linux-kernel - Re: [Devel] [RFC PATCH 0/4] Container Freezer: Reuse Suspend Freezer

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Message-ID: <6599ad830804031649p6bbc60f3s59fb7c25a7260505@mail.gmail.com>
Date:	Thu, 3 Apr 2008 16:49:24 -0700
From:	"Paul Menage" <menage@...gle.com>
To:	matthltc@...ibm.com
Cc:	Linux-Kernel <linux-kernel@...r.kernel.org>,
	"Linux Containers" <containers@...ts.linux-foundation.org>
Subject: Re: [Devel] [RFC PATCH 0/4] Container Freezer: Reuse Suspend Freezer

On Thu, Apr 3, 2008 at 2:03 PM,  <matthltc@...ibm.com> wrote:
>
>    * "freezer.kill"
>
>      writing <n> will send signal number <n> to all tasks
>

My first thought (not having looked at the code yet) is that sending a
signal doesn't really have anything to do with freezing, so it
shouldn't be in the same subsystem. Maybe a separate subsystem called
"signal"?

And more than that, it's not something that requires any particular
per-process state, so there's no reason that the subsystem that
provides the "kill" functionality shouldn't be able to be mounted in
multiple hierarchies.

How about if I added support for stateless subsystems, that could
potentially be mounted in multiple hierarchies at once? They wouldn't
need an entry in the css set, since they have no state.

>  * Usage :
>
>    # mkdir /containers/freezer
>    # mount -t container -ofreezer freezer  /containers/freezer
>    # mkdir /containers/freezer/0
>    # echo $some_pid > /containers/freezer/0/tasks
>
>  to get status of the freezer subsystem :
>
>    # cat /containers/freezer/0/freezer.freeze
>    RUNNING
>
>  to freeze all tasks in the container :
>
>    # echo 1 > /containers/freezer/0/freezer.freeze
>    # cat /containers/freezer/0/freezer.freeze
>    FREEZING
>    # cat /containers/freezer/0/freezer.freeze
>    FROZEN

Could we separate this out into two files? One called "freeze" that's
a 0/1 for whether we're intending to freeze the subsystem, and one
called "frozen" that indicates whether it is frozen? And maybe a
"state" file to report the RUNNING/FREEZING/FROZEN distinction in a
human-readable way?

Paul
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