How manu swap ?

[Jerry McAllister]

On Wed, Jan 16, 2008 at 10:28:06AM -0600, Dan Nelson wrote:

> In the last episode (Jan 16), Albert Shih said:
> > Hi all
> > 
> > I known it's classic question. 
> > 
> > Long time ago when I install a FreeBSD x86 32 bits when I have N Go
> > of Ram the installer take 2xN Go for the swap partition.
> > 
> > Now I just install two machine with FreeBSD amd64 version with 8Go of
> > Ram and FreeBSD installer take 4 Go of swap.
> > 
> > Is a bug in the installer or now FreeBSD don't need 2xRam of swap ?
> 
> When was the last time you saw your swap partition with more than 2GB
> in use?  On an 8GB system, you probably will either never have enough
> processes to require swapping at all, or you will have one or two
> processes so big that if they ever swap, it's a sign you need more RAM,
> not more swap :)  In systems with that much RAM, swap is pretty much
> only used for crashdumps, and with minidumps enabled by default, you
> don't need much.  On small systems, the 2x-swap rule was because once
> you allocated enough processes to require that much swap, you were
> pretty much thrashing your system anyway.

Don't forget that the system uses swap space to do paging too and
that frequently used processes can end up in swap and be run from
there faster than from regular disk.

But, yes, the 2X rule was generally a combination of space for
crash-dump plus room to run more than memory can hold.

////jerry


> 
> -- 
> 	Dan Nelson
> 	dnelson at allantgroup.com
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