Re: High CPU load with kswapd and heavy disk I/O

[Nuno Silva <nuno.silva@vgertech.com>]

Hi!

Ken Savage wrote:
> On Tue August 12 2003 16:49, Nuno Silva wrote:
> 
> 
>>My guess is that this is the cause. LOWMEM pressure because of very
>>large directories... Relating to this, linux-2.6.0-test3-mm1 has Ingo's
>>4G/4G memory split. Can you try this kernel, enable 4G/4G feature, and
>>report back?
> 
> 
> Something about the 2.6 (and the rmap patched 2.4) kernels causes
> lockouts on the server -- for reasons OTHER than kswapd.  The server

If you want to help, you could try to gather more info on that to help 
develope a better 2.6 ;)

FWIW, 2.6.0-test* with mm patches works well here... At least in a few 
boxes.


> running the delete-old-files process runs hundreds of other CPU and disk
> I/O intensive processes/threads, and it doesn't look like 2.6 is yet able
> to handle the load.  Unfortunately, the server is a production environment
> machine at a remote site, so lockouts/reboots/kernel panics are baaaad :(
> 
> I've seen other mentions of kswapd/kupdated problems in 2.4.xx, but
> few mentions of solutions.  Have people just learned to avoid the
> situations that trigger the mad thrashes?
> 


If you're sure that it's really kswapd you can send SIGSTOP and SIGCONT 
to kswapd's pid. Kswapd will honor those signals.

killall -STOP kswapd
<run your I/O intensive scripts>
killall -CONT kswapd

Sometimes I do this... For me it works well. If this makes your machine 
crash or loose data, don't blame me! ;)

Regards,
Nuno Silva


> Ken
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