linux-kernel - Re: [PATCH 00/17] [RFC] soft and dynamic dirty throttling limits

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Message-ID: <20101013092627.GY4681@dastard>
Date:	Wed, 13 Oct 2010 20:26:27 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Theodore Ts'o <tytso@....edu>, Jan Kara <jack@...e.cz>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mel Gorman <mel@....ul.ie>, Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Chris Mason <chris.mason@...cle.com>,
	Christoph Hellwig <hch@....de>,
	"Li, Shaohua" <shaohua.li@...el.com>
Subject: Re: [PATCH 00/17] [RFC] soft and dynamic dirty throttling limits

On Wed, Oct 13, 2010 at 04:26:12PM +0800, Wu Fengguang wrote:
> On Wed, Oct 13, 2010 at 11:07:33AM +0800, Dave Chinner wrote:
> > On Tue, Oct 12, 2010 at 10:17:16AM -0400, Christoph Hellwig wrote:
> > > Wu, what's the state of this series?  It looks like we'll need it
> > > rather sooner than later - try to get at least the preparations in
> > > ASAP would be really helpful.
> > 
> > Not ready in it's current form. This load (creating millions of 1
> > byte files in parallel):
> > 
> > $ /usr/bin/time ./fs_mark -D 10000 -S0 -n 100000 -s 1 -L 63 \
> > > -d /mnt/scratch/0 -d /mnt/scratch/1 \
> > > -d /mnt/scratch/2 -d /mnt/scratch/3 \
> > > -d /mnt/scratch/4 -d /mnt/scratch/5 \
> > > -d /mnt/scratch/6 -d /mnt/scratch/7
> > 
> > Locks up all the fs_mark processes spinning in traces like the
> > following and no further progress is made when the inode cache
> > fills memory.
> 
> I reproduced the problem on a 6G/8p 2-socket 11-disk box.
> 
> The root cause is, pageout() is somehow called with low scan priority,
> which deserves more investigation.
> 
> The direct cause is, balance_dirty_pages() then keeps nr_dirty too low,
> which can be improved easily by not pushing down the soft dirty limit
> to less than 1-second worth of dirty pages.
> 
> My test box has two nodes, and their memory usage are rather unbalanced:
> (Dave, maybe you have NUMA setup too?)

No, I'm running the test in a single node VM.

FYI, I'm running the test on XFS (16TB 12 disk RAID0 stripe), using
the mount options "inode64,nobarrier,logbsize=262144,delaylog".

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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