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Re: xfs: very slow after mount, very slow at umount

To: Mark Lord <kernel@xxxxxxxxxxxx>
Subject: Re: xfs: very slow after mount, very slow at umount
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Fri, 28 Jan 2011 10:41:52 +1100
Cc: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Alex Elder <aelder@xxxxxxx>, Linux Kernel <linux-kernel@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <4D418B57.1000501@xxxxxxxxxxxx>
References: <4D40C8D1.8090202@xxxxxxxxxxxx> <20110127033011.GH21311@dastard> <4D40EB2F.2050809@xxxxxxxxxxxx> <4D418B57.1000501@xxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Thu, Jan 27, 2011 at 10:12:23AM -0500, Mark Lord wrote:
> On 11-01-27 12:30 AM, Stan Hoeppner wrote:
> > Mark Lord put forth on 1/26/2011 9:49 PM:
> > 
> >> agcount=7453
> > 
> > That's probably a bit high Mark, and very possibly the cause of your 
> > problems.
> > :)  Unless the disk array backing this filesystem has something like 400-800
> > striped disk drives.  You said it's a single 2TB drive right?
> > 
> > The default agcount for a single drive filesystem is 4 allocation groups.  
> > For
> > mdraid (of any number of disks/configuration) it's 16 allocation groups.
> > 
> > Why/how did you end up with 7452 allocation groups?  That can definitely 
> > cause
> > some performance issues due to massively excessive head seeking, and 
> > possibly
> > all manner of weirdness.
> This is great info, exactly the kind of feedback I was hoping for!
> The filesystem is about a year old now, and I probably used agsize=nnnnn
> when creating it or something.
> So if this resulted in what you consider to be many MANY too MANY ags,
> then I can imagine the first new file write wanting to go out and read
> in all of the ag data to determine the "best fit" or something.
> Which might explain some of the delay.
> Once I get the new 2TB drive, I'll re-run mkfs.xfs and then copy everything
> over onto a fresh xfs filesystem.
> Can you recommend a good set of mkfs.xfs parameters to suit the 
> characteristics
> of this system? 


And perhaps you want to consider the allocsize mount option, though
that shouldn't be necessary for 2.6.38+...


Dave Chinner

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