2GB swap partition limit?
Horst von Brand
vonbrand at inf.utfsm.cl
Thu Mar 16 21:24:51 UTC 2006
Lamont R. Peterson <lamont at gurulabs.com> wrote:
> On Thursday 16 March 2006 10:14am, Horst von Brand wrote:
> > Russell Coker <russell at coker.com.au> wrote:
> > > 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.
> > Exactly. Plus disk (even expensive, high-end ones) are /s l o w/. You need
> > to put enough RAM into the machine for what it needs, in which case you use
> > swap mostly for whatever load spikes run over that, and you care enough not
> > to let OOM take over... and that is completely unpredictable, unless you
> > have a very detailed knowledge of the expected load, so any "swap is X
> > times RAM" advise is bogus. But then again, disk is cheap, and you have to
> > tell people /something/...
> IMHO, the main reason that the common advice is something like "2x RAM" is
> that those in the know were not willing or able (for whatever reason(s)) to
> explain the real truth to newbies,
Try my above rant on the average newbie, and see eyes glazing over and feel
(more than see) the irresistible urge to run away from all such complexity,
> and that led to people thinking that it
> was some magic number.
> I've even heard otherwise intelligent, knowledgeable
> admins tell people that you *absolutely must* make swap 2x RAM or it won't
> work or "performance will be horrid at best."
Some Solaris boxen had to have swap > RAM, or it wouldn't be of any use, so
2x RAM was a reasonable compromise.
> But, it's understandable; not everyone can take the time required to
> properly educate.
Some of us try, but it is hard.
Dr. Horst H. von Brand User #22616 counter.li.org
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