[CentOS] Re: Apparently no swap configured

Karanbir Singh mail-lists at karan.org
Thu Oct 30 10:28:38 UTC 2008


Stephen Harris wrote:
>> " 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.

I disagree with that. It has been true for linux for a long time, and is 
true even now. When was the last time you looked at the linux swap 
handling code ?

Recently, with large amounts of ram available on physical machines, eg > 
2 GB, you need to start reconsidering a part of that strategy based 
around the fact that if your machine is really using 2 GB+ of swap, 
there might be other problems that need fixing and the absurd levels of 
latency introduced by that would mean those other issues really need 
looking at.

I'd still go with 2xRAM size for swap size upto a swap size of 2 GB, 
then make it the same as RAM size, till you get to 32 GB, at which 
point, half of real RAM size till 128 GB. Beyond that point, you really 
should be doing some benchmarks and monitoring to work out how much swap 
you need, and where it needs to be.

The other school of thought that seems to be doing the rounds is, 2xRAM 
till 4 GB, then just leave swap at 4GB irrespective of what your real 
machine RAM is, as long as its a multiple of 4.

-- 
Karanbir Singh : http://www.karan.org/  : 2522219 at icq


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