2GB swap partition limit?

[Russell Coker]

On Friday 17 March 2006 00:35, "Mauro Mozzarelli" <mmkernel at ezplanet.net> 
wrote:
> >> > Incidentally such a large swap space will not do you any good in most
> >> > usage scenarios.
> >>
> >> Three words: "suspend to disk".
>
> I use it for "tmpfs"

There are situations where machines can perform very well with a tmpfs that is 
significantly larger than RAM.  There was one time that one of my machines 
with 512M of RAM needed a 6G tmpfs and gave really good performance with 6G 
of swap.

There are also some applications that have a working set which is far smaller 
than the full allocated memory space and which perform well when they are 
mostly swapped out.

However I believe that neither is a common use of a machine.  The general 
advice which is given as "use twice RAM" is something that I believe to be 
wrong in most instances now that machines with 512M of RAM or more are 
common.

The issue of what size of swap space will be viable is really determined by 
the IO capacity of the storage device.  Get a bunch of 15,000rpm SATA or SCSI 
disks in a RAID-5 array with a write-back disk controller and a swap space of 
several gigs in size may be viable for a wide range of work loads.  Get a 
single IDE disk with a few gigs of swap and it's most likely that the 
performance of your machine will be unusable (to a degree that you have to 
press reset as logging in to run shutdown takes far too long) long before the 
swap space is fully used.

I'm not trying to convince people that everyone should use less than 2*RAM for 
their swap space!  Merely that the 2*RAM advice originated when 16M of RAM 
was a big machine and that things are different now.

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