Stephen Harris wrote:
On Wed, Oct 29, 2008 at 09:56:34AM -0400, James B. Byrne wrote:
I believe that the current recommendation is 2 x physical memory up to 2
GB and then 1 x physical memory thereafter.
See:
http://www.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5.2/html/Deployment_Guide/s1-swap-what-is.html
" Swap should equal 2x physical RAM for up to 2 GB of physical RAM, and
then an additional 1x physical RAM for any amount above 2 GB, but never
less than 32 MB.
That's a silly recommendation, and never been true for Linux. RedHat
don't always know what they're talking about.
In older BSD systems (eg around SunOS 4 times or before) swap space was
utilised oddly; all memory was allocated from swap, so you needed _at
least_ <physmem> of swap just to use all your real memory! So if you
added <physmem> of swap then your total virtual memory size was still
only <physmem>. No help! So the rule of thumb came along that said
"swap = 2*<physmem>" and that gave you a VM of 2*<physmem>. Linux never
did this (and I don't think modern BSDs do, either) so adding <physmem>
of swap will automatically give you twice <physmem> of VM.
Ah, yes, not an older release of Solaris...SunOS4
A certain release of SunOS4 required swap be twice the amount of RAM or
it would crash according to an article that I read but I cannot find
right now. Here is a FAQ article related to SunOS that tells us how
SunOS4 handled virtual memory (swap must be at least the same amount of
RAM): http://www.bjnet.edu.cn/sun-admin/FAQ/F-comp-sys-sun/Q30-0.html
The source of this 'recommendation' that swap be twice that of RAM is
affects more than just Linux
http://blogs.sun.com/jimlaurent/entry/solaris_faq_myths_and_facts
So please, stop spreading this swap should be twice the amount of RAM
installed nonsense.
/me gets off soapbox.
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