From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754423AbbIWSxn (ORCPT ); Wed, 23 Sep 2015 14:53:43 -0400 Received: from mail-yk0-f174.google.com ([209.85.160.174]:35095 "EHLO mail-yk0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751723AbbIWSxm (ORCPT ); Wed, 23 Sep 2015 14:53:42 -0400 Date: Wed, 23 Sep 2015 14:53:37 -0400 From: Tejun Heo To: Chris Mason , Dexuan Cui , "Theodore Ts'o" , Andreas Dilger , "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 Message-ID: <20150923185337.GK26647@mtj.duckdns.org> References: <20150923161359.GB25218@ret.masoncoding.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150923161359.GB25218@ret.masoncoding.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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