Re: [PATCH] bump up nr_to_write in xfs_vm_writepage

From: Michael Monnerie <michael.monnerie@is.it-management.at>
To: xfs@oss.sgi.com
Subject: Re: [PATCH] bump up nr_to_write in xfs_vm_writepage
Date: Sat, 4 Jul 2009 01:51:19 +0200	[thread overview]
Message-ID: <200907040151.21013@zmi.at> (raw)
In-Reply-To: <4A4D26C5.9070606@redhat.com>

On Donnerstag 02 Juli 2009 Eric Sandeen wrote:
> With the following change things get moving again for xfs:

Amazeing, more than double speed with a one-liner. Do you have more such 
lines? ;-)

> +	/*
> +	 *  VM calculation for nr_to_write seems off.  Bump it way
> +	 *  up, this gets simple streaming writes zippy again.
> +	 */
> +	wbc->nr_to_write *= 4;

Could this be helpful here also: I've just transfered a copy of a 
directory from our server to a Linux desktop. Nothing else running, just 
an rsync from server to client, where the client has a Seagate 1TB ES.2 
SATA disk, whhic can do about 80MB/s on large writes. But it did this, 
measured on large files (>20MB each, no small files):

Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s avgrq-
sz avgqu-sz   await  svctm  %util
sdb               0,00   584,00    0,00  368,00     0,00  7448,00    
40,48   148,64  401,40   2,72 100,00

All the time around 300+ IOps, which is OK, but only 7-10MB/s? That 
can't be true. Then I killed the rsync process on the server, and the 
writes on the client jumped up:

sdb               0,00  4543,40    0,00  333,40     0,00 44965,60   
269,74   144,66  384,98   3,00 100,00

45MB/s is OK. I investigated a bit further: Seems the /proc/sys/vm 
values are strange, clients kernel is # uname -a
Linux saturn 2.6.30-ZMI #1 SMP PREEMPT Wed Jun 10 20:07:31 CEST 2009 
x86_64 x86_64 x86_64 GNU/Linux

This makes rsync slow:
cat /proc/sys/vm/dirty_*       
0                                       
5                                       
0                                       
8000                                    
50                                      
100                    

This fast:
cat /proc/sys/vm/dirty_*       
cat dirty_*
16123456
0
524123456
8000
0
100

Seems more like a kernel related stuff, but do others see the same 
thing?

So, I'm really out for a 1 week vacation now, have fun!

mfg zmi
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