Swap space

[Mark Lane]

On Sun, Dec 13, 2009 at 2:05 PM, William Muriithi <
william.muriithi-Re5JQEeQqe8AvxtiuMwx3w at public.gmane.org> wrote:

> Robert,
>
> 2009/12/12 Robert Brockway <robert-5LEc/6Zm6xCUd8a0hrldnti2O/JbrIOy at public.gmane.org>:
> > On Fri, 11 Dec 2009, William Muriithi wrote:
> >
> >> 2 GB is the maximum Linux kernel will ever use. Anything above that
> >> will never be used however loaded the system is
> >
> > Hi William.  There is a limit to swap that a modern Linux system can use
> but
> > it is too big for anyone to care.  On a quick search the figure of 4TB
> was
> > mentioned on LKML.
> >
> > There was a 2GB limit _per swap space_ but even that has been gone for
> quite
> > some time, and in any case it was easy to work around that by using
> multiple
> > swap spaces.
>
> Thanks Robert. Now that I have looked at it again, I see where I got
> the 2GB limit. You need to create multiple swap space to go above the
> 2GB.
>
> > I regularly build systems with a single swap space larger than 2GB and
> they
> > work just fine.
>
> Ah, interesting. Any system that I have ever installed all have 2 GB,
> so we are in the same boat here. This discussion also triggered me to
> realise I have means to access if large swaps are necessary in real
> life. Every system at work is monitored through cacti. I just looked
> at some of the systems that are heavily used and arrived at two
> conclusions.
>
> * The more RAM you have, the less likely the system will use it even
> under a heavy load. Some of the 16 GB systems have NEVER used swap for
> over two years according to cacti. Would there be something else using
> cacti to confirm whether this is general or load specific. Most of our
> system are either web servers (apache  and nginx) or database ( mysql)
>
> * NONE of the system have ever used over 500 MB so far, irrespective
> of the load. Look like the 2 GB is actually a tad overkill
>
> Generally servers don't need as much swap because unlike a desktop you
aren't openning up a lot of applications. Sure your servers like apache can
open up lots of threads during load but additional threads is not the same
as starting up a whole new application like open office.


-- 
Mark Lane <lmlane-Re5JQEeQqe8AvxtiuMwx3w at public.gmane.org>
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