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Old 03-25-2007, 10:45 AM   #1
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ram and swap usage?

Hello all,

I have a production server based on RedHat 4 with 2 xeon cpu and 16 GIGs ram.

According to RedHat's guide I have set up nine swap unit of 2 GIGs (18 GIGs total of swap).

On this server runs 3 instances of oracle 9i of 2 GIGs of SGA for instance. (6 GIGs of sga).

Kernel is hugememory smp 2.6.9 and I've set shmmax as 3 GIGs, and swappiness value as 30.

When I check ram utilizzation with free command I say that about 3/400 MB of swap is always used and there is about 12 GIGs of buffer free...

# free -m
total used free
Mem: 16202 16180 22
-/+ buffers/cache: 3480 12275
Swap: 18437 384 18053

What do you think about? is it okay, or what? Do I have to do more tuning?

Thank you
Old 03-25-2007, 12:24 PM   #2
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FredericV, are you a long time Windows admin/user? Linux is actually 'intelligent' when it comes to memory management and will make every attempt to NOT USE swap for memory transactions.
Old 03-25-2007, 12:36 PM   #3
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I know... so, why my system is swapping? I thought that it doesn't need to use swap...
Old 03-25-2007, 01:23 PM   #4
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Your system isn't doing much swapping at all
Swap: 18437 (<-total) 384 (<-used) 18053(<-free)
In other words, you are only actually using about 2% of your swap space
Old 03-25-2007, 03:10 PM   #5
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yes, it's a very small swap usage, but, why using swap when it has 12 GIGs of ram free?
Do you think that I have to reduce swap size or swappiness? or is it almost ok?
Old 03-25-2007, 03:17 PM   #6
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I sometimes have a few KB showing on my swap space, but there's no reason to suspect my machine is swapping. I simply don't have processes running that would need it. But, as to swap space; we've argued incessantly over this, and I hate to get into it again. But, here's the deal: you need enough memory to run your processes. That memory can either be RAM only or it can be a combination of RAM and swap. Ask yourself how much user plus kernel memory space you need to run everything at once. If you need 34GB of total memory footprint, then you're fine. If not, well, what would you gain by messing with something that's clearly working OK?

Beware of informationitis. Just because you know something doesn't necessarily mean you need to do something about it.
Old 03-25-2007, 04:56 PM   #7
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Originally Posted by FredericV
and there is about 12 GIGs of buffer free...
That isn't what it is saying at all.
If cache/buffers (the relevant output of which you deleted) were not in use, that's how much extra free memory you'd have. As your applications are not demanding it, it's used more productively.
Would you rather you'd paid for that 12 Gig and never use it ???.
Same for the swap usage. Long term idle anonymous memory pages are pushed out so the RAM they occupy can be used elsewhere.

What's your uptime ???.
(In future use code tags to make your data readable)

Edit: D'oh - left out the emphasised "not" above.

Last edited by syg00; 03-25-2007 at 05:01 PM.


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