From: Dexuan Cui <decui@microsoft.com>
Subject: RE: ext4: performance regression introduced by the cgroup writeback
 support
Date: Thu, 24 Sep 2015 07:26:20 +0000
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To: Tejun Heo <tj@kernel.org>, Chris Mason <clm@fb.com>,
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> From: Dexuan Cui
> Sent: Thursday, September 24, 2015 8:16
> To: 'Tejun Heo' <tj@kernel.org>; Chris Mason <clm@fb.com>; Theodore Ts'o
> <tytso@mit.edu>; Andreas Dilger <adilger.kernel@dilger.ca>; linux-
> ext4@vger.kernel.org; linux-fsdevel@vger.kernel.org; linux-
> kernel@vger.kernel.org
> Subject: RE: ext4: performance regression introduced by the cgroup writeback
> support
> 
> > -----Original Message-----
> > From: Tejun Heo [mailto:htejun@gmail.com] On Behalf Of Tejun Heo
> > Sent: Thursday, September 24, 2015 2:54
> > To: Chris Mason <clm@fb.com>; Dexuan Cui <decui@microsoft.com>;
> > Theodore Ts'o <tytso@mit.edu>; Andreas Dilger <adilger.kernel@dilger.ca>;
> > linux-ext4@vger.kernel.org; linux-fsdevel@vger.kernel.org; linux-
> > kernel@vger.kernel.org
> > Subject: Re: ext4: performance regression introduced by the cgroup writeback
> > support
> >
> > On Wed, Sep 23, 2015 at 12:13:59PM -0400, Chris Mason wrote:
> > > > The issue is: under high CPU and disk I/O pressure, *some* processes can
> > suffer from a very slow write speed (e.g., <1MB/s or even only 20KB/s), while
> > the normal write speed should be at least dozens of MB/s.
> >
> > So, I think I know what caused this regression.  Separate wb domains
> > shouldn't have been enabled on traditional hierarchies.  It doesn't
> > work there and leads to multiple wb domains competing on the same
> > blkcg and the bw estimation would go completely haywire.  Will update
> > soon.
> >
> > Thanks.
> >
> > --
> > tejun
> 
> Thanks a lot for the quick fix, Tejun!
> 
> I'll test the fix.
> I'll report back in case it can't fix the issue --I think this is unlikely. :-)
> 
> -- Dexuan

Hi Tejun,
Thank you!
I believe your patch fixes my issue, according to my test.

-- Dexuan