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

From: Tejun Heo
Date: Thu Sep 24 2015 - 16:48:15 EST

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@xxxxxxxxxx>
> Reported-by: Artem Bityutskiy <dedekind1@xxxxxxxxx>
> Reported-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
> Link:
> Link:

Applying to cgroup/for-4.3-fixes.


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