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Date:	Thu, 24 Sep 2015 00:15:37 +0000
From:	Dexuan Cui <>
To:	Tejun Heo <>, Chris Mason <>,
	Theodore Ts'o <>,
	Andreas Dilger <>,
	"" <>,
	"" <>,
	"" <>
Subject: RE: ext4: performance regression introduced by the cgroup writeback

> -----Original Message-----
> From: Tejun Heo [] On Behalf Of Tejun Heo
> Sent: Thursday, September 24, 2015 2:54
> To: Chris Mason <>; Dexuan Cui <>;
> Theodore Ts'o <>; Andreas Dilger <>;
>;; linux-
> 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
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