On Thursday 16 March 2006 10:14am, Horst von Brand wrote: > Russell Coker <russell@xxxxxxxxxxxx> wrote: > > On Friday 17 March 2006 00:35, "Mauro Mozzarelli" <mmkernel@xxxxxxxxxxxx> > > > > 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. > > 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, 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." But, it's understandable; not everyone can take the time required to properly educate. -- Lamont R. Peterson <lamont@xxxxxxxxxxxx> Senior Instructor Guru Labs, L.C. [ http://www.GuruLabs.com/ ] GPG Key fingerprint: F98C E31A 5C4C 834A BCAB 8CB3 F980 6C97 DC0D D409
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