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LINUX-L  2007

LINUX-L 2007

Subject:

Re: My server uses swap :(

From:

Jon Lewis <[log in to unmask]>

Reply-To:

Platform Independent Linux List! <[log in to unmask]>

Date:

Sat, 10 Mar 2007 21:48:27 -0500

Content-Type:

TEXT/PLAIN

Parts/Attachments:

Parts/Attachments

TEXT/PLAIN (49 lines)

On Sat, 10 Mar 2007, Daniel Franke wrote:

> On Sun, Mar 11, 2007 at 12:39:41AM +0200, Arthur Sherman wrote:
>> I've 3GB RAM on my (hosting) server.
>> When I last checked with 'free', I realised that it had some KB of swap
>> used, while having >2GB of RAM unused:
>>
>> --
>> [root@ns1 mail]# free
>> total used free shared buffers cached
>> Mem: 3115152 969056 2146096 0 163456 303584
>> -/+ buffers/cache: 502016 2613136
>> Swap: 1052152 8 1052144
>> --
>>
>> I assume that there has been a peak in usage.
>> How do I check what app/site sucked the RAM?
>
> That's completely normal. The kernel will always try to use as much memory
> as it can spare for I/O buffering. If buffer memory gets heavily fragmented,
> it'll use a bit of swap space while it defragments. The performance impact
> is negligible and it'll happen no matter how much RAM you have. After the
> memory frees up, the swap space will remain in use because fetching from
> swap is done lazily (i.e. on-demand).

The odd thing I see above is 2GB of free. That means one of three things.

Either the system was recently rebooted and hasn't gotten around to using
2/3 of the available RAM.

Something did actually eat up a huge amount of RAM and recently freed it.

The system is relatively idle and has way more RAM than it needs.

Over time, you should see nearly all your "free" RAM end up in buffers +
cache.

i.e.

              total used free shared buffers cached
Mem: 4068148 4056360 11788 0 55484 2627704
-/+ buffers/cache: 1373172 2694976
Swap: 4184924 547152 3637772

----------------------------------------------------------------------
  Jon Lewis | I route
  Senior Network Engineer | therefore you are
  Atlantic Net |
_________ http://www.lewis.org/~jlewis/pgp for PGP public key_________

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