Re: [PATCH cgroup/for-4.3-fixes] cgroup, writeback: don't enable cgroup writeback on traditional hierarchies

[Tejun Heo <tj@kernel.org>]

On Wed, Sep 23, 2015 at 05:07:29PM -0400, Tejun Heo wrote:
> inode_cgwb_enabled() gates cgroup writeback support.  If it returns
> true, each inode is attached to the corresponding memory domain which
> gets mapped to io domain.  It currently only tests whether the
> filesystem and bdi support cgroup writeback; however, cgroup writeback
> support doesn't work on traditional hierarchies and thus it should
> also test whether memcg and iocg are on the default hierarchy.
> 
> This caused traditional hierarchy setups to hit the cgroup writeback
> path inadvertently and ended up creating separate writeback domains
> for each memcg and mapping them all to the root iocg uncovering a
> couple issues in the cgroup writeback path.
> 
> cgroup writeback was never meant to be enabled on traditional
> hierarchies.  Make inode_cgwb_enabled() test whether both memcg and
> iocg are on the default hierarchy.
> 
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Reported-by: Artem Bityutskiy <dedekind1@gmail.com>
> Reported-by: Dexuan Cui <decui@microsoft.com>
> Link: http://lkml.kernel.org/g/1443012552.19983.209.camel@gmail.com
> Link: http://lkml.kernel.org/g/f30d4a6aa8a546ff88f73021d026a453@SIXPR30MB031.064d.mgd.msft.net

Applying to cgroup/for-4.3-fixes.

Thanks.

-- 
tejun