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Date:	Thu, 24 Sep 2015 16:48:06 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Artem Bityutskiy <dedekind1@...il.com>
Cc:	Theodore Ts'o <tytso@....edu>, axboe@...nel.dk,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	lizefan@...wei.com, cgroups@...r.kernel.org, hannes@...xchg.org,
	kernel-team@...com, adilger.kernel@...ger.ca,
	linux-ext4@...r.kernel.org, Dexuan Cui <decui@...rosoft.com>
Subject: Re: [PATCH cgroup/for-4.3-fixes] cgroup, writeback: don't enable
 cgroup writeback on traditional hierarchies

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@...nel.org>
> Reported-by: Artem Bityutskiy <dedekind1@...il.com>
> Reported-by: Dexuan Cui <decui@...rosoft.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
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