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    SubjectRe: [PATCH 5/7] cgroups: Make freezer subsystem bindable
    Matt Helsley wrote:
    > On Fri, Oct 22, 2010 at 04:11:41PM +0800, Li Zefan wrote:
    >> To make it bindable, we need to thaw all processes when unbinding
    >> the freezer subsystem from a cgroup hierarchy.
    >>
    >> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
    >
    > Based on experience using cgroups and questions we've fielded in the
    > past on IRC I'd say users will really appreciate this.
    >
    > We're planning to use the freezer in checkpoint/restart. Since
    > checkpoint requires the tasks to remain frozen for the duration of
    > the syscall we add a kernel-internal freezer subsystem interface
    > which prevents the cgroup from thawing. So we'll need some way to
    > "block" unbinding for that as well.
    >

    How about, we allow unbinding only when all the cgroups' state is
    THAWED ?

    > Perhaps the bind op should be able to return an error when
    > unbind == true? Although that raises the question of what to do if
    > only one of multiple unbinds fails..
    >
    > Alternately you could split the bind/unbind op function pointers
    > and get rid of the boolean argument. Then just don't fill in the
    > freezer's unbind op and refuse to unbind subsystems that lack
    > the unbind op. That seems a bit cleaner for now at least.
    >

    We can use bindable:1 along with a callback can_bind().

    For some subsystems, we just set bindable to true. For freezer subsystem,
    we set it to true and provide freezer_can_bind(), and return true only
    if no cgroup's state is FROZEN.


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