To swap or not to swap that is the question

[David Kramer]

On Monday 07 October 2002 04:06 pm, ron.peterson at yellowbank.com wrote:
> On Mon, Oct 07, 2002 at 03:05:01PM -0400, Jerry Feldman wrote:
> > The old rule of thumb was 3 X memory.
>
> Or 2x, or 2.5x...
>
> I believe early 2.4 kernels required an amount of swap equal to ram
> *before* you began to increase the size of your VM.  So if your swap was
> 2x your RAM, your VM would be 2x your RAM.  So if you wanted swap to be
> double your RAM (the old rule of thumb) you'd need swap to be 3x your
> RAM.
>
> I'm just blowing smoke in a feeble attempt to grok where these 'rules of
> thumb' come from.

It is my understanding that in earlier kernels, a core dump would create an 
exact copy of the entirety of physical RAM.  You needed twice the swap space 
as physical RAM so you were guaranteed enough space for all running apps to 
swap out as needed, and to create the big honkin' core file, which was the 
size of the physical RAM.

I believe the current kernels do not function this way anymore, and core files 
are much smaller, so there is no need for that extreme.
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