a signal subsystem rather than a NOOP
> > subsystem. Then, if users want the grouping for something besides
> > signaling, it doesn't matter if they don't issue any signals via the
> > signal.send file. Also, I think Paul's suggestion would be just as
> > useful for a signal subsystem.
> 
> The signal subsystem is similar to the "no-op" subsystem in that
> neither of them actually need any state - in principle, it could be
> useful to attach a signal subsys to multiple mounted hierarchies, to
> provide signal semantics for each of them.
> 
In my understanding, "sending signal" requires some protocol/order in userland.

Assume that users has to send signal in following order
  Application A -> Application B -> Application C.....
and may have problems sending signals in following order
  Application B -> Application A ->.....

So, signal and noop(just classify apps) is not equivalent in this semantics.

> Would it make sense to allow a class of subsystem that explicitly has
> no state (or at least, has no state that has a global meaning on the
> machine), so that it can be multiply-mounted?
> 
multilply-mounted means its own hierachy can be created per mount point ?
If so, signal subsystem can be used instead of noop.

Thanks,
-Kame

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