[CentOS] CentOS 3 vs. CentOS 4 Memory Utilization

[chrism at imntv.com]

hkclark at gmail.com wrote:
> On 2/8/07, Johnny Hughes <mailing-lists at hughesjr.com> wrote:
>>
>> It should not be a problem as lots of your memory used is buffers and
>> cache.
>>
>> CentOS-3 is going to be supported for a while yet (EOL is scheduled for
>> Oct 31, 2010), so if it is working perfectly and doing what they want,
>> they may want to keep it though.
>>
>> If they upgrade or don't, the memory should be OK either way .
>>
>
> Hi Johnny,
>
> Good info -- thanks.  They have a small app they want to add that
> requires a newer version of Perl than 5.8.0 that comes with CentOS 3.
> Rather than getting into a non-RPM version of Perl, we were thinking
> going to CentOS 4 would be easier and cleaner.
>
> In your experience, would you say that my "quick & dirty" measurement
> of CentOS 4 needing 10-25 MB more memory than CentOS 3 (again, for a
> non-X box with a minimal install) is accurate (at least in approximate
> terms)?  Or is there something I'm not taking into account -- e.g,
> some of the libraries and/or other "basic server apps" such as apache
> with PHP or MySQL will make that number much higher?  Although this
> box is doing OK on memory now, I would hate to kill their possible
> expansion plans just because we did an upgrade and it sucked up way
> more memory than we though.
>
> Again, thanks for all the great things you and the CentOS team are doing!

Here is the output of "free" for 2 identical systems that happen to be 
running CentOS3 and CentOS4.  The only difference is the CentOS4 system 
has 2GB RAM vs 1GB in the CentOS3 system.

The CentOS3 system shows:

             total       used       free     shared    buffers     cached
Mem:       1024292     660572     363720          0     102612     397072
-/+ buffers/cache:     160888     863404
Swap:      2104464          0    2104464


CentOS4 shows:

             total       used       free     shared    buffers     cached
Mem:       2074928    2030412      44516          0     276628    1365792
-/+ buffers/cache:     387992    1686936
Swap:      2104464        144    2104320

As others have noted, a lot of the free RAM is just gobbled up as 
buffers and cache.  As needed, the system will reallocate that memory so 
that your fancy perl application can get at it.  :)

Call me crazy, but I don't understand the agonizing fork in the decision 
tree here.  RAM is ridiculously cheap.  Why not just upgrade to 1GB 
while you're doing the 3-->4 upgrade?  I suspect it isn't really needed, 
but it will add minimal cost to the operation (certainly much less than 
the cost of your time to accomplish the software update and test the new 
system).

Cheers,