adding more ram

[rwatson at freebsd.org (Robert Watson)]

On Wed, 10 Dec 2003, Dan Nelson wrote:

> In the last episode (Dec 10), nbari_(_at_)_unixmexico_(_dot_)_com said:
> > I have a server with 1GB of RAM and a swap partition of 2GB i will
> > upgrade the memory server to 2GB so my questions are:
> > 
> > should i fix the swap partition to have now 4GB of space ?
> 
> Depends.  Have you ever used up that 2gb of swap?  If not, you'll
> probably never consume 4gb either :)  If this is a database server, or
> something similar where a few processes allocate large amounts of
> memory, you don't need much swap anyway, since if any of those processes
> actually has to swap, you end up thrashing the system as it tries to
> swap 500mb processes in and out of memory.  I really can't think of a
> system that would still perform well with 2 or 3GB of process space in
> swap.  At the 2gb RAM point, you usually have a system where any
> swapping == bad news. 

Actually, the thing I use swap for most now is to make sure I can allocate
large temporary file systems without consuming excessive kernel address
space.  I.e., I'll often create a 512mb swap-backed md device for /tmp,
and make sure I have enough swap to fully back it and everything else,
even though the chances are I won't touch it in normal operation.  I just
don't want to run out in the event something does need it...

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert_(_at_)_fledge_(_dot_)_watson_(_dot_)_org      Senior Research Scientist, McAfee Research