new memory = more swap?

Jeff Lasman blists at nobaloney.net
Mon Mar 29 21:46:00 UTC 2004


On Thursday 25 March 2004 11:09 am, Matt Morgan wrote:

> Is it still also true, though, that swap should at a minimum = RAM
> (this is knowledge that dates back to early versions of SCO, which
> was weird anyway, I know)? If so, then having more swap than RAM may
> be worthwhile anyway, because you probably have plenty of disk space,
> and you might add RAM later (and you won't have to repartition at
> that point if you have extra swap).

Matt,

I passed your question on to a fairly technical linux list, the linux 
list at the University of Florida, and got a response from a gent who's 
probably fairly knowledgeable (http://www.tech9.net/rml/); he wrote:

<snip>
It used to be the case (early 2.4 series) that swap had to be twice
physical RAM.  That limitation has since been removed and swap can be
any size.
</snip>

I also asked him if the linux kernel dumps memory to swap in the event 
of a panic.  I wrote:

> Having used SCO xenix and unix back in the days when SCO was a real
> company, I recall the reason was because in case of a panic the kernel
> would attempt to dump memory to swap space for later examination.
>
> Does anyone know if the linux kernel does that or ever did?

His response:

<snip>
Nope, never did.
</snip>

I also got back another response (from a second gent) to your question 
as to whether swap should at least equal memory, and got back:

<snip>
This is a throwback to operating systems that required that every page
of ram have a page of swap tied to it.  That guideline has been obsolete
for at least 10 years.
</snip>

You also asked:

> Can you have too much swap? (Disk space issues aside). If I have 512
> Mb of RAM, and set up a 1Gb swap partition, did I make a mistake?

And in response the same (second) gent also wrote:

<snip>
You should set your swap so that RAM+swap = max memory you expect to
use.  Of course, that's hard to predict.  On the other hand, you have to
make sure to set your swap low enough that when you're just running too
many programs the operating system will kill them, rather than enter
thrashing hell.  It's a judgement call.
</snip>

I think we've gotten some good advice here <smile>.  I'm going to go 
with it.

Jeff
-- 
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