Swap space

William Muriithi william.muriithi-Re5JQEeQqe8AvxtiuMwx3w at public.gmane.org
Sun Dec 13 19:05:17 UTC 2009


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

William
> Cheers,
>
> Rob
>
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