adding more ram
Robert Watson
rwatson at freebsd.org
Wed Dec 10 21:01:41 PST 2003
On Wed, 10 Dec 2003, Dan Nelson wrote:
> In the last episode (Dec 10), nbari at unixmexico.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.watson.org Senior Research Scientist, McAfee Research
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