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Re: Deleting files with extended attributes is dead slow

To: Bernd Schubert <bernd.schubert@xxxxxxxxxxxxxxxxxx>
Subject: Re: Deleting files with extended attributes is dead slow
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Wed, 17 Aug 2011 13:02:52 -0400
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>, linux-xfs@xxxxxxxxxxx
In-reply-to: <4E4BBC98.7020501@xxxxxxxxxxxxxxxxxx>
References: <j23qs9$1c3$1@xxxxxxxxxxxxxxx> <20110812204746.GB30615@xxxxxxxxxxxxx> <20110816161357.GA18201@xxxxxxxxxxxxx> <4E4BBC98.7020501@xxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Wed, Aug 17, 2011 at 03:05:28PM +0200, Bernd Schubert wrote:
> >(squeeze-x86_64)fslab2:~# xfs_bmap -a 
> >/mnt/xfs/Bonnie.29243/00000/00000027faJxifNb0n
> >/mnt/xfs/Bonnie.29243/00000/00000027faJxifNb0n:
> >        0: [0..7]: 92304..92311
> 
> (Sorry, I have no idea what "0: [0..7]: 92304..9231" is supposed to
> tell me).

It means that you are having an extent spanning 8 blocks for xattr
storage, that map to physical blocks 92304 to 9231 in the filesystem.

It sounds to me like your workload has a lot more than 256 bytes of
xattrs, or the underlying code is doing something rather stupid.

> Looking at 'top' and 'iostat -x' outout, I noticed we are actually
> not limited by io to disk, but CPU bound. If you should be
> interested, I have attached 'perf record -g' and 'perf report -g'
> outout, of the bonnie file create (create + fsetfattr() ) phase.

It's mostly spending a lot of time on copying things into the CIL
buffers, which is expected and intentional as that allows for additional
parallelity.  I you'd switch the workload to multiple intances doing
the create in parallel you should be able to scale to better numbers.

> >     100:256:256/10 37026  91 +++++ +++ 43691  93 35960  92 +++++ +++ 40708  
> > 92
> >Latency              4328us     765us    2960us     527us     440us    1075us
> >1.96,1.96,fslab2,1,1313594619,,,,,,,,,,,,,,100,256,256,,10,37026,91,+++++,+++,43691,93,35960,92,+++++,+++,40708,92,,,,,,,4328us,765us,2960us,527us,440us,1075us
> 
> 
> xfs:
> mkfs.xfs -f -i size=512 -i maxpct=90  -l lazy-count=1 -n size=64k /dev/sdd

Do 64k dir blocks actually help you with the workload?  They also tend
to do a lot of useless memcpys in their current form, although these
didn't show up on your profile.  Did you try using a larger inode size
as suggested in my previous mail?

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