linux-ext4 - Re: 3.2 and 3.1 filesystem scalability measurements

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Message-ID: <20120131105353.GA1278@quack.suse.cz>
Date:	Tue, 31 Jan 2012 11:53:53 +0100
From:	Jan Kara <jack@...e.cz>
To:	Dave Chinner <david@...morbit.com>
Cc:	Andreas Dilger <adilger@...ger.ca>,
	"aziro.linux.adm" <aziro.linux.adm@...il.com>,
	Eric Whitney <eric.whitney@...com>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: 3.2 and 3.1 filesystem scalability measurements

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.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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