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SubjectRe: [PATCH 3/6] Container Freezer: Implement freezer cgroup subsystem
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On Saturday, 2 of August 2008, Cedric Le Goater wrote:
> Matt Helsley wrote:
> > On Sat, 2008-08-02 at 00:58 +0200, Rafael J. Wysocki wrote:
> >> 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@fr.ibm.com>
> >>> Signed-off-by: Matt Helsley <matthltc@us.ibm.com>
> >>> Acked-by: Serge E. Hallyn <serue@us.ibm.com>
> >>> Tested-by: Matt Helsley <matthltc@us.ibm.com>
> >>> ---
> >>> 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@fr.ibm.com>
> >>> + *
> >>> + * 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.
> >
> > Yeah, it's a pretty small header so combining it with another header
> > would be nice. However if we combine it with freezer.h we'd be including
> > cgroup.h in unrelated filesystem code. An alternative might be to put it
> > into a cgroup header for "small" subsystems (which might just be
> > cgroup.h for now..).
> >
> > Thanks for the review!
>
> I'm not sure the inline is really useful. In that case, we could probably do
> something like the following :
>
> include/linux/freezer.h :
>
> #ifdef CONFIG_CGROUP_FREEZER
>
> extern int cgroup_frozen(struct task_struct *task);
>
> #else /* !CONFIG_CGROUP_FREEZER */
>
> static inline int cgroup_frozen(struct task_struct *task)
> {
> return 0;
> }
>
> #endif /* !CONFIG_CGROUP_FREEZER */
>
> and in kernel/cgroup_freezer.c:
>
> 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;
> }
>
> and kill include/linux/cgroup_freezer.h ?

I'd prefer this.

Thanks,
Rafael


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