linux-ext4 - Re: Severe slowdown caused by jbd2 process

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Date:	Fri, 21 Jan 2011 09:03:06 -0500
From:	Josef Bacik <josef@...hat.com>
To:	Josef Bacik <josef@...hat.com>
Cc:	Jon Leighton <j@...athanleighton.com>, linux-ext4@...r.kernel.org
Subject: Re: Severe slowdown caused by jbd2 process

On Fri, Jan 21, 2011 at 07:59:22AM -0500, Josef Bacik wrote:
> On Fri, Jan 21, 2011 at 09:11:23AM +0000, Jon Leighton wrote:
> > Hi Josef,
> > 
> > Thanks for the reply.
> > 
> > On Thu, 2011-01-20 at 20:31 -0500, Josef Bacik wrote:
> > > What kind of database is this?  Does it use lots of files?
> > 
> > This happens with all databases that I test with: sqlite3, mysql and
> > postgresql. Which would seem to indicate that the issue is not actually
> > related to the databases, but is being made evident by them when they do
> > lots of reads/writes. (The jbd2 every 2 seconds thing happens even when
> > all database are completely shut down.)
> >
> 
> Right I'm not trying to blame the database, more trying to get an idea the kind
> of IO that they are generating so we can figure out what is being slow.
>  
> > > When it's being
> > > particularly slow could you run
> > > 
> > > echo w > /proc/sysrq-trigger
> > > 
> > > a couple of times, spread out.  This will give us an idea of what everybody is
> > > doing when things are going slow.  Thanks,
> > 
> > Cool, I have done that and attached the results. The partition in
> > question (the one with the databases on) is /dev/sda4.
> >
> 
> Hrm so an fsync heavy workload it looks like.  I'll run some fsync tests locally
> and see if I can see the kind of slowdowns you are experiencing.  Thanks,
>

Heh so now that I've had a moment to wake up, how about running your test on
ext3, but mount the partition with

mount -o barrier

and see if it's still faster than ext4.  Thanks,

Josef 
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