From: Dave Chinner Subject: Re: 3.2 and 3.1 filesystem scalability measurements Date: Wed, 1 Feb 2012 07:27:57 +1100 Message-ID: <20120131202757.GK9090@dastard> References: <4F261807.2060108@hp.com> <4F26B395.6020607@gmail.com> <20120131001415.GC9090@dastard> <20120131105353.GA1278@quack.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andreas Dilger , "aziro.linux.adm" , Eric Whitney , Ext4 Developers List , linux-fsdevel@vger.kernel.org To: Jan Kara Return-path: Content-Disposition: inline In-Reply-To: <20120131105353.GA1278@quack.suse.cz> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Tue, Jan 31, 2012 at 11:53:53AM +0100, Jan Kara wrote: > On Tue 31-01-12 11:14:15, Dave Chinner wrote: > > I also found this oddity on both XFS and ext4: > > > > flush-253:32-3400 [001] 1936151.384563: writeback_start: bdi 253:32: sb_dev 0:0 nr_pages=-898403 sync_mode=0 kupdate=0 range_cyclic=1 background=1 reason=background > > flush-253:32-3400 [005] 1936151.455845: writeback_start: bdi 253:32: sb_dev 0:0 nr_pages=-911663 sync_mode=0 kupdate=0 range_cyclic=1 background=1 reason=background > > flush-253:32-3400 [006] 1936151.596298: writeback_start: bdi 253:32: sb_dev 0:0 nr_pages=-931332 sync_mode=0 kupdate=0 range_cyclic=1 background=1 reason=background > > flush-253:32-3400 [006] 1936151.719074: writeback_start: bdi 253:32: sb_dev 0:0 nr_pages=-951001 sync_mode=0 kupdate=0 range_cyclic=1 background=1 reason=background > > > > That's indicating the work->nr_pages is starting extremely negative, > > which should not be the case. The highest I saw was around -2m. > > Something is not working right there, as writeback is supposed to > > terminate if work->nr_pages < 0.... > Ugh, what kernel is this? The tracepoint is just a couple of lines after > if (work->nr_pages <= 0) > break; > so I really don't see how that could happen. Neither can I - it is the latest Linus kernel (3.3-rc1+). I even upgraded trace-cmd to the latest in case that was the problem, but it didn't make any difference. I haven't worked it out yet. Cheers, Dave. -- Dave Chinner david@fromorbit.com