-----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 [off-list ref]; Andreas Dilger [off-list ref];
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:

quoted

quoted

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