Swap size

[Andy Greenwood]

Jerry McAllister wrote:
> On Fri, Aug 17, 2007 at 02:05:57AM +0200, Nicholas Wieland wrote:
>
>   
>> I was reading tuning(7), and I found that I should size my swap  
>> double the size of my physical memory.
>> AFAIK that was true some years ago, when memory was not as cheap as  
>> now, and following that guideline I should set my swap to 2GB, which  
>> seems far too much for swap (at least to me ...). I will never need  
>> this much memory as 1GB RAM and 2GB swap.
>> Is it still correct ? How can I resize with bsdlabel if I already  
>> used all my disk space during install ?
>>     
>
> Remember, disk sizes have shot up too.
> No, 2 GB is not excessive.   You can get by with less, but you're
> not likely to be using proportionately as much disk now as you used
> to by going with 2X - I aim for a little over 2X.
>
> Remember that swap gets used for crash dumps and also for paging.
> Now, you may think that you want to keep your machine from paging 
> and in one sense that is true.   If you are so memory bound that
> it has to page just to run, you're going to be so slow that it 
> seems to have froze (by today's standards).   But, the system does
> write stuff to page space and for processes that are often called
> it can speed things up.  
>
> So, it is not really a waste to assign that much to swap.
>
> ////jerry
>
>   
>> TIA,
>>   ngw
>>
>> -- 
>> Nicholas Wieland
>> nicholas.wieland at gmail.com
>>
>>
>>
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>   
My understanding was that you should estimate swap size based on the 
sizes of the programs which might be paged out. However, when I first 
set up my system, I didn't know this and created 1G swap slices (one on 
each disk) but I am not convinced that this was the best thing to do, 
since my system almost never uses a noticible percentage of the swap 
space. right now, I've got

[andy at zeus fusefs-sshfs]$ swapinfo
Device          1K-blocks     Used    Avail Capacity
/dev/ad0s1b.eli   1048576     1148  1047428     0%
/dev/ad1s1b.eli   1048576     1096  1047480     0%
Total             2097152     2244  2094908     0%

And the system is under normal load. This system has 1G of RAM. Is there 
any sense in having this much swap space when it's not being used?