Swap size

[WipeOut]

T. Ribbrock wrote:

>On Wed, Jan 28, 2004 at 03:28:19PM +0000, WipeOut wrote:
>  
>
>>My only real comment is on the swap allocation.. I think the 2 X RAM is 
>>old school thinking from back in the day when RAM was expensive and a 
>>highend server had 128MB of it.. If your system ever needs to used more 
>>than about 128 - 256MB of swap space then you seriously need to a) add 
>>more RAM or b) offload some of the services on the server to another..
>>    
>>
>
>Actually, the whole swap story is a strange one as far as I've seen
>it... In the time of kernel 2.0.x, it was indeed advised to have 2xRAM
>as a minimum, just for the reasons you mentioned. Later, with 2.2.x,
>most people agreed that "RAM+swap" should just be enough to cater for
>the maximum of memory usage you expect to see, ever. That's when I
>switched to 1xRAM.
>
>However, then 2.4.x came and suddenly, everybody suggested 2xRAM again.
>I remember reading about it and there was some reasoning behind it, but
>I don't know the details. If someone can shed some light on this, I'd
>appreciate it.
>
>  
>
That is interesting.. I still think its more of a guideline.. Think of 
the following senario..

Server with 2GB of RAM, using the 2x RAM rule would mean 4GB of swap 
space.. To my mind this means the server would have to address 6GB or 
memory and so would probably need , I asume, the "bigmem" kernel in 
order to manage the RAM properly and from what I have read the "bigmem" 
kernel has an overhead to system performance of about 6-10%.. Add to 
that the "slowness" of hard drives it really does not sit well with me..

There probably is no "correct" answer I think its would be up to the 
Admin for the most part as to how the system needed to run.. Pesonally I 
would rather have my system working out of RAM than having hundreds or 
thousands of MB of "slow memory".. :)

later..