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Re: definitions for /proc/fs/xfs/stat

To: Mark Seger <mjseger@xxxxxxxxx>
Subject: Re: definitions for /proc/fs/xfs/stat
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Mon, 17 Jun 2013 09:14:29 +1000
Cc: Nathan Scott <nathans@xxxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
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User-agent: Mutt/1.5.21 (2010-09-15)
On Sun, Jun 16, 2013 at 06:31:13PM -0400, Mark Seger wrote:
> >
> > There is no way that fallocate() of 1000x1k files should be causing
> > 450MB/s of IO for 5 seconds.
> 
> I agree and that's what has me puzzled as well.
> 
> > However, I still have no idea what you are running this test on - as
> > I asked in another email, can you provide some information about
> > the system your are seeing this problem on so we can try to work out
> > what might be causing this?
> >
> 
> sorry about that.  This is an HP box with 192GB RAM and 6 2-core
> hyperthreaded CPUs, running ubuntu/precise
> 
> segerm@az1-sw-object-0006:~$ uname -a
> Linux az1-sw-object-0006 2.6.38-16-server #68hf1026116v20120926-Ubuntu SMP
> Wed Sep 26 14:34:13 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux

So it running a pretty old Ubuntu something-or-other kernel. There's
only limited help I can give you for this kernel as I've got no idea
what Ubuntu have put in it...

> segerm@az1-sw-object-0006:~$ python --version
> Python 2.7.1+
> 
> segerm@az1-sw-object-0006:~$ xfs_repair -V
> xfs_repair version 3.1.4
> 
> segerm@az1-sw-object-0006:~$ cat /proc/meminfo
> MemTotal:       198191696 kB
> MemFree:        166202324 kB
> Buffers:          193268 kB
> Cached:         21595332 kB
....
> over 60 mounts, but here's the one I'm writing to:
> 
> segerm@az1-sw-object-0006:~$ mount | grep disk0
> /dev/sdc1 on /srv/node/disk0 type xfs (rw,nobarrier)
> 
> not sure what you're looking for here so here's it all
> 
> segerm@az1-sw-object-0006:~$ cat /proc/partitions
> major minor  #blocks  name
> 
>    8        0  976762584 sda
>    8        1     248976 sda1
>    8        2          1 sda2
>    8        5  976510993 sda5
>  251        0   41943040 dm-0
>  251        1    8785920 dm-1
>  251        2    2928640 dm-2
>    8       16  976762584 sdb
>    8       17  976760832 sdb1
>  251        3  126889984 dm-3
>  251        4     389120 dm-4
>  251        5   41943040 dm-5
>    8       32 2930233816 sdc
>    8       33 2930233344 sdc1
....

> segerm@az1-sw-object-0006:~$ xfs_info /srv/node/disk0
> meta-data=/dev/sdc1              isize=1024   agcount=32, agsize=22892416
> blks
>          =                       sectsz=512   attr=2
> data     =                       bsize=4096   blocks=732557312, imaxpct=5
>          =                       sunit=64     swidth=64 blks
> naming   =version 2              bsize=4096   ascii-ci=0
> log      =internal               bsize=4096   blocks=357696, version=2
>          =                       sectsz=512   sunit=64 blks, lazy-count=1
> realtime =none                   extsz=4096   blocks=0, rtextents=0

Ok, that's interesting - a 1k inode size, and sunit=swidth=256k. But
it doesn't cause a current kernel to reproduce the behaviour you are
seeing....

sunit=256k is interesting, because:

>     0.067874 cpu=0 pid=41977 fallocate [285] entry fd=15 mode=0x1
> offset=0x0 len=10240
>     0.067980 cpu=0 pid=41977 block_rq_insert dev_t=0x04100030 wr=write
> flags=SYNC sector=0xaec11a00 len=262144

That's a write which is rounded up to 256k.

BTW, that's a trace for a also a 10k fallocate, not 1k, but
regardless it doesn't change behaviour on my TOT test kernel.

> I hope this helps but if there's any more I can provide I'll be
> happy to do so.

It doesn't tell me what XFS is doing with the fallocate call.
Providing the trace-cmd trace output from the FAQ might shed some
light on it...

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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