CentOS - Sep 2006 - kbcached tuning on CentOS 4

Hello,

 

I've been searching to no end at how to tune at what interval (or size)
kbcached will be flushed.

 

I had been chasing a potential memory leak until "sar -r", had
revealed
that all the "mysteriously used" memory was actually being taken up by
the kernel data cache.  It is chewing up all unused memory on the system
slowly over time, which is a concern.  Various sources have pointed me
towards making modification in the /proc/sys/vm file-system although
kernel documentation on the files within doesn't seem to really fit what
I'm trying to do.

 

Any way to set the kbcached buffer to be flushed either at a specified
time interval or once it hits a certain size would be a great help.

 

Thoughts anyone?

 

Thanks,

 

Justin Randall

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On Fri, 2006-09-08 at 10:31 -0400, Justin Randall wrote:
> I had been chasing a potential memory leak until ?sar ?r?, had
> revealed that all the ?mysteriously used? memory was actually being
> taken up by the kernel data cache.  It is chewing up all unused memory
> on the system slowly over time, which is a concern.
Why is this a concern? The larger a cache is, the more potential cache
hits. Linux is pretty smart about managing caches and buffers, and will
grow/shrink the cache depending on the amount of memory.

-- Daniel

Thanks for the response.

The real concern comes from administrators or other less technical staff
logging into the box, and getting concerned at the amount of memory used
up.  Although user education is always positively accepted, the general
comfort level would be much higher if they could login to a host and not
see that 98% of memory is in use.

Regarding performance, this isn't much of a concern, although this host
is intermittently hit with large work loads (which is why the kernel
cache reaches the point of consuming all memory) which consume much
memory, and another thought was that when these sporadic work loads
proceed, there would be a slight performance hit waiting for free memory
to be available as the cache is cleared.

If this thought is misguided please let me know.  Either way, what would
be the correct method for tuning the kernel parameters?

Justin.

-----Original Message-----
From: Daniel de Kok [mailto:danieldk at pobox.com] 
Sent: Monday, September 11, 2006 10:36 AM
To: CentOS mailing list
Subject: Re: [CentOS] kbcached tuning on CentOS 4

On Fri, 2006-09-08 at 10:31 -0400, Justin Randall wrote:
> I had been chasing a potential memory leak until "sar -r", had
> revealed that all the "mysteriously used" memory was actually
being
> taken up by the kernel data cache.  It is chewing up all unused memory
> on the system slowly over time, which is a concern.
Why is this a concern? The larger a cache is, the more potential cache
hits. Linux is pretty smart about managing caches and buffers, and will
grow/shrink the cache depending on the amount of memory.

-- Daniel

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Howdy,

This is a good read for anyone interested in the memory handling of RHEL4:

   http://people.redhat.com/nhorman/papers/rhel4_vm.pdf

robert