On Friday, 1 of August 2008, Matt Helsley wrote:
> This patch implements a new freezer subsystem in the control groups framework.
> It provides a way to stop and resume execution of all tasks in a cgroup by
> writing in the cgroup filesystem.
>
> The freezer subsystem in the container filesystem defines a file named
> freezer.state. Writing "FROZEN" to the state file will freeze all tasks in the
> cgroup. Subsequently writing "RUNNING" will unfreeze the tasks in the cgroup.
> Reading will return the current state.
>
> * Examples of usage :
>
> # mkdir /containers/freezer
> # mount -t cgroup -ofreezer freezer /containers
> # mkdir /containers/0
> # echo $some_pid > /containers/0/tasks
>
> to get status of the freezer subsystem :
>
> # cat /containers/0/freezer.state
> RUNNING
>
> to freeze all tasks in the container :
>
> # echo FROZEN > /containers/0/freezer.state
> # cat /containers/0/freezer.state
> FREEZING
> # cat /containers/0/freezer.state
> FROZEN
>
> to unfreeze all tasks in the container :
>
> # echo RUNNING > /containers/0/freezer.state
> # cat /containers/0/freezer.state
> RUNNING
>
> This is the basic mechanism which should do the right thing for user space task
> in a simple scenario.
>
> It's important to note that freezing can be incomplete. In that case we return
> EBUSY. This means that some tasks in the cgroup are busy doing something that
> prevents us from completely freezing the cgroup at this time. After EBUSY,
> the cgroup will remain partially frozen -- reflected by freezer.state reporting
> "FREEZING" when read. The state will remain "FREEZING" until one of these
> things happens:
>
> 1) Userspace cancels the freezing operation by writing "RUNNING" to
> the freezer.state file
> 2) Userspace retries the freezing operation by writing "FROZEN" to
> the freezer.state file (writing "FREEZING" is not legal
> and returns EIO)
> 3) The tasks that blocked the cgroup from entering the "FROZEN"
> state disappear from the cgroup's set of tasks.
>
> Signed-off-by: Cedric Le Goater <clg@xxxxxxxxxx>
> Signed-off-by: Matt Helsley <matthltc@xxxxxxxxxx>
> Acked-by: Serge E. Hallyn <serue@xxxxxxxxxx>
> Tested-by: Matt Helsley <matthltc@xxxxxxxxxx>
> ---
> include/linux/cgroup_freezer.h | 71 ++++++++
> include/linux/cgroup_subsys.h | 6
> include/linux/freezer.h | 16 +-
> init/Kconfig | 7
> kernel/Makefile | 1
> kernel/cgroup_freezer.c | 328 +++++++++++++++++++++++++++++++++++++++++
> 6 files changed, 425 insertions(+), 4 deletions(-)
> create mode 100644 include/linux/cgroup_freezer.h
> create mode 100644 kernel/cgroup_freezer.c
>
> Index: linux-2.6.27-rc1-mm1/include/linux/cgroup_freezer.h
> ===================================================================
> --- /dev/null
> +++ linux-2.6.27-rc1-mm1/include/linux/cgroup_freezer.h
> @@ -0,0 +1,71 @@
> +#ifndef _LINUX_CGROUP_FREEZER_H
> +#define _LINUX_CGROUP_FREEZER_H
> +/*
> + * cgroup_freezer.h - control group freezer subsystem interface
> + *
> + * Copyright IBM Corporation, 2007
> + *
> + * Author : Cedric Le Goater <clg@xxxxxxxxxx>
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of version 2.1 of the GNU Lesser General Public License
> + * as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it would be useful, but
> + * WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
> + */
> +
> +#include <linux/cgroup.h>
> +
> +#ifdef CONFIG_CGROUP_FREEZER
> +
> +enum freezer_state {
> + STATE_RUNNING = 0,
> + STATE_FREEZING,
> + STATE_FROZEN,
> +};
> +
> +struct freezer {
> + struct cgroup_subsys_state css;
> + enum freezer_state state;
> + spinlock_t lock; /* protects _writes_ to state */
> +};
> +
> +static inline struct freezer *cgroup_freezer(
> + struct cgroup *cgroup)
> +{
> + return container_of(
> + cgroup_subsys_state(cgroup, freezer_subsys_id),
> + struct freezer, css);
> +}
> +
> +static inline struct freezer *task_freezer(struct task_struct *task)
> +{
> + return container_of(task_subsys_state(task, freezer_subsys_id),
> + struct freezer, css);
> +}
> +
> +static inline int cgroup_frozen(struct task_struct *task)
> +{
> + struct freezer *freezer;
> + enum freezer_state state;
> +
> + task_lock(task);
> + freezer = task_freezer(task);
> + state = freezer->state;
> + task_unlock(task);
> +
> + return state == STATE_FROZEN;
> +}
> +
> +#else /* !CONFIG_CGROUP_FREEZER */
> +
> +static inline int cgroup_frozen(struct task_struct *task)
> +{
> + return 0;
> +}
> +
> +#endif /* !CONFIG_CGROUP_FREEZER */
> +
> +#endif /* _LINUX_CGROUP_FREEZER_H */
Hmm. I wonder if we really need a separate file for this. I'd prefer it to be
in freezer.h, unless there's a good reason not to place it in there.
Thanks,
Rafael
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