Swap size
Andy Greenwood
greenwood.andy at gmail.com
Fri Aug 17 08:07:21 PDT 2007
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?
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