SWAP Question?

Roy Sigurd Karlsbakk roy at karlsbakk.net
Wed Aug 12 09:19:29 UTC 2009


On 10. aug.. 2009, at 23.28, Michael S. Mason wrote:

> Hello All,
>
> My name is Michael,
>
> I have a new Dell Server that I am about to install Ubuntu 9.04 Server
> AMD64 onto. I have 4 GB's of RAM. My question? Is there any need for a
> SWAP partition with 4GB's of RAM?


Hi

I see you have gotten a few answers from others, mostly saying "you  
don't need swap" or similar.

Given the fact that memory requirements increase while available  
memory increases, although the availability may rise quicker, the old  
thumb of rule is still a good one: Use memory size as a base for swap  
size and make the swap 1-2x memory size. Swap used to be a last effort  
in case of (almost) full memory. Newer methods of swapping mechanisms,  
such as those in recent Linux kernels, have changed this. Setting the  
sysctl vm.swappiness variable to 100 makes Linux start swapping out  
earlier, which is good for most systems. Swapping out memory not  
currently in use (that is, malloc()ed and written to and forgotten) is  
good, since it means the system can use its memory for something  
useful, such as caching. Disabling swap altogether is not recommended,  
since a standard linux build relies on swap. You can build a linux  
kernel without swap support, but I don't really see the point.

My advice: with 4 gigs of memory, make a swap partition of 4 gigs,  
perhaps more if you're paranoid. Disk space are so cheap these days,  
that space will cost you less than a dollar. Also - set vm.swappiness  
= 100 in /etc/sysctl.conf (that is /proc/sys/vm/swappiness) to make  
Linux start swapping out early. It will just swap out all those pages  
not regularly referenced, which is good.

roy
--
Roy Sigurd Karlsbakk
(+47) 97542685
roy at karlsbakk.net
http://blogg.karlsbakk.net/
--
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