Re: [PATCH 4/4] Allow cgroup hierarchies to be created with no bound subsystems

[Li Zefan <lizf@cn.fujitsu.com>]

Paul Menage wrote:
> Allow cgroup hierarchies to be created with no bound subsystems
> 
> This patch removes the restriction that a cgroup hierarchy must have
> at least one bound subsystem.  The mount option "none" is treated as
> an explicit request for no bound subsystems.
> 
> A hierarchy with no subsystems can be useful for plain task tracking,
> and is also a step towards the support for multiply-bindable
> subsystems.
> 
> As part of this change, the hierarchy id is no longer calculated from
> the bitmask of subsystems in the hierarchy (since this is not
> guaranteed to be unique) but is allocated via an ida.  Reference
> counts on cgroups from css_set objects are now taken explicitly one
> per hierarchy, rather than one per subsystem.
> 
> Example usage:
> 
> mount -t cgroup -o none,name=foo cgroup /mnt/cgroup
> 
> Based on the "no-op"/"none" subsystem concept proposed by
> kamezawa.hiroyu@jp.fujitsu.com
> 
> Signed-off-by: Paul Menage <menage@google.com>
> 

Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>