linux-kernel - Re: [PATCH 2/2] ext4: implement cgroup writeback support

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Message-ID: <20150923170238.GG3318@thunk.org>
Date:	Wed, 23 Sep 2015 13:02:38 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Artem Bityutskiy <dedekind1@...il.com>
Cc:	Tejun Heo <tj@...nel.org>, 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
Subject: Re: [PATCH 2/2] ext4: implement cgroup writeback support

On Wed, Sep 23, 2015 at 04:50:53PM +0300, Artem Bityutskiy wrote:
> On Wed, 2015-09-23 at 15:49 +0300, Artem Bityutskiy wrote:
> > On Tue, 2015-07-21 at 23:56 -0400, Theodore Ts'o wrote:
> > > > v2: Updated for MS_CGROUPWB -> SB_I_CGROUPWB.
> > > > 
> > > > Signed-off-by: Tejun Heo <tj@...nel.org>
> > > > Cc: "Theodore Ts'o" <tytso@....edu>
> > > > Cc: Andreas Dilger <adilger.kernel@...ger.ca>
> > > > Cc: linux-ext4@...r.kernel.org
> > > 
> > > Thanks, applied.
> > 
> > Hi, this patch introduces a regression - a major one, I'd say.
> > 
> > Symptoms: copy a bunch of file, run sync, then run 'reboot', and
> > after
> > you boot up the copied files are corrupted. So basically the user
> > -visible symptom is that 'sync' does not work.
> 
> Just FYI, this is the issue I briefly reported last Fri:
> 
> https://lkml.org/lkml/2015/9/18/640

Also note this performance regression reported by Dexuan Cui

	https://lkml.org/lkml/2015/9/23/333

I didn't notice these problems since I my userspace doesn't enable the
writeback cgroup.  (In fact I don't know how to do it using Debian
Jessie.)

Tejun, can you please take a look at this and give me a
recommendation?  I'm willing to wait a day or two while we try to fix
the problem, but past that point I'd like to have a fix or revert this
commit before Linus releases the next -rc release.

						- Ted
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