Swap partition size (future proofing)

[Thomas Cameron]

----- Original Message ----- 
From: "David Fletcher" <fm_maillists at ntlworld.com>
To: <fedora-list at redhat.com>
Sent: Tuesday, February 01, 2005 2:22 AM
Subject: Swap partition size (future proofing)


>
> I've just ordered the parts to build a new PC :)
>
> The motherboard (Intel D865PERL) has four memory module sockets which can 
> take
> a total of 4G RAM.
>
> I have ordered a single 1G memory module, leaving me plenty of scope to 
> expand
> the memory later if I want to.
>
> Searching the Fedora List archive, I found various suggestions for
> increasing swap space by either adding a partion if there is unused space 
> on
> the HDD or using mkswap to create a swap file in an existing partition. 
> Hard
> drive space is fairly cheap these days so I want to set it up "right first
> time" so that I don't have to mess about if (when) I add more memory 
> later.
>
> Suggested swap partition sizes from the archives range from the same size 
> as
> the RAM to twice the size of the RAM.
>
> Given that I'm going to start with 1G of RAM, but could (but maybe won't) 
> end
> up with 4G of RAM, I'm thinking that maybe 6G would be a sensible size for
> the swap partition.
>
> What do the members think?
>
> Thanks,
>
> Dave Fletcher

Dave -

The amount of swap you need can be determined by one thing:  How much memory 
are you going to use on a regular basis, and how much physical memory do you 
have?  How much more memory do you need than the amount of physical memory 
installed?

In other words, if you are going to be running a desktop PC, I can't imagine 
that you will regularly have more than 1GB of processes running which need 
physical memory.  For a desktop PC you will likely be running your window 
manager, some apps like a web browser, an office productivity suite, maybe a 
graphics program such as the GIMP, maybe you'll be running a compiler now 
and then, and you'll have the network stack loaded.  I don't see that you 
will come near the 1GB memory capacity you have.  You'll likely never touch 
swap, so you don't really need a big, wasteful swap file.

Now if you were running a compute server, where numerous people were logged 
in concurrently and all of them were running big compiles or 
memory-intensive programs, then I could see that it might be realistic to 
expect that more than 1GB of memory is going to need to be used at the same 
time.  You might have more stuff going on than you have physical memory, and 
you'd want a healthy swap file.

In my case (and I have exactly the same motherboard, BTW), I am ruuning the 
motherboard in a lightly loaded web/mail/dns/ftp server.  I have 2GB memory 
and a 1GB swap file.  I *never* touch swap - the machine simply doesn't have 
enough going on to ever need to page information out of physical memory to 
the swap file:

[thomas.cameron at mail ~]$ free
             total       used       free     shared    buffers     cached
Mem:       2075228    1843364     231864          0     281348     981732
-/+ buffers/cache:     580284    1494944
Swap:       917968          0     917968

So the real answer is:  what are you doing with the machine?

Thomas