Swap issues with Linux 2.4.20-xx - Caching is causing unnecessary swaping

Jim Laverty jim at wangtrading.com
Fri Jan 30 15:01:01 CST 2004


Excellent information!  I'm pulling the patch down now.

I have been tweaking and tesing /proc settings, plus reading kernel code all
day.  

-----Original Message-----
From: Wolfgang Baudler [mailto:wbaudler at gb.nrao.edu] 
Sent: Friday, January 30, 2004 3:58 PM
To: jim at wangtrading.com; linux-poweredge at dell.com
Subject: Re: Swap issues with Linux 2.4.20-xx - Caching is causing
unnecessary swaping


Jim Laverty wrote:
> This is not a Dell specific question/issue, however the results are
similar
> to the hanging issues being brought up.   So far everyone I have spoken to
> has not noticed this, until we mentioned it and asked them to check 
> their servers.  Has anyone run into this issue below and found a 
> reasonable way to fix it, without disabling swap?
> 
> Since we have switched from the 2.4.18-xx kernels to the 2.4.20-xx 
> kernels, we have noticed that servers which do a lot of NFS traffic 
> are chewing up the cache and causing the system to swap even though 
> the apps are not using that much memory.  What happens is that the 
> system starts to swap and eventually comes to a crawl, since the 
> 'cached' data never seems to get freed.  This may not be limited to 
> NFS only, however that is where most of the testing has been done.
> 
> 

We had similar problems on all our machines that have more then 1GB of
memory. Any of the Redhat 2.4.20 or stock 2.4.20 kernels should this
misbehaviour.

The solution is to either disable the extra memory (mem=1024M boot option)
or 
to compile a kernel with the aa1 patches installed. 2.4.23aa1 works fine in 
this respect.

The patch is available for example at

http://www.us.kernel.org/pub/linux/kernel/people/andrea/kernels/v2.4/2.4.23a
a1.gz

This patch also applied clean against the 2.4.24 kernel.

Wolfgang
( happily running a DELL PE 8450 with 8GB of RAM now...)





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