Linux AS 3 server memory -whodunit

[Rick Stevens]

On Sun, 2006-02-26 at 15:09 +0530, mac wrote:
>  
>  
> Hi All,
>  
> We have a Linux AS server with 4 GB of RAM and problems (
> At any point of time my Free -m  Gives total of 4000 mb and used of
> 3900 and free 10 mb  but my buffers/cache used is hardly 1000 mb and
> 3000 mb free
>    
>   Whereas
>    
>    the top always gives 
>    
>   mem used 4000 mb avg and used 3972  
>    
>   Going by bufffers/cache i shudnt be having memory issues BUT our
> server is monitored and keeps throwing above 80% memory utilisation
> all the time
>    
>    
>   why is there a discrepancy between TOP and FREE and which shud be
> used more definitely for memory analysis

"top", "free" and "vmstat" use the same info from /proc.  That data is a
snapshot of what the memory was at the time the command read /proc.
Since top reads it once per update period, it will reflect the ongoing
state of memory, whereas free is a one-time look.  I prefer vmstat
myself and I can run make it run once ever "N" seconds for "X" loops.
   
>   and why do we get over 80% used all the time when buffers/cache is
> low all times

High memory utilization is a good thing.  It means the system is trying
to cache as much as it can.  The system doesn't split memory up...it
just uses what it has.  The other data ("buffers, cache, swap") just
show you where the memory is being used so you can do some tuning.

The only other option is using swap and that will slow your machine down
a LOT.  That's another place where vmstat can help you out--if you see
the "si" or "so" getting large, you need more RAM.

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- Rick Stevens, Senior Systems Engineer     rstevens at vitalstream.com -
- VitalStream, Inc.                       http://www.vitalstream.com -
-                                                                    -
-                       When in doubt, mumble.                       -
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