• Tejun Heo's avatar
    cgroup: mark subsystems with broken hierarchy support and whine if cgroups are nested for them · 8c7f6edb
    Tejun Heo authored
    
    
    Currently, cgroup hierarchy support is a mess.  cpu related subsystems
    behave correctly - configuration, accounting and control on a parent
    properly cover its children.  blkio and freezer completely ignore
    hierarchy and treat all cgroups as if they're directly under the root
    cgroup.  Others show yet different behaviors.
    
    These differing interpretations of cgroup hierarchy make using cgroup
    confusing and it impossible to co-mount controllers into the same
    hierarchy and obtain sane behavior.
    
    Eventually, we want full hierarchy support from all subsystems and
    probably a unified hierarchy.  Users using separate hierarchies
    expecting completely different behaviors depending on the mounted
    subsystem is deterimental to making any progress on this front.
    
    This patch adds cgroup_subsys.broken_hierarchy and sets it to %true
    for controllers which are lacking in hierarchy support.  The goal of
    this patch is two-fold.
    
    * Move users away from using hierarchy on currently non-hierarchical
      subsystems, so that implementing proper hierarchy support on those
      doesn't surprise them.
    
    * Keep track of which controllers are broken how and nudge the
      subsystems to implement proper hierarchy support.
    
    For now, start with a single warning message.  We can whine louder
    later on.
    
    v2: Fixed a typo spotted by Michal. Warning message updated.
    
    v3: Updated memcg part so that it doesn't generate warning in the
        cases where .use_hierarchy=false doesn't make the behavior
        different from root.use_hierarchy=true.  Fixed a typo spotted by
        Glauber.
    
    v4: Check ->broken_hierarchy after cgroup creation is complete so that
        ->create() can affect the result per Michal.  Dropped unnecessary
        memcg root handling per Michal.
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Acked-by: default avatarMichal Hocko <mhocko@suse.cz>
    Acked-by: default avatarLi Zefan <lizefan@huawei.com>
    Acked-by: default avatarSerge E. Hallyn <serue@us.ibm.com>
    Cc: Glauber Costa <glommer@parallels.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Paul Turner <pjt@google.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Thomas Graf <tgraf@suug.ch>
    Cc: Vivek Goyal <vgoyal@redhat.com>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
    Cc: Neil Horman <nhorman@tuxdriver.com>
    Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    8c7f6edb