[ILUG] Ram swap

[Michael Watterson]

Niall O Broin wrote:
> On 5 Aug 2008, at 16:50, Frank Peelo wrote:
>
>>> Going less than 1:1 (or even 1:0)  on most OS, that have LOTS of RAM 
>>> ought to be possible, but for Mortals with LOTS* of RAM the limit is 
>>> 1:1 unless you really really understand what you are doing.
>>
>> Is that an upper or a lower limit? i.e. is 1:1 the minimum amount of 
>> RAM or the minimum amount of swap?
>
> There was a time a while ago when the Linux kernel had a bug such that 
> you had to have at least as much swap as RAM but that's no longer 
> true. Now, you don't have to have any swap at all. The amount of swap 
> you need is a relatively simple calculation:
>
> swap needed = virtual address space needed - physical memory available
>
> The tricky part of this sadly is determining the correct value of 
> "virtual address space needed" :-)
>
>
>
> Niall
>
I'd agree with that, the sad bit.

Make it big (swap = 2 x RAM ) and then monitor...

Then make it smaller. And if going to less swap than RAM make sure not 
older OS/Kernel that borks at such an idea.

Not needing disk swap at all of course is the best performance.  I 
thought only Vista needed more than 1.5G :-)

Thinks like databases or webserver applications can seem to take lots, 
but may not really need it if you put the wrong numbers in and if  
"given" to much the rest of the system is doing paging that in reality 
is not needed, more than negating the "big number" put in to "improve" 
the whatever  server  application.  But how  do  you  know  how much  
memory  for  cache  or  whatever is needed on the XYZ application? Much  
harder than identifying total system Virtual Memory usage




Michael Watterson
Senior Development Engineer

T: +353 85 7403830  F: +353 1 2569229  E: mwatterson at digiweb.ie 
A: College Business & Technology Park, Blanchardstown, Dublin 15, Ireland W: http://www.digiweb.ie/