new memory = more swap?

[Tom Needs a Hat Mitchell]

On Sat, Mar 13, 2004 at 04:58:45PM +0200, Maynard Kuona wrote:
> Reply-To: For users of Fedora Core releases <fedora-list at redhat.com>
> 
> On Sat, 2004-03-13 at 16:44, Craig Thomas wrote:
> > I have 256MB ram and a 502MB swap, and want to increase to 384MB ram, [i
> > know, i know it's an old machine].  I've read in the RH manual and else
> > where that double the amount of ram is "right".  If I want more swap but
> > don't have any unpartitioned space left, what are my options?  (I do,
> > however, have lots of free space on my drive).
> 
....
> have is a rule of thumb. If you do not expect to be swapping much, i.e.,
> you are not doing any intensive graphics work, then you will hardly use
> your swap anyway. From my experience, I have rarely needed the swap
> partition.
....

Craig,

Do nothing different for now.

Since you have more DRAM you will need to swap less not more ;-)

If you later find you need more swap space you can add a "swap to file" swap
resource as disk space permits (swap + swap_file=total_swap;
total_swap+DRAM=total_VM).

The advantage of a modest swap partition and later adding swap files
is that a big unused swap space on disk is wasteful.  Swap files can
be added or removed as needed without repartitioning the disk.

Since you have the disk space -- you can try swap to files.
Note that additions can be done without a reboot.

Swap IO to disk is so slow in comparison to DRAM that swap is 
painful.  Over the years the rules of thumb have shifted from +4xRAM
to ~1x RAM or less.  The reason is that processors are +1000 fold
faster but disks keep on spinning close to the older rates.

Big computational server configurations with multiple GB of RAM and TB
of disk and tape have other issues.

To understand the 2x rule Google search about for "virtual memory",
fork(), exec(), "copy on write".   I think 2x is still a good rule for
building a new box.


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