Subject: Re: slow performance on disk/network i/o full speed after drop_caches

From: Wu Fengguang <[email-masked]>
Date: Fri, 26 Aug 2011 11:26:02 +0800

On Fri, Aug 26, 2011 at 11:13:07AM +0800, Stefan Priebe wrote:
> 
> >> There is at least a numastat proc file.
> > 
> > Thanks. This shows that node0 is accessed 10x more than node1.
> 
> What can i do to prevent this or isn't this normal when a machine mostly idles so processes are mostly processed by cpu0.

Yes, that's normal. However it should explain why it's slow even when
there are lots of free pages _globally_.

> > 
> >> complete ps output:
> >> http://pastebin.com/raw.php?i=b948svzN
> > 
> > In that log, scp happens to be in R state and also no other tasks in D
> > state. Would you retry in the hope of catching some stucked state?
> Sadly not as the sysrq trigger has rebootet the machine and it will now run fine for 1 or 2 days.

Oops, sorry! It might be possible to reproduce the issue by manually
eating all of the memory with sparse file data:

        truncate -s 1T 1T
        cp 1T /dev/null

> > 
> >>>         echo t>  /proc/sysrq-trigger
> >> sadly i wa sonly able to grab the output in this crazy format:
> >> http://pastebin.com/raw.php?i=MBXvvyH1
> > 
> > It's pretty readable dmesg, except that the data is incomplete and
> > there are nothing valuable in the uploaded portion..
> That was everything i could grab through netconsole. Is there a better way?

netconsole is enough.  The partial output should be due to the reboot...

Thanks,
Fengguang

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